little otter creek watershed: phase 2 stream geomorphic assessment

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    Little Otter Creek Watershed:Phase 2 Stream Geomorphic Assessment

    Addison County, Vermont

    July 2011

    Little Otter Creek including South Slang and East Slang above confluence with Lake Champlain,view to the northwest, 25 March 2010

    Prepared under contract to Prepared byLewis Creek Association442 Lewis Creek RoadCharlotte, VT 05445

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    TABLE OF CONTENTS

    ACKNOWLEDGEMENTS.............................................................................................................................................. iiEXECUTIVE SUMMARY.............................................................................................................................................. iii

    1.0 INTRODUCTION .............................................................................................................................................. 12.0 BACKGROUND.................................................................................................................................................. 2

    2.1 Geographic Setting ...................................................................................................................................... 22.2 Regional Geologic Setting .......................................................................................................................... 4

    2.2.1 Bedrock Geology.................................................................................................................................. 52.2.2 Surficial Geology .................................................................................................................................. 6

    2.3 Geomorphic Setting..................................................................................................................................... 72.4 Hydrology ................................................................................................................................................... 102.5 Flood History .............................................................................................................................................. 122.6 Ecological Setting ...................................................................................................................................... 142.7 Land Use ..................................................................................................................................................... 152.8 Water Quality ............................................................................................................................................. 17

    3.0 ASSESSMENT METHODOLOGY.................................................................................................................... 213.1 Phase 2 Stream Geomorphic Assessment .............................................................................................. 213.2 Phase 1 Assessment Updates .................................................................................................................. 223.3 Quality Assurance / Quality Control ........................................................................................................ 23

    4.0 PHASE 2 ASSESSMENT RESULTS ................................................................................................................ 244.1 Little Otter Creek main stem - New Haven, Monkton, Bristol............................................................ 244.2 Mud Creek tributary - Ferrisburgh ......................................................................................................... 32

    5.0 DEPARTURE ANALYSIS, STRESSOR IDENTIFICATION & SENSITIVITY............................................... 355.1 Departure Analysis .................................................................................................................................... 35

    5.1.1 Watershed Scale Hydrologic and Sediment Regime Stressors................................................ 365.1.2 Sediment Regime Stressors (Watershed and Reach Scale) .................................................... 515.1.3 Reach Scale Modifiers ....................................................................................................................... 525.1.4 Constraints to Sediment Transport & Attenuation........................................................................ 54

    5.1.5 Sediment Regime Departure............................................................................................................ 555.2 Sensitivity Analysis .................................................................................................................................... 60

    6.0 PRELIMINARY PROJECT IDENTIFICATION ............................................................................................... 626.1 Protecting River Corridors ........................................................................................................................ 636.2 Planting Stream Buffers ............................................................................................................................ 656.3 Stabilizing Stream Banks .......................................................................................................................... 666.4 Arresting Head Cuts and Nick Points ...................................................................................................... 666.5 Removing Berms / Other Constraints to Flood & Sediment Load Attenuation ................................. 666.6 Removing / Replacing Structures ............................................................................................................ 67

    6.6.1 Bridge and Culvert Crossings ........................................................................................................... 676.6.2 Old Abutments ................................................................................................................................... 69

    6.7 Restoring Incised Reaches ....................................................................................................................... 696.8 Restoring Aggraded Reaches ................................................................................................................... 706.9 Mitigating Sources of Stormwater and Nutrient / Sediment Loading ................................................ 706.10 Restoring Riparian Wetland Hydrology .............................................................................................. 72

    7.0 ADDITIONAL MANAGEMENT STRATEGIES................................................................................................ 737.1 Continued Strategic Planning by Watershed Stakeholders.................................................................. 737.2 Coordinated Support to Farmers ............................................................................................................. 737.3 Enhanced Protections for Vulnerable Geologic / Hydrologic Settings ................................................ 737.4 Workshops.................................................................................................................................................. 747.5 Outreach to Towns .................................................................................................................................... 74

    8.0 REFERENCES.................................................................................................................................................. 76

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    APPENDICES

    A. Updated Phase 1 Stream Geomorphic Assessment Reach Summary ReportsB. Phase 2 Stream Geomorphic Assessment Segment Summary ReportsC. Bridge & Culvert Assessment Summary ReportsD. Valley Wall DocumentationE. Quality Assurance DocumentationF. Reach SegmentationG. Reach NarrativesH. Stressor Table, Reach-ScaleI. Departure Analysis Table, Reach-Scale

    ACKNOWLEDGEMENTS

    This study was made possible through grant funding received from the State of Vermont Department ofEnvironmental Conservation, Division of Water Quality. The grant was administered by the Lewis CreekAssociation on behalf of the Addison County River Watch Collaborative. Technical assistance wasprovided by the VT Department of Environmental Conservation, River Management Program. HapEliason, pilot, provided flight services for aerial assessment of the watershed in the Spring of 2010. JohnMcNerney, pilot, provided flight services for the Spring 2011 flyover. The project was guided by aSteering Committee of watershed stakeholders:

    Project Steering Committee

    Marty Illick Lewis Creek Association, Addison County River Watch CollaborativeEthan Swift VTDEC Mapping, Assessment & Planning Program

    Shannon Pytlik VTDEC River Management Program

    Brian Jerose WASTE NOT Resource Solutions

    Kevin Behm Addison County Regional Planning Commission

    Craig Miner USDA Farm Service Agency (Middlebury)

    Keith Hartline USDA Natural Resources Conservation Service (Middlebury)

    John Thurgood USDA NRCS District Conservationist

    Jeff Carter UVM Agricultural Extension Service (Middlebury)

    Rico Balzano UVM Agricultural Extension Service (Middlebury)

    Pam Stefanek Addison County Natural Resources Conservation District

    April Moulaert Waterscapes, LLC (representing Ducks Unlimited)

    Allen Karnatz Vermont Land Trust

    Kristen Underwood South Mountain Research & Consulting

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    EXECUTIVE SUMMARY

    A stream geomorphic assessment and preliminary river corridor planning effort were completed in 2010-2011 for the Little Otter Creek watershed focusing on 11 reaches (12.7 river miles) of the Little OtterCreek main stem and Mud Creek tributary. This study was made possible through grant funding receivedfrom the State of Vermont Department of Environmental Conservation (VTDEC), Water Quality Division(WQD). The grant was administered by the Lewis Creek Association on behalf of the Addison CountyRiver Watch Collaborative (ACRWC). This project involved a variety of data collection approachesincluding: Phase 2 stream geomorphic assessments; remote-sensing and windshield surveys; evaluationof existing flow data; and evaluation of existing water quality monitoring data. Additionally, guidancewas offered by a Steering Committee convened for this specific project, comprised of representativesfrom the VTDEC WQD Monitoring, Assessment & Planning Program and River Management Program;

    USDA Natural Resources Conservation Section; Addison County Natural Resources Conservation District,UVM Agricultural Extension Service, Ducks Unlimited (represented by Waterscapes, LLC); Vermont Land

    Trust and WASTE NOT Resource Solutions. Project data were compiled and evaluated to inform thecommittee and to identify and prioritize restoration and conservation projects for implementation.

    Assessments in the Little Otter Creek watershed were undertaken to identify projects which will reducenutrient and sediment loading from the watershed and to provide a geologic, geomorphic andhydrologic context for documented erosion and water quality issues. Long term water quality monitoringby the VTDEC and ACRWC has identified elevated levels of phosphorus and turbidity. Nine miles of theLittle Otter Creek channel have been listed as impaired for aquatic life support and contact recreation

    uses due to E.coliand other undefined pollutants resulting from agricultural runoff (2010 303d List ofImpaired Waters). Four miles of the Mud Creek tributary are also identified for further assessment due toE. coliimpacts to contact recreation uses associated with agricultural runoff (2010 Part C List of PrioritySurface Waters in need of Further Assessment). These documents identify the Little Otter Creek as aHigh priority for development of a Total Maximum Daily Load (TMDL) plan to address water quality

    impacts.

    The susceptibility of Little Otter Creek to water quality impacts is directly related to the underlyinggeology, topography and hydrology of this watershed. Watershed sediments are dominantly comprisedof silt and silty-clays derived from a fresh-water lake and the Champlain Sea which inundated the areafrom approximately 13,500 to 10,000 years ago. Soils have low to very low infiltration rates and arehydric in nature. Stream-connected wetlands are wide-spread (where they have not been previouslyconverted to agricultural use by drain tile and field ditches). Along the river network, there areoccasional valley pinch points where the channel crosses regional fault features in the underlying bedrock- such as, a short segment between Lime Kiln Road and Monkton Road at the Monkton / Ferrisburghtown line; the bedrock gorge (Walkers Falls) off Wing Road in Ferrisburgh, or Birketts Falls at theSatterly Road crossing in Ferrisburgh.

    Given the low valley gradients and prevalence of hydric soils and contiguous wetlands, the channel and

    floodplain above these valley pinch points are frequently inundated following storm events. These areasare inundated during flows that occur on an annual and more frequent basis. Flood waters are stored for

    several days above the valley pinch points, and are slowly released to downstream reaches. Thus, floodpeaks recorded at a US Geological Survey stream flow gage on Route 7 gage have a very broad and low-magnitude crest.

