a study of bank erosion rates within …a study of bank erosion rates within selected reaches of the...

A Study of Bank Erosion Rates within

Selected Reaches of the Housatonic River

Prepared by

Stantec Consulting 30 Park Drive

Topsham, ME 04086

August 27, 2009

A STUDY OF BANK EROSION RATES WITHIN SELECTED REACHES OF THE HOUSATONIC RIVER

Table of Contents

1.0 Introduction ....................................................................................................................... 1 2.0 Methodology ...................................................................................................................... 1 3.0 Results .............................................................................................................................. 8 4.0 Summary ......................................................................................................................... 12 5.0 Literature Cited ................................................................................................................ 12

List of Figures Figure 1. Primary Study Area Figure 2. Example BEHI Form Figure 3. Example NBS Form Figure 4. North Carolina Piedmont Region Bank Erosion Prediction Curve Figure 5. South Central Colorado Region Bank Erosion Prediction Curve Figure 6. Bank Erosion Rate Predictions for Locations along Reaches 5A and 5B Figure 7. Cumulative Bank Erosion for Reaches 5A and 5B Figure 8. Reaches 5A and 5B Bank Erosion Prediction: Example GIS Shapefile Showing

Bank Segments

List of Appendices Appendix A Aerial Images Appendix B Representative Bank Photographs Appendix C CD Containing Two Shapefiles

Project Number 195600459

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1.0 INTRODUCTION

The United States Environmental Protection Agency (USEPA) is in the process of reviewing General Electric’s (GE) Housatonic River – Rest of