    Given the topography and geology of the Little Otter Creek watershed, the river is well connected to itsfloodplain and attenuates flows much more effectively than neighboring more flashy rivers prone of flood-

    related erosion hazards. However, the fine soils and broad valleys make these areas prone todevelopment and agricultural uses, where sources of nutrients and sediment can intersect surface

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    waters. Land use in the watershed overall is 51% agricultural, and 3% developed, with only 25% inforest cover. The silt and clay particles dominating floodplain soils have a high affinity for phosphorus.The Little Otter Creek is a washload-dominated river, where fine sediments (and associated nutrients)tend to stay in suspension and travel for great lengths downstream (ultimately to Lake Champlain).

    This study focused on 10 reaches of the Little Otter Creek main stem from Plank Road in New Haven

    downstream nearly to the Satterly Road crossing in Ferrisburgh and one reach of the Mud Creek from theMiddlebrook Road crossing downstream to the confluence with Little Otter Creek. Geomorphicassessments, windshield and aerial surveys, and limited historical reviews have identified variouswatershed and channel stressors that have impacted the assessed reaches, including:

    Watershed-scale Stressors:

    Historic conversion of wetlands for agricultural and residential land uses through ditching oftributaries, and installation of field-ditch and tile-drain networks; these drainage networkshave increased the magnitude and velocity of flows to the Little Otter Creek and areassociated with increased frequency and duration of inundation of the floodplain in activelyfarmed areas.

    Installation of 138 miles of roads which intersect the Little Otter Creek stream network inmore than 270 locations; road ditches associated with this transportation network haveincreased the stream network density and provide for direct runoff of stormwater, nutrientsand sediments from unbuffered farm fields and developed lands to the Little Otter Creek.

    Historic deforestation and subsequent reforestation of the watershed from the mid-1800sthrough the early 1900s;

    Significant flood events in 1931, 1927, 1936, 1938, 1973 and 1976; more recently, a 10- to25-year event occurred in January of 1996, and an August 2004 flood event impacted theheadwaters; and

    Documented increases in annual precipitation and the frequency and number of intenseprecipitation events over the last century in the Northeastern United States (UNH ClimateChange Research Center, 2005).

    Reach-scale Stressors:

    Historic channelization, berming, and armoring (rip-rap) limited to road crossing sites; Stormwater runoff from agricultural fields via ditches and tile-drains; Stormwater runoff from roads/driveways and road ditches; Undersized public and private bridges and in-stream culverts, serving as flow constrictors at

    bankfull flow or higher-magnitude flood events;

    With a couple of exceptions, the main channels of the Little Otter Creek and Mud Creek (at least in theassessed reaches) are stable. This river is not exhibiting the kinds of extreme lateral and vertical channel

    adjustments that characterize higher-relief, gravel-bed streams impacted by similar types of stressors

    (such as the nearby New Haven River). Channel segments of the Little Otter Creek are well connected tothe surrounding floodplain and operate effectively to attenuate flows. The overall channel isdemonstrating an expected (natural) level of change or adjustment in response to stressors, maintainingaverage dimensions, planform, and profile, over time. At present, enhanced erosive energies that mayhave resulted from watershed and channel stressors, appear to be balanced by the resisting forces of thechannel margins (e.g., forested buffers, cohesive sediments; bedrock exposures in some reaches), andare moderated by low gradients, bedrock grade controls, and channel-connected wetlands.

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    Three relatively short sections of the assessed main stem have become partially disconnected from theirsurrounding floodplain, following historic channel manipulations associated with road crossings. Modifiedsegments are located near the North Street and Plank Road culvert crossings of the upper main stem inNew Haven; and at the Monkton Road bridge crossing in Ferrisburgh.

    While assessed main-stem reaches of the Little Otter and Mud Creek are generally stable, the stream

    network contributing to these reaches has been extensively modified. First, second and third-ordertributaries have been straightened and channelized, and periodically dredged and bermed in support ofagricultural operations and to accommodate roads and residential / commercial uses. To improvedrainage on wet soils, fields have historically been ditched and drainage tiles have been installed. Thesedrainage networks and channelized tributaries have increased the magnitude and velocity of flows to theLittle Otter Creek. Over the last two centuries, 138 miles of roads have been installed on the landscape

    and intersect the Little Otter Creek stream network in more than 270 locations. Road ditches associatedwith this transportation network have effectively increased the stream network density and provide for

    direct runoff of stormwater, nutrients and sediments from unbuffered farm fields and developed lands tothe Little Otter Creek.

    Because of the high clay content of Addison County soils, fields are typically plowed in the fall and remainexposed during the most vulnerable runoff conditions. Based on review of the 20-year hydrologic record

    for the Route 7 USGS gage, 80% of the high flows occur in the late Fall, Winter or early Spring whenfields are bare.

    Anecdotally, the frequency and duration of inundation within the low-lying floodplains upstream of valley

    pinch points has increased in recent decades (e.g., upstream of Lime Kiln Road in Monkton, spanning thePlank Road crossing of a tributary to the Little Otter in New Haven, and upstream of Satterly Road anddownstream of Middlebrook Road in Ferrisburgh). This may be due in part to climate changes which

    have resulted in documented increases in annual precipitation and the frequency and number of intenseprecipitation events over the last century (UNH Climate Change Research Center, 2005). Modifications to

    the Little Otter Creek stream network and impacts from field-ditch, tile-drain, and road-ditch networkshave undoubtedly also contributed.

    While several areas of the Little Otter Creek/ Mud Creek floodplain are well connected to the channel and

    are frequently inundated, the natural wetland functions and values of these inundated areas have beencompromised by conversion to agricultural uses and impacts from field-ditch and road-ditch networks.Flood retention and filtering functions of these wetlands have been significantly reduced through historic

    clear-cutting of native floodplain tree species, compaction and leveling of soils through repeated tillage(loss of micro-topography), and dredging of linear ditch networks to improve field drainage. Sedimentand nutrients are impacting these prior-converted wetland areas (both within and along the edges of

    frequently inundated areas).

    Significant mobilization of fine sediments, phosphorus and nitrogen is occurring within the Little OtterCreek watershed, related to: (1) a legacy of nutrient additions in excess of agronomic needs; (2) fall-tilling, manure applications, and cropping practices in close proximity to unbuffered swales, road ditches

    and other locations of concentrated runoff to surface waters; (3) frequent inundation of fields wellbeyond minimum buffer widths required by Accepted Agricultural Practices and Large Farm Operation /

    Medium Farm Operation rules; (4) maintenance of tile networks and drainage ditches in agriculturalfields; and (5) stormwater and sediment runoff from road networks.

    Opportunities for river restoration and conservation and improved farm and road management have beenidentified based on results of this stream geomorphic assessment and a limited river corridor planning

    effort. A preliminary project listing forms the basis for follow-on project development and planningactivities which can be carried out by watershed stakeholders. A subset of the identified projects has

    progressed through development phases.

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    1.0 INTRODUCTION

    This report presents the results of Phase 2 stream geomorphic assessments and preliminary river corridor

    planning efforts completed in 2010. Assessment focused on eleven reaches (12.7 river miles) of the LittleOtter Creek and Mud Creek located in the towns of New Haven, Monkton, and Ferrisburgh. Geomorphicassessments were completed to:

    a) determine the geomorphic condition of targeted reaches, and identify active vertical and lateraladjustment processes;

    b) identify current and historic channel and watershed disturbances that may lead to vertical andlateral adjustments; and

    c) evaluate the sensitivity of reaches to future channel and watershed stressors given their currentgeomorphic condition and inherent vulnerability (e.g., valley setting, slope, streambed and

    streambank sediments, vegetative buffer conditions).

    In addition, windshield and aerial surveys were conducted during high water conditions, and remote-sensing data were reviewed to:

    d) identify locations of direct stormwater and agricultural runoff to the Little Otter Creek network;and

    e) identify areas of saturation excess overland flow that overlap nutrient and sediment source areas(Critical Source Areas);

    Based on assessment data, and guided by a Steering Committee of watershed stakeholders, projects andstrategies have been identified for implementation at the site-level, reach-level and community scale.The current status of project development is summarized on the Project CD. Overall objectives of this

    ongoing planning process are to:

    mitigate for the effects of hydrologic and sediment regime modifications; decrease nutrient and sediment loading; and improve water quality, restore habitats, and reduce erosion hazards by managing toward the

    equilibrium channel.

    This summary report has been prepared by South Mountain Research & Consulting (SMRC) based inBristol, Vermont for the Addison County River Watch Collaborative, under contract to its fiscal agent, theLewis Creek Association. This project has been funded in part by a grant from the VT Department of

    Environmental Conservation. Project tasks have been carried out by the Lewis Creek Association (LCA)and South Mountain Research & Consulting (SMRC) of Bristol, VT, with technical support from the VTDEC

    Mapping, Assessment & Planning Program and the River Management Program. Members of the projectSteering Committee are identified in the Acknowledgements section (page ii).

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    2.0 BACKGROUND

    Assessments in the Little Otter Creek watershed were undertaken to provide a geologic, geomorphic and

    hydrologic context for the erosion and water quality issues documented in this river network over thepast several years.

    2.1 Geographic Setting

    The Little Otter Creek watershed is a 72.5-square-mile basin located in Addison County, Vermont,draining portions of six towns (Table 1, Figure 1):

    Table 1. Area of Addison County towns contained

    within Little Otter Creek watershed.

    Town Area (sq mi) Area (% watershed)

    Ferrisburgh 28.0 38.6%

    New Haven 21.4 29.5%

    Monkton 13.5 18.6%

    Bristol 6.5 8.9%

    Waltham 3.0 4.2%

    Vergennes 0.1 0.2%

    To tal: 72.5

    Figure 1. Location of

    Little Otter Creek watershedwithin Addison County towns.

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    2.2 Regional Geologic Setting

    The Little Otter Creek watershed is contained wholly within the Champlain Valley geologic province(Stewart, 1973; Capen, 1998). The Champlain Valley is underlain primarily by limestones and dolostones

    which have undergone low-angle thrusting and folding, to create locally elevated slabs of crystalline caprock. Champlain Valley rocks are less-intensely deformed than the phyllites, schist, and gneiss of theneighboring Northern Green Mountain province to the east, yet create local relief (Stewart, 1973). Thenortheast-trending Monkton Ridge extends into the northern central portion of the watershed (see Figure

    2), creating relief in the area of The Watershed Center (former Vergennes water supply). In the westernportion of the watershed, a major thrust fault zone called the Champlain Thrust has resulted in the

    erosional remnants of Shellhouse Mountain and Buck Mountain.

    In recent geologic time (from 24,000+ to 13,500 years before present; Ridge, 2003) this landscape was

    occupied by advancing and retreating glaciers, with ice up to a mile or more in thickness above thepresent land surface. Glacial tills now blanket much of the upper bedrock-controlled slopes in the

    headwaters of the eastern and northeastern part of the Little Otter Creek watershed. As glaciers meltedand receded, deposits of water-washed boulders, cobbles, gravel and sand (kame moraines, kame

    terraces) built up along the ice margins near the contact between the Champlain Valley and the NorthernGreen Mountains (Stewart, 1973; Stewart & MacClintock, 1969) along the western sides of Hogback andSouth Mountains to the east of Little Otter Creek.

    As the global climate warmed and the glaciers receded, a large fresh-water lake inundated the HudsonValley Lowland (Lake Albany) and later extended northward into the Champlain Valley (Lake Vermont)(Connally & Sirkin, 1969; Chapman, 1937; Stewart & MacClintock, 1969; DeSimone & LaFleur, 1985).Since flow was blocked to the north by the retreating Laurentide ice lobe, freshwater entering LakeAlbany / Lake Vermont drained to the south via the Hudson River valley to Long Island, NY. At itshighest stage, the Lake Vermont shoreline extended to the foot of the Green Mountains near the presentlocation of Starksboro Village, Bristol village, and East Middlebury. Glacial meltwater flowing west fromthe Green Mountains built large deltas of sands, gravels, cobbles, and boulders which extended out intoLake Vermont. Further to the west, theisolated bedrock knobs and ridges such as Shellhouse Mountain

    and Buck Mountain, were islands emerging above the surface of Lake Vermont.

    Lake Albany / Lake Vermont waters receded in stages as natural dams in southern Vermont and NewYork gave way. The Laurentide ice lobe retreated further to the north and east, until the St. Lawrence

    valley was no longer blocked by ice. From approximately 13,100 to 12,700 years before present (Ridge,2003), marine waters filled the valley from the St. Lawrence Seaway as the rate of rise in ocean waterlevels temporarily exceeded the rate of rise [isostatic rebound], of the land surface now relieved of its

    glacial burden (Stewart and MacClintock, 1969; Cronin, 1977; Wagner, 1972; Connally and Calkin, 1972).The maximum elevation of these brackish waters is believed to have extended into the present-day LittleOtter Creek watershed, perhaps not much farther east than the villages of Ferrisburgh and Vergennes(Wagner, 1972). Champlain Sea waters receded from the greater Champlain Valley, as the rate of landrise began to outpace the rate of sea-level rise. A lower stage of fresh water (analogous to present-day

    Lake Champlain) then filled the Champlain Lowland. Surface waters from the Lake Champlain basin nowdrain to the north, while the Hudson River basin continues to drain to the south.

    The landscape of Vermont was dissected by river systems following glacial retreat, driven in part bydropping base levels in the Hudson River valley and Lake Champlain. Significant channel incision mayalso have been driven by isostatic rebound of the land surface in the late Pleistocene and early Holocene(Brakenridge et al, 1988). The Little Otter Creek river network eroded downward through glacial-fluvialkame terrace deposits (at the southeastern extent of the watershed) and silt- and clay-rich lake deposits.Downward incision was apparently arrested at exposures of channel-spanning bedrock along the rivernetwork, including Walkers Falls off Wing Road in Ferrisburgh and Frasers Falls off Little Chicago Road in

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    Ferrisburgh. Today, these bedrock nick points serve as fixed base levels for upstream reaches of theLittle Otter Creek and its tributaries.

    Absence of vegetation on the recently-deglaciated hillslopes probably contributed to floodplainaggradation in the late Pleistocene. Sedimentation rates would have declined as the landscape becamerevegetated and forests matured; floodplain incision may have begun to dominate again. Rates ofsedimentation on alluvial fan surfaces and in ponds were relatively high during the early Holocene based

    on research from Northwestern Vermont (Bierman et al, 1997). Bierman et al (1997) theorize thatearly Holocene hillslope erosion may have been driven by episodic large storms in a drier [but stormier]climate than today. Late Holocene erosion and aggradation were also event driven, but greater ambient

    levels of soil saturation [in a cooler, moister climate] may have allowed smaller storms to trigger similarlandscape responses. In colonial times, hillslope erosion and floodplain aggradation increasedsubstantially as a result of wide-spread deforestation by the early- to mid-1800s (Brakenridge et al, 1988;Severson, 1991; Thomas, 1985). These trends may have again reversed themselves when mosthillslopes became reforested in the late 1880s and early 1900s.

    2.2.1 Bedrock Geology

    In general, bedrock geology of the Little Otter Creek watershed can be grouped into two main categories:

    Cambrian and Ordovician limestones, dolostones and marbles of the Champlain Valley lowland(Stewart, 1973; Doll, 1961); and

    Cambrian quartzites forming the ridges within the Champlain Valley province (Stewart, 1973;Doll, 1961).

    The Little Otter Creek river network is influenced by the underlying bedrock geology in many ways. Thequartzite cap rocks forming the mid-watershed ridgelines of Monkton Ridge, Shellhouse Mountain, andBuck Mountain are relatively resistant to chemical and physical weathering, while the limestones andother calcitic rocks of the surrounding Champlain Lowland are less resistant to erosion. In this way, the

    bedrock geology of the basin controls the regional topography.

    Regional, structural features of the bedrock control local topographic and govern drainage patterns. TheLittle Otter Creek headwaters at the far eastern extent of the watershed drain steep slopes onglaciofluvial deposits at the base of Hogback Mountain and South Mountain which are formed by theHogback Anticline (Stewart, 1973). The channel then meanders through a very large wetland complex

    known as the Cedar Swamp, before crossing the southern end of Monkton Ridge in northern New Haven(Figure 2). The Monkton Ridge is formed by quartzite cap rocks exposed in a northeast-trending band bythe Monkton Thrust. The Little Otter Creek then flows through a broad, low-gradient dolomite valley

    between Monkton Ridge to the east and the Vergennes Thrust which forms Shellhouse Mountain andBuck Mountain to the west. The Mud Creek tributary drains a narrow dolomite valley between these two

    mid-watershed quartzite ridge-lines, flowing north from Waltham to join the main stem in southeasternFerrisburgh. These channels cut to the north and west across the regional thrust faults and northeast-

    trending bands of moderately-resistant quartzite to drain ultimately to Lake Champlain.

    Bedrock exposures influence the Little Otter Creek valley confinement, channel position, and profile at a

    reach scale. Locations of channel-spanning bedrock offer vertical grade control, preventing possibledownward erosion of the channel in response to regional or local stressors (at least for the 10- to 100-year time spans of this study). Occasional bedrock exposures along the valley walls control the lateralposition of the channel. Where the river has cut across regional bedrock structures at points ofweakness, bedrock-controlled steep valley walls form valley pinch points along the planform of the river.

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    2.2.2 Surficial Geology

    The nature of the surficial sediments and soils present in the Little Otter Creek watershed reflects theglacial and post-glacial lake history of the region. Upland slopes are dominated by shallow- to moderate-thickness glacial till deposits overlying bedrock. These till deposits are typically a dense mixture of

    sediment sizes from silts to cobbles and boulders; the till sediments are typically cohesive and of lowpermeability (Stewart, 1973; Stewart & MacClintock, 1969; Calkin, 1965).

    At the foot of the Hogback Mountain and South Mountain in the far southeastern extent of the watershed

    (vicinity of Bristol village) are kame terrace deposits of sands, gravels and cobbles which formerlydeveloped at the marginal contact between the glaciers and the mountains. These kame terrace depositsare interlayered with delta deposits from the post-glacial New Haven River (Mack, 1995).

    Out in the broader Champlain Valley, in the central and western portions of the watershed, the landscape

    is dominated by clay and silt deposits generated during former occupation by Lake Vermont (andChamplain Sea, west of Ferrisburgh and Vergennes). These locations would have been in deeper

    sections of the lake, far from the eastern shorelines which were actively receiving runoff from the GreenMountains. Layer upon layer of fine-grained silts and clays were deposited in the quiet lake waters inalternating sequences resulting from annual cycles of spring and summer storm activity followed by

    winter quiet. Exposures of these varved clays, or rhythmites, were noted in the Little Otter Creek andMud Creek channels east and west of Middlebrook Road. The clay and silt deposits of the ChamplainValley contain frequent large boulders. It is hypothesized that these boulders were contained within or

    on rafts ofice which broke off in large blocks from the edge of the receding ice sheet and floated outinto Lake Vermont. As the ice blocks melted, their cargo was released, dropping out to settle in the clay

    and silt deposits at the bottom of the lake. The higher elevations such as Monkton Ridge, ShellhouseMountain and Buck Mountain which remained isolated above lake-level, today are veneered withrelatively thin to negligible deposits of glacial till (Stewart & MacClintock, 1969; Calkin, 1965).

    Soil survey mapping for the watershed (USDA, 2006: USDA, 2007) indicates soil type distributions

    consistent with mapped surficial geology. Figure 3 depicts the generalized soil types in the watershed,grouped by geologic parent material. Land areas in the eastern extent of the watershed are dominatedby soils derived from glacial till, as well as a small area of glacio-fluvial sediments in the southeast

    (vicinity of Bristol village). The central and western portions of the watershed are dominated by siltloams. These silt loams have their origin in silty-clay deposits of marine and freshwater lakeenvironments.

    Sediments of the Little Otter Creek watershed are dominated by soils of low to very low infiltration rate.Nearly 85% of the soil types are classified as C and D Hydrologic Soil Group. The remainder of the soilsare of greater permeability (Hydrologic Soil Groups A and B), tend to be associated with localizeddeposits glaciofluvial and alluvial origin, and are concentrated along the eastern side of the watershedand in isolated pockets along the river network.

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    Figure 3. Generalized map ofsoil parent material in theLittle Otter Creek watershed.NRCS parent materialclassification of lacustrine

    does not differentiatebetween lake silts/clays ofglacial versus marine origin.

    2.3 Geomorphic Setting

    Surface waters of the Little Otter Creek watershed were delineated into a total of 23 reaches in a Phase 1Stream Geomorphic Assessment previously completed by the Addison County Regional PlanningCommission (ACRPC, 2006; see Figure 4). Geomorphic reaches were defined based on variation in valleyconfinement, gradient, and sinuosity, as well as tributary influence (see protocols for furtherbackground).

    Each reach was assigned a unique alphanumeric identification. The 16 reaches along the main stem ofthe Little Otter Creekwere prefixed with a capital M. The seven reaches of the Mud Creek tributarywere denoted with a capitalTand a 2 indicating that Mud Creek is the second major tributary to jointhe main stem. Eleven reaches (12.7 miles) were selected for Phase 2 assessment (Figure 4, Table 2).

    LEGEND

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    Figure 4. Reaches Delineatedin the Little Otter Creek

    Watershed. Reaches selectedfor Phase 2 assessment arehighlighted in red.

    Reach Town

    Channel

    Length (mi)

    Drainage

    Area

    (sq mi)

    M13 New Haven 0.8 11.9

    M12 New Haven 0.9 12.3

    M11 New Haven 1.9 25.5

    M10 Monkton 1.3 35.4

    M09 Ferrisburg 0.5 35.8

    M08 Ferrisburg 1.5 39.4

    M07 Ferrisburg 0.8 39.6

    M06 Ferrisburg 0.3 43.2

    M05Ferrisburg 1.8 45.0

    M04 Ferrisburg 1.8 57.4

    T2.01 Ferrisburg 1.1 9.1

    Little Otter Creek main stem

    Mud Creek Tributary

    Table 2. Reaches of the Little Otter Creekand Mud Creek selected for Phase 2

    Stream Geomorphic Assessment.

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    There are several bedrock-controlled nick points along the longitudinal profile of the Little Otter Creek(Figure 5). High bedrock falls are exposed at a few of these locations, including: Walkers Falls off WingRoad in Ferrisburgh (reach M07); Birketts Falls on Satterly Road in Ferrisburgh (M03); and Frasers Fallsoff Little Chicago Road in Ferrisburgh (at the M02/M01 reach break). Historic names for the bedrock fallsare from a History of the Town of Ferrisburgh (Smith, 1886).

    These bedrock-controlled nick points correspond with valley pinch points, where the river channel is moreclosely confined by the valley walls. The valley pinch points are separated by channel lengths that flowthrough very wide, unconfined, low-gradient valley settings. Given the underlying hydric soils of

    glaciolacustrine origin, the unconfined channel segments are often characterized by wetland conditionsjust upstream of the next bedrock-controlled valley pinch point.

    0

    200

    400

    600

    800

    0 5 10 15 20 25

    Distance Upstream from the Mouth (miles)

    Elevationabovemeansealevel

    (feet)

    Little Otter Creek

    Mud Creek

    Birkett's Falls

    Frasers Falls

    Walkers Falls

    Figure 5. Longitudinal profile of Little Otter Creek and Mud Creek Tributary.

    For a majority of the assessed reaches of the Little Otter Creek, streambank sediments are dominated bythe lacustrine boulder clay and silt deposits of former Lake Vermont (and Champlain Sea in the lowerwatershed). Clays and silts are more dense and more cohesive than unconsolidated sand and graveldeposits; therefore, they are generally more resistant to downward erosion by the Little Otter Creek.

    However, these cohesive soils can be susceptible to lateral erosion in the form of meander migrationthrough progressive stream bank collapse, particularly in reaches absent of woody and mixed vegetativebuffers. Streambeds are characterized by silts and fine sands with the occasional coarse sand and fine-grained gravels.

    Where the Little Otter Creek channel crosses regional thrust fault features in the bedrock at valley pinchpoints, beds are dominated by cobbles and gravels, with occasional boulders. The larger clasts aregenerally subangular, suggesting limited fluvial transport. It is likely that these boulders have been

    derived from nearby bedrock sources and have been revealed in the bed of the stream, as finer-grainedsediments have been winnowed out over time.

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    Unconsolidated sediments of glaciofluvial and alluvial origin are found in isolated pockets along the LittleOtter Creek network (for example, in reach M13 upstream of the North Street crossing). These coarser-grained materials in the channel banks are very susceptible to erosion (if unchecked by stabilizingvegetation). Shear by flowing water at the toe of channel banks can create oversteepened slopes which

    then collapse under forces of gravity.

    2.4 Hydrology

    The United States Geological Survey (USGS) maintains records for three streamflow gaging stations onthe Little Otter Creek (see Figure 6). Only one of the three (Station #04282650) is currently active, withreal-time data available on the Internet (http://waterdata.usgs.gov/vt/nwis/). Station #04282650 islocated near the Route 7 crossing (reach M02), and measures flow from an approximate drainage area of

    57.1 square miles (or 78.8% of the watershed). This station has daily flow records dating back to 1990,or approximately 20 years.

    Peak flows in the Little Otter Creek watershed tend to be well moderated, due to the low overallgradients and extensive wetland areas which provide for flood storage and attenuation. In contrast,

    other area watersheds tend to be much more flashy. For example, Figure 6 illustrates instantaneousflows (normalized to drainage area) for the Little Otter Creek, New Haven River, Lewis Creek and LaPlatteRiver in response to a September 30 / October 1 (2010) storm. Based on regional weather station data,

    rainfall was fairly uniform and widespread during this event. Prior to the storm, area rivers had beennear baseflow conditions. The hydrograph for New Haven River is much higher and sharply peaked. Thehydrograph for Little Otter Creek illustrates a broader, curved peak of much lower amplitude,characteristic of lower-gradient channels with more flow attenuation. While New Haven River flowspeaked within 24 hours of the end of this storm and had receeded to near baseflow conditions within 48hours, the Little Otter Creek took a couple of days to peak followed by more than two days to recede to apre-storm discharge.

    Figure 6. Hydrograph ofStorm Flow in Little OtterCreek Compared to OtherRegional Watersheds.Instantaneous Flows (USGSProvisional) Normalized to

    Drainage Area.

    http://waterdata.usgs.gov/vt/nwis/http://waterdata.usgs.gov/vt/nwis/http://waterdata.usgs.gov/vt/nwis/http://waterdata.usgs.gov/vt/nwis/
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    A separate flow study by ACRWC has established temporary flow gaging stations at additional sites in thewatershed. Stream flows in the eastern mountainous portion of the Little Otter Creek watershed(upstream of reach M13) can be somewhat flashy, given the moderately high relief and thepredominance of shallow bedrock and low-permeability glacial till (Figure 3). Snowmelt events in the latewinter and early spring months can contribute to relatively high discharges.

    Periodic ice jams in the Little Otter Creek may locally enhance flood stages and lead to sudden erosion inbreak-out events. Ice jam events have been recorded near the Route 7 crossing at the lower end of the

    Little Otter Creek (CRREL Ice Jam database, 2010). Occasional blow outs of beaver dams or debris jamsat culvert crossings can also increase flood stages locally.

    The lowest reach (3.7 miles) of Little Otter Creek (below Frasers Falls at the Little Chicago Road crossingin Ferrisburgh) is influenced by backwater effects from Lake Champlain. Historically, water levels in Lake

    Champlain have ranged from a low of 92.6 to 101.9 feet (USGS, 2009). A record-breaking high lake levelof 103.27 feet occurred on 6 May 2011 after record high rainfall in the month of April and the third-

    snowiest winter on record (USGS, 2011). The average annual water level is 95.5 feet (LCBP, 2006).Approximately 13.9 square miles of land area (or 19% of the total watershed area) drains directly to thislower 3.7 miles of river / backwater fed by the Goose Creek and South Slang which drain from thesouthwest and the East Slang which drains from the northeast.

    The Phase 2 stream geomorphic assessments in 2010 were carried out during low-flow to base-flowconditions (Table 3). Daily mean flows recorded at the USGS gaging station (#04282650) located at theRoute 7 crossing in Ferrisburgh ranged from 5.4 to 101 cfs on the assessment dates (Figure 7).Provisional data indicate that the peak flow recorded for water year 2010 the year of the Phase 2geomorphic assessment was 1,400 cfs on 26 January 2010. (A water year extends from 1 October ofthe previous year through 30 September). Two reaches for this project were assessed in late October2010, in the early weeks of water year 2011. A fall storm had occurred in the first couple of days of thewater year leading to a maximum flow of 1,000 cfs on 2 October 2010 (daily mean flow of 878 cfs).

    Table 3. Weather / Flow Conditions on Phase 2 Stream Geomorphic Assessment Dates

    USGS Gage

    #04282650

    Daily Mean

    Date Reach Weather Rain previous 7 days? Flow (cfs)

    5/14/2010 M13 overcast, 60s, breezy, occ.sprinkle 0.2 in on 5/13 (NHR); 0.25 on 5/8 (BTV) 41

    6/18/2010 M13 (addtnl xs's) 80s, breezy, mstly clear 0.36 in on 6/17 (BTV) 20

    6/25/2010 M09 70s, breezy, partly cloudy 0.97 in on 6/24 (BTV) 29

    8/12/2010 M12, M11 70s, breezy, partly cloudy >1 in 8/8 to 8/10 (BTV) 40

    8/13/2010 M10 80s, windy, partly cloudy >1 in 8/8 to 8/10 (BTV) 198/19/2010 M07, T2.01 mstly clear, breezy, 80s, humid 0.13 on 8/16 (BTV) 6.9

    9/10/2010 M08 60s, windy, overcast 0.46 in, 9/7; 0.3 in, 9/9 (BTV) 5.4

    9/23/2010 M06, M05 u/s mstly clear, 60s No 7.3

    10/28/2010 M05 d/s, M04 low 60s, windy, mstly cloudy 0.20 in, 10/27; 0.24 in, 10/24 (BTV) 101

    Abbreviations: BTV = weather station at Burlington International Airport, South Burlington, VT

    NHR = precipitation gage at USGS gaging station #04282525 on New Haven River at Brooksville, VT

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    Figure 7. Daily Mean Flow recorded at Little Otter Creek at Ferrisburg, VT (USGS Stn #04282650)during Phase 2 Stream Geomorphic Assessments, Water Year 2010 and part of 2011.

    2.5 Flood History

    Flood events, particularly higher magnitude flows, can serve as a stressor to the river network leading to

    localized or systemic channel adjustments. Available historic data and USGS flow data were reviewed toidentify flood events of significance in the Little Otter Creek watershed. The Addison County region wasaffected by major flood events of 1913, 1927, 1936, and 1938 (USGS, 1990). The 1927 flood was thehighest flood on record in the State of Vermont. Local residents recall flood events in 1973 (June 30/July 1) and 1976 (August) that were documented in the Otter Creek basin (VTDEC WQD, 1999). A flash

    flood occurring on 28 August 2004 impacted the headwaters of Little Otter Creek in Bristol and NewHaven (NCDC, 2011).

    USGS (Olson, 2002) has estimated the approximate magnitude of peak flows for the gaging station atRoute 7 (Table 4, next page). From the available record, it is evident that the Little Otter Creek has notexperienced a substantial flood event in the previous 20 years (see Figure 8, next page). The maximumpeak flow recorded at the Route 7 gage during this period was 2,210 cfs on 20 January 1996; whichcorresponds to an approximate 10-year to 25-year flood magnitude, or Q10 to Q25 (Olson, 2002; see

    Table 4).

    It should be noted that the estimate for a 2-year frequency storm by Olson (2002), based on availablerecords for that specific gage, (1,120 cfs) is lesser in size than the estimated bankfull flow (Q1.5 = 1,340cfs) for a watershed of that size (57.1 square miles at the gage) based on the VTDEC Hydraulic Geometry

    Curves (2006). The VTDEC curves are based on channels of C and B stream type which tend to be ofhigher gradient with less opportunity for flood storage and attenuation than a watershed such as theLittle Otter Creek, which is dominated by channels of E stream type.

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    Table 4. Estimated flood magnitudes for Little Otter Creek watershed

    USGS Stn # 04282650

    USGS DescriptionLittle Otter Creek at

    Ferrisburg, VT

    USGS Period of Record (flow)

    1990 - present (real-

    time station)

    Upstream Dr. Area (sq mi) 57.1

    Geomorphic Reach M02

    Magnitude Data Source Discharge (cfs)

    Q1.5 (VTDEC, 2001) 1,340

    Q2 1,120

    Q5 1,640

    Q10 (Olson, 2002) 1,990Q25 2,440

    Q50 2,790

    Q100 3,130

    Q500 3,950

    0

    500

    1,000

    1,500

    2,000

    2,500

    1990

    1991

    1992

    1993

    1994

    1995

    1996

    1997

    1998

    1999

    2000

    2001

    2002

    2003

    2004

    2005

    2006

    2007

    2008

    2009

    Water Year

    Discharge

    (cfs)

    2,210 cfs

    1/20/1996

    Q2 = 1,120 cfs

    Q5 = 1,640 cfs

    Q10 = 1,990 cfs

    Q25 = 2,440 cfs

    Figure 8. Recorded Peak Flows for Little Otter Creek at Ferrisburg, VT gage, USGS Stn #04282650

    57.1 square miles, reach M02 (compared to estimated flood peaks after Olson, 2002)

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    2.6 Ecological Setting

    The Little Otter Creek watershed is located wholly within the Champlain Valley bio-geophysical province(Stewart, 1973; Capen, 1998). Broadly speaking, the natural community assemblages in the watershed

    consist of Northern Hardwood Forests and Oak-Pine-Northern Hardwood Forests on the uplands(especially in the northeastern third of the watershed) and Forested Wetlands and Open or Shrub

    Wetlands present in the lowlands (Thompson & Sorenson, 2000).

    Fragments of intact and modified clayplain forest communities are found in the watershed. Documentedroosting habitat for the federally-endangered Indiana Bat is located in the highlands north of Plank Roadand east of North Street (Liz Thompson, personal communication). Roosting and likely foraging habitats

    are also documented between Lime Kiln Road and North Street in New Haven and Monkton (NativeGeographic, 2011). The lowest reaches of the Little Otter Creek near the mouth are characterized as a

    freshwater marsh ecosystem. Approximately 1,000 acres of marsh and upland hardwood forest aremanaged by the VT Fish & Wildlife Department at the Little Otter Creek Wildlife Management Area. Thisarea contains several threatened and endangered bird species, including Osprey, Least Bittern and

    American Bittern.

    The Little Otter Creek is identified as a cold-water stream in the Vermont Water Quality Standards(Vermont Natural Resources Board, 2008). The Biomonitoring & Aquatic Studies Section (BASS) of the

    VTDEC Water Quality Division maintains several fish and macroinvertebrate monitoring stations on theLittle Otter Creek and Mud Creek. Table 5 identifies six BASS stations that are located on the reachesassessed as part of this geomorphic study. Each BASS monitoring station happens to be nearly co-

    located with an existing water quality station maintained by the Addison County River WatchCollaborative (see Section 2.8). These stations are provisionally identified as Warm-Water-Medium-Gradient wadeable stream ecotype ecotypes (Fiske, 2011, personal communication) following theProposed Nutrient Criteria for Vermonts Lakes and Wadeable Streams(VTDEC, 2009).

    Table 5. Location of Biomonitoring Stations on Assessed Reaches of the Little Otter Creek/ Mud Creek.

    Stream Reach

    Nearest Road

    Crossing Town

    CorrespondingWater Quality

    Station

    (ACRWC)

    BASS

    Station

    Community

    Type(s) BASS Site ID

    Little Otter Creek M13-A North St New Haven LOC14.4 12.7 MF 540000000127

    Little Otter Creek M12-B Plank Rd New Haven LOC14.4 12.6 MF 540000000126

    Little Otter Creek M09-C Lime Kiln Rd Monkton LOC11 9.6 F 540000000096

    Little Otter Creek M09-A Monkton Rd Ferrisburgh LOC10 9.0 MF 540000000090

    Little Otter Creek M07-A Wing Rd Ferrisburgh LOC8 7 MF 540000000070

    Mud Creek T2.01-B Middlebrook Rd Ferrisburgh MDC1.2 0.7 F 540500000007

    ACRWC = Addison County River Watch Collaborative

    BASS = Biomonitoring & Aquatic Studies Section of VTDEC Water Quality Division

    MF = Macroinvertebrates & FishF = Fish

    Measurements of various metrics describing the health of fish and macroinvertebrate assemblages areused by the State of Vermont to determine aquatic life support use of wadeable stream reaches. Of theBASS stations listed above in Table 5, macroinvertebrate and fish data are available for stations 7, 9 and12.7, only. Station 7 (near site LOC8) was tested for fish and macroinvertebrates in 2006. Station 9(near LOC10) was tested for macroinvertebrates in 1990 and for fish in 1993. Station 12.7 (nearLOC14.4) was tested for fish in 1993 and for macroinvertebrates in 1996, 2001, and 2006. It appearsthat this Station 12.7 (and Station 4.1 near the Route 7 bridge and LOC4.3 outside of the reaches

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    assessed for this gemorphic study) are sampled for macroinvertebrates on an approximate 5-year cycle.Based on these limited sampling dates, macroinvertebrate communities were classified as ranging fromFair (or substantially degraded) to Excellent/ Very Good (near reference). For the sites wheremacroinvertebrate data is available for multiple dates, trends can be inferred. Biological integrity hasdecreased (from Excellent/ Very Good in 1996 to Good in 2006) at the upper watershed BASS station12.7 (near LOC14.4). An inconclusive trend is evident at BASS station 4.1 near the Route 7 crossing inthe lower main stem (from Fair in 1993, to Good in 2001 and 2006, back to Good/Fair in 2008).Individual metrics comprising the overall macroinvertebrate community assessments indicate thatdegraded conditions are due to nutrient enrichment and silt/sediment. Fish communities sampled atthese sites during discrete events in 1993 and 2006 indicate that moderately degraded, or goodbiological integrity exists at these BASS stations. (Fiske, 2011, personal communication).

    2.7 Land Use

    Current (1993) land use / land cover is summarized for the Little Otter Creek watershed in Table 6 andFigure 9. Land use is estimated as 51% agricultural, 25% forested, and 3% developed, with theremainder comprised of lakes, ponds, wetlands, and scrub/shrub (VCGI, 2003; Millette, 1997 source

    imagery dated 1991 to 1993).

    Forest cover is somewhat more abundant in the northeastern extremes of the watershed but overall ismuch lower than in other nearby watersheds (e.g., Lewis Creek, 61% forested). Agricultural land cover

    / land use dominates the watershed, particularly in the tributary of Mud Creek. Higher densities ofagricultural activities tend to be coincident with the silt and clay-rich soils of glaciolacustrine origin foundin the central and western portions of the watershed.

    In previous centuries, industrial and manufacturing activities were located along the Little Otter Creekmain stem (Smith, 1886; Beers, 1871). Saw mills, a grist mill, a potashery, a woolen factory and otherindustries were located in vicinity ofFrasers Falls (reach M02 / M01) near Ferrisburgh village. Similarenterprises operated in the later 1700s and early 1800s at Birketts Falls, Walkers Falls and above theMonkton Road crossing (Smith, 1886). Two sawmills, an iron ore furnace and casting house, and a

    distillery were operating upstream of the Plank Road / North Street intersection in New Haven during theearly to mid 1800s (Farnsworth, 1984). Dams were present on the channel to impound water andprovide power to these manufacturing interests. Most of these dams are no longer present, having beenbreached or destroyed in past floods. Dam remnants are present at Frasers Falls just above the LittleChicago Road crossing in Ferrisburgh village.

    In the last few centuries, 138 miles of roads have been installed within the Little Otter Creek watershed.A majority of the roads have drainage ditches associated with them. These roads and road ditchesintersect the stream network in more than 270 locations (Middlebury College Environmental StudiesSenior Seminar, 2011).

    The Vermont Railway line crosses Little Otter Creek near the Little Chicago Road crossing. This line was

    installed by 1850 (Farnsworth, 1984). Tributaries to the Little Otter including Mud Creek are crossed in

    several locations by this railroad line, as well as a former spur (constructed in 1891, now abandoned)leading from New Haven junction east to the village of Bristol. In some locations the tributaries have

    been channelized and floodplains reduced in width due to encroachment of the railroads.

    Widespread deforestation of Vermonts landscape occurred by the early- to mid-1880s to supportsubsistence farming, sheep farming and various lumber trades. Forest cover in the highlands began to

    regenerate in the late 1800s and early 1900s, during the industrial age when upland farms and sawmillswere commonly abandoned (Thompson & Sorenson, 2000).

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    Table 6. Land cover/ land use in Little Otter Creek watershed and Mud Creek tributary.

    Watershed

    Drainage Area

    (sq mi) Commercial/I

    ndustrial

    Resid

    ential

    Agric

    ultu

    ral

    Forest

    Water

    /Wetlan

    d

    Little Otter Ck (upstream of M01)

    (including Mud Creek) 72.5 0.03 3.2 55.2 25.4 13.5

    Little Otter Ck (upstream of M02)

    (including Mud Creek) 58.6 0.03 3.3 52.3 28.2 13.5

    Little Otter Ck (upstream of M05) 45.0 0.02 3.3 47.9 32.2 13.6

    Little Otter Ck (upstream of M09) 35.8 0.02 3.6 47.1 32.0 14.1

    Little Otter Ck (upstream of M13) 11.9 0.01 4.2 43.1 34.3 12.5

    Mud Creek (upstream of T2.01) 9.1 0.04 3.0 67.9 16.4 10.6

    Mud Creek (upstream of T2.03) 8.0 0.04 3.0 66.3 17.9 10.6

    Figure 9. Land cover / land use in the Little Otter Creek watershed.

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    2.8 Water Quality

    Long term water quality monitoring near the mouth of the Little Otter Creek has identified elevatedphosphorus levels and turbidity (VTDEC WQD and NYSDEC, 2009). Phosphorus loading targets have

    been established for tributaries draining to Lake Champlain as part of the strategy to achieve in-laketarget concentrations of phosphorus for various segments of Lake Champlain. Phosphorus loading fromthe Little Otter Creek to Lake Champlain for monitoring years 1990 to 2006 has exceeded target levels(Medalie & Smeltzer, 2004; LCBP, 2008). No significant trend (neither improving nor deteriorating) is

    apparent for phosphorus loading from the Little Otter Creek (LCBP, 2008). Little Otter Creek drains tothe Otter Creek segment of Lake Champlain, which has an established target concentration of

    14 micrograms per liter (VTANR & NYSDEC, 2002). Concentrations of phosphorus in the Otter Creeksegment of Lake Champlain are sometimes higher than this target, and sometimes lower; overall, there isno statistically significant trend in phosphorus levels in this lake segment (LCBP, 2008).

    Addison County River Watch Collaborative (ACRWC) has monitored water quality at the sub-watershed

    level since 1997. Sampling has been conducted during Summer-season, low- to moderate-flowconditions and more recently during Spring flow conditions. Monitoring has identified phosphorus and

    E. coliimpacts in Little Otter Creek, as well as sedimentation from unstable stream reaches, agriculturalrunoff, and road / culvert maintenance practices (ACRWC, 2009; ACRWC/ SMRC, 2011).

    Six stations are currently monitored by the ACRWC during Spring and Summer. Analyses are conductedfor E.coli, turbidity, total suspended solids, dissolved phosphorus, particulate phosphorus, and nitrates(Table 7). These ACRWC stations complement the long-term monitoring station maintained by VTDECWater Quality Division near the Route 7 bridge (vicinity of traditional ACRWC Site LOC4.3 Reach M02).

    Table 7. Water Quality stations monitored by the Addison County River WatchCollaborative (ACRWC) in Little Otter Creek watershed, 2010-2011.

    Stream Reach

    ACRWC

    Site No. Site Name

    M02 LOC4.3 Route 7 bridge

    Little Otter Creek M05 LOC7.8 Middlebrook Road bridge

    M07 LOC8 Wing Road bridge

    M09 LOC10 Monkton Road bridge

    M12 LOC14.4 Plank Rd west of North Street

    Mud Creek T2.01 MDC1.2

    Middlebrook Road bridge upstream from

    confluence with Little Otter Creek

    E. coliis frequently above the State water quality standard (77 organisms per 100 mL) at regularlymonitored sampling stations located from approximate river mile 4.3 to river mile 14.4 on the main stem

    and in the downstream end of Mud Creek (ACRWC, 2009; SMRC/ACRWC, 2011). Results for Summer of2010 sampling events are presented in Figure 10.

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    2010 - Little Otter CreekSummer E.coli Results (MPN/100 mL)

    1

    10

    100

    1000

    10000

    MDC1.2

    LOC14.4

    LOC10

    LOC8

    LOC7.8

    LOC4.3

    VT State Standard =

    77 MPN/100 mL

    Sampling

    Stations

    Date:

    DMF (cfs):

    Percentile:

    June 2

    18

    61%

    July 7

    12

    71%

    August 4

    71

    22%

    September 1

    7

    84%

    >2419.6

    Turbidity levels (suspended sediments) at the Little Otter Creek sampling stations LOC11, LOC7.8 andLOC4.3 and at the Mud Creek sampling station (ACRWC, 2009; SMRC/ACRWC, 2011) often exceed thestate standard of 10 Nephelometric Turbidity Units (NTUs) for this Class B cold-water stream (VermontNatural Resources Board, 2008) (see Figure 11).

    2010 - Little Otter CreekSpring/Summer Turbidity Results (NTUs)

    0.1

    1

    10

    100

    1000

    10000

    MDC1.2

    LOC14.4

    LOC10

    LOC8

    LOC7.8

    LOC4.3

    VT State Standard =

    10 NTUs

    Sampling

    Stations

    Date:

    DMF (cfs):

    Percentile:

    Apr 7

    86

    19%

    July 7

    12

    71%

    Aug 4

    71

    22%

    Sept 1

    7

    84%

    June 2

    18

    61%

    May 4/5

    67 / 107

    23%/ 16%

    Figure 11. Spring / Summer 2010 Turbidity Monitoring Results, Little Otter Creek watershed.

    Figure 10. Summer 2010

    E.coli monitoring results, Little

    Otter Creek watershed.DMF = Daily Mean Flow.Dates in blue indicatemoderate flows.

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    Total Phosphorus concentrations have often been above levels which would suggest nutrient enrichmentat the regularly-monitored sampling sites on the Little Otter main stem and Mud Creek (monitored 1997-2008, 2010). Long-term monitoring data collected by VTDEC Water Quality Division near the Route 7bridge (0.65 mile downstream of LOC4.3, monitored 1990-2009) suggest that phosphorus is moredominantly found in the dissolved phase rather than the particulate phase, sorbed to fine sediments(VTDEC WQD and NYSDEC, 2009; ACRWC, 2009).

    Total Phosphorus results for the Spring / Summer 2010 sampling events are summarized in Figure 12(SMRC/ACRWC, 2011). The mean concentration of Total Phosphorus for four Summer sample dates

    exceeded the proposed criteria of 44 ug-P/L for the warm-water medium gradient (WWMG) wadeablestream ecotype in Class B waters (VTDEC, 2009). Exceedance of these proposed criteria may indicateimpacts to aquatic life support and aesthetics uses.

    2010 - Little Otter Creek watershedSummer (low-flow) Total Phosphorus Results (ug/L)

    0

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    MDC1.2 LOC14.4 LOC10 LOC8 LOC7.8 LOC4.3

    MudCreek

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    Proposed In-stream Phosphorus Criteria = 44 ug/L (WWMG, Class B)

    Mud Creek tributary

    joins Little Otter Creek

    between sites LOC7.8

    and LOC4.3

    Figure 12. Spring / Summer 2010 Total Phosphorus Monitoring Results, Little Otter Creek watershed.

    There are no significantpointsources of phosphorus (such as wastewater treatment plant discharge)within the Little Otter Creek watershed (VTANR and NYSDEC, 2002); nonpointsources account for

    essentially the total contribution of phosphorus in the watershed. Eroding streambanks have beenidentified as a contributing nonpoint source of phosphorus in rivers and streams of Vermont (VTANR,2001; DeWolfe et al., 2004) and elsewhere in the nation (Kalma & Ulmer, 2003; Nelson & Booth, 2002).A study in nearby Lewis Creek watershed found that streambank erosion accounted for between 22 and35% of the total phosphorus load of that watershed (DeWolfe et al., 2004).

    Total Nitrogenconcentrations at ACRWC stations in the Little Otter Creek are historically low and belowthe state standard for nitrogen as nitrate (5 mg/L). In 2010, the mean concentration of Total Nitrogenfor the four Summer sample dates exceeded the proposed criteria of 0.75 mg-N/L for the warm-watermedium gradient (WWMG) wadeable stream ecotype in Class B waters suggesting possible impacts toaquatic life support and aesthetics uses.

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    Temperaturewas monitored at two stations on the Little Otter Creek (LOC14.4 and LOC10) during 2010as part of a separately-published flow study. Data loggers installed at these sites recorded temperature at15-minute intervals. Temperatures at both sites exceeded 20 degrees Celsius for several days during themid-Summer months. Temperature at downstream site LOC10 was consistently higher than upstreamsite LOC14.4 during July, August, and September. The Little Otter Creek channel between these sites ischaracterized by minimal forested buffers and extensive open-canopy wetlands.

    2010 - Little Otter CreekTemperature Monitoring (Celsius)

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    LOC10

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    Figure 13. Temperature Monitoring Results for Two Stationson the Little Otter Creek, Summer/Fall 2010.

    Based in part on VTDEC and ACRWC water quality monitoring results, the State of Vermont has listed thefollowing Little Otter Creek sections as impaired (VTDEC WQD, 2010a):

    Little Otter Creek main stem, 7.8 river miles upstream of the mouth, for aquatic life support dueto E. coliand other undefined pollutants resulting from agricultural runoff (reaches M01 through

    M05);

    Little Otter Creek main stem, from river mile 15.4 to 16.4, for aquatic life support and contactrecreation uses due to E.coliand other undefined pollutants resulting from agricultural runoff(reaches M12 and M13).

    In addition, the following river section is listed on Part C (List of Priority Surface Waters in need ofFurther Assessment) for E. coliimpacts (to contact recreation uses) likely from agricultural runoff (VTDEC

    WQD, 2010b):

    Mud Creek from the confluence with Little Otter Creek upstream approximately 4 miles (reachesT2.01 through T2.03).

    The Little Otter Creek is listed as a High priority for development of a Total Maximum Daily Load (TMDL)plan to address these water quality impacts (VTDEC WQD, 2010a).

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    3.0 ASSESSMENT METHODOLOGY

    Eleven reaches (12.7 river miles) of the Little Otter Creek and Mud Creek were evaluated to identify

    watershed- and reach-scale stressors that have led to sediment and nutrient impacts in the watershed asa result of modifications to the hydrologic and sediment regimes. This study utilized the VTANR guidancedocument, River Corridor Protection and Restoration Planning: A Guide for Project Identification andDevelopment(2010), as a framework for data evaluation and identification of mitigation projects.

    Assessments included:

    Windshield surveys of the watershed to visually observe channel / floodplain conditions duringhigh-water stages and identify points of concentrated stormwater runoff to the Little Otter Creek

    stream network (see Project CD for photographs); Aerial surveys of the watershed (25 March 2010, 7 April 2011); Remote-sensing (see Appendix G, Flow Accumulation Grid Maps); Phase 2 stream geomorphic assessments per VTANR protocols; A review of existing water quality data (VTDEC and ACRWC); and A review of existing flow data (USGS, ACRWC) A review of road and right-of-way impacts by Middlebury College students.

    Three Steering Committee meetings with project sponsors (VTDEC MAPP and RMP) and variousstakeholders were convened during this study to share data and identify projects for implementation.

    A list of Steering Committee members is provided on page ii of this report. Meeting summaries areprovided on the Project CD.

    3.1 Phase 2 Stream Geomorphic AssessmentPhase 2 Stream Geomorphic Assessments and Bridge and Culvert Assessments conducted on the LittleOtter Creek and Mud Creek reaches utilized protocols published by the Vermont Agency of NaturalResources (2009) and available at:http://www.vtwaterquality.org/rivers/htm/rv_geoassesspro.htm.

    Reference is made to these protocols for a description of specific methods.

    Phase 2 Stream Geomorphic Assessment protocols are field procedures for geomorphic and habitatassessment. Reach-specific and cross-section data gathered during Phase 2 characterize the present

    geomorphic condition of the river reach and the dominant process(es) of adjustment (i.e., degradation,widening, aggradation and/or planform adjustment). Phase 2 results, along with Phase 1 assessmentresults, define the natural and human disturbances to the watershed and channel over time and the

    composite response or adjustment of the channel to these stressors (i.e., the degree of departure).

    The eleven Little Otter Creek / Mud Creek reaches were assessed from 14 May through 28 October 2010.Specific features and channel positions were located using a GarminTM 76CSx model global positioning

    system (GPS) unit. Pictures were recorded with a digital camera.

    In accordance with protocols, select features were digitized in ArcView 3.x and referenced to theVermont Hydrography Dataset (VHD), using the Feature Indexing Tool, a component of the StreamGeomorphic Assessment Tool (SGAT, v. 4.59). Certain parameters documented during the original

    Phase 1 Stream Geomorphic Assessment were updated based on field observations in Phase 2 (seeSection 3.2). Phase 2 assessment data were entered into the online Data Management System (DMS,v.4.56) maintained by the VTANR. Phase 2 reach summary reports are compiled in Appendix A.

    http://www.vtwaterquality.org/rivers/htm/rv_geoassesspro.htmhttp://www.vtwaterquality.org/rivers/htm/rv_geoassesspro.htmhttp://www.vtwaterquality.org/rivers/htm/rv_geoassesspro.htmhttp://www.vtwaterquality.org/rivers/htm/rv_geoassesspro.htm
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    Five road crossing structures, two footbridges, and two instream culverts were encountered during Phase2 assessments. Spans, clearance and width measurements were conducted at each structure. The spanof each crossing was compared to measured or predicted bankfull widths (VTDEC WQD, 2006) todetermine if the structure was a constrictor of flows at the bankfull stage or the flood-prone-widthelevation (10-year to 50-year flood). Appendix B of this report provides a summary of the bridge andculvert assessments completed for the bridge and culvert crossings in accordance with Appendix G of theVTANR protocols (April 2009). Bridge and culvert data were entered into the Structures portion of the

    DMS (under the Little Otter Creek database).

    A reference stream type (Phase 1) and an existing stream type (Phase 2) were classified for each reach.Stream type designations are based on Rosgen (1996) and Montgomery & Buffington (1997). Asensitivity classification was also assigned to each reach based on the Phase 2 stream geomorphic

    assessment data. According to VTANR protocols, the sensitivity classification is intended to identify thedegree or likelihood that vertical and lateral adjustments (erosion) will occur, as driven by natural and/or

    human-induced fluvial processes (VTANR, 2007b). Inherent in the stream sensitivity rating are:

    the natural sensitivity of the reach given the topographic setting (confinement, gradient) andgeologic boundary conditions (sediment sizes) as reflected in the reference stream typeclassification; and

    the enhanced sensitivity of the reach given by the degree of departure from reference (ordynamic equilibrium) condition as reflected in the existing stream type classification and thecondition (Reference, Good, Fair to Poor) rating of the Rapid Geomorphic Assessment).

    Abbreviations used in the sections below include the following (see protocols for further description):

    Left Bank, facing downstream (abbreviated, LB) Right Bank, facing downstream (RB). Incision Ratio (IR) = Low Bank Height / Bankfull Max Depth

    o IRRAF = Recently Abandoned Floodplain Incision Ratioo

    IRHEF = Human-Elevated Floodplain Incision Ratio

    Entrenchment Ratio (ER) = Flood Prone Width / Bankfull Width Width / Depth Ratio (W/D) = Bankfull Width / Mean Depth Flood Prone Width (FPW) estimated as the 10- to 50-year flood event Stream Type Departure (STD) Large Woody Debris (LWD) Debris Jams (DJs) Rapid Geomorphic Assessment (RGA) Rapid Habitat Assessment (RHA) Vermont Hydrography Dataset (VHD) National Wetlands Inventory (NWI) Vermont Significant Wetlands Inventory (VSWI)

    3.2 Phase 1 Assessment UpdatesOriginal Phase 1 assessment data (ACRPC, 2006) for the eleven tributary reaches were reviewed and

    verified during field work as per VTANR protocols. Necessary corrections or updates were documentedon Phase 1 summary sheets for each reach. As appropriate, GIS shape files were corrected or updated(using the Feature Indexing Tool). Phase 1 data in the DMS was updated, and the metadata for eachPhase 1 step in the database were reviewed and updated (where necessary) to reflect that data weresupported by field observations. Phase 1 reach summary reports are presented in Appendix A. Phase 1steps that were updated included:

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    reach break elevations (Step 2.1) valley confinement (Step 2.9) reference stream type (Step 2.11) presence of alluvial fans (Step 3.1); presence and location of bedrock or other grade controls (Step 3.2) steepness of valley side slopes (Step 3.4); width of riparian buffers (Step 4.3); groundwater inputs (Step 4.4); revetment lengths and locations (Step 5.3); channel straightening (Step 5.4); location and lengths of berms and roads (Step 6.1); location and lengths of development (Step 6.2); occurrence of depositional bars and bedforms (Step 6.3); occurrence of channel avulsions, neck cut-offs, flood chutes (Step 6.4); erosion lengths and heights (Step 7.2); occurrence of, or potential for, ice/debris jams (Step 7.3)

    The elevation data for the downstream and upstream ends of the overall reach were originally developedin the Phase 1 assessment (Step 2.1) of the Little Otter Creek watershed (ACRPC, 2006). During thisPhase 2, nearly all the reach break elevations were updated as a result of field-based observations, andto correct apparent interpolation errors. Accordingly, channel and valley gradient calculations wereupdated. In no case did these updates result in a change in stream type slope category for the overallreach.

    The position of the reference (Phase 1) valley walls was updated, based on field observations andfollowing clarifications to valley wall delineation procedures articulated in protocol updates between 2004and 2009. Also, a shape file of the modified (Phase 2) valley wall was generated; details of the valleywall delineation method are provided in Appendix C. Updated valley wall shape files are contained on theProject CD.

    3.3 Quality Assurance / Quality ControlPhase 1 and Phase 2 stream geomorphic data were reviewed against standard DMS Phase 2 quality

    control checks (X.1 through X.4), and then submitted to the River Management Section for a qualityassurance review. Quality assurance documentation is contained in Appendix D.

    The following considerations and limitations apply to the Phase 2 data for the Little Otter Creek / MudCreek reaches:

    Where applicable, reaches were segmented using the Segmentation Tool contained in SGAT(v. 4.59). Segmentation was necessary to:

    o Capture subreaches of a stream type (after Montgomery & Buffington, 1997; and Rosgen, 1996)that was different than the reference stream type of the overall reach;

    o Identify sections of a reach that were of distinctly different geomorphic condition;o Identify sections of a reach undergoing a different channel management or land use; ando Define wetland-dominated and/or beaver-impounded channel sections.The Segmentation Tool within SGAT automates the calculation of segment lengths. Elevation data

    for the downstream and upstream segment breaks were interpolated from USGS 7.5-Minutetopographic maps. Segment lengths and elevations are presented in Appendix E, along with channel

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    gradients calculated for each segment. Segment slopes were factored into the stream-typedesignation for each segment.

    Select Phase 2 features (including, grade control locations, stormwater inputs, streambank erosion,revetment locations, and more) were geo-located using the Feature Indexing Tool (FIT) in SGAT.Using FIT, these features are indexed to the available Vermont Hydrography Dataset (VHD) for the

    Little Otter Creek watershed. The VHD in this region was apparently digitized from 1995orthophotos. In a few cases, surface waters depicted on the VHD were offset from their actualposition on 1995 orthophotos available for the study area. In some cases, the actual channelposition has moved from its 1995 position as a result of natural channel migrations. These caseswere revealed by comparison of the 1995 orthophotos with available 2003 and 2006 imagery, or by

    review of 2010 channel positions recorded with a hand-held GPS receiver. Thus, locations andlengths of features indexed to the VHD should be considered approximate.

    Most of the assessed segments of the Little Otter Creek / Mud Creek could be classified assuspended-load channels (Schumm, 1977) or washload-dominated channels (Knighton, 1998).These channels, flowing through cohesive silts of glaciolacustrine origin, were dominated by

    suspended loads of finer materials. Bedloads of coarser sands, gravels or cobbles were generallyabsent (with exception of a few segments). Cross sections performed in these silt/clay bed channelstended to be somewhat narrower and significantly deeper than predicted by the VTANR regional

    hydraulic geometry curves which have been developed for non-cohesive alluvial (gravel- and sand-bed) streams (VTDEC WQD, 2006b; VTDEC WWD, 2001). This finding is consistent with Schumm(1960), who reported a decrease in width/depth ratios with increasing percentage of silt and claysediments in channel bed and banks.

    4.0 PHASE 2 ASSESSMENT RESULTS

    Geomorphic and habitat assessments were completed on 11 reaches (12.7 river miles) of the Little Otter

    Creek and Mud Creek in 2010. Assessment results are discussed below in Sections 4.1 and 4.2,respectively. Reach evaluations have also been informed by observations during windshield surveys andflyovers of the watershed. Reach and segment summary reports are provided in Appendix B. Detailedreach narratives are provided in Appendix F. Reach locations are illustrated in Figure 14.

    4.1 Little Otter Creek main stem - New Haven, Monkton, Bristol

    Main stem assessements focused on ten reaches in the central portion of the Little Otter Creekwatershed, from Plank Road in New Haven downstream to the Satterly Road crossing in Ferrisburgh(Figure 14), These reaches (M13 through M04) have upstream drainage areas ranging from 11.9 to 57.4square miles. Assessment results are summarized in Table 8.

    For the most part, assessed reaches of the Little Otter Creek main stem are characterized by a sinuous,

    low-gradient, channel in a very broad, unconfined valley setting. With a few exceptions, the planform ofthe river has remained largely unchanged for at least 70 years, based on review of historic aerialphotographs (2006, 2003, 1995, 1974, 1962, 1942). The channel is well-connected to the surrounding

    floodplain. Streambanks are comprised of cohesive sediments (silt and silty-clays). Floodplain soils arehydric in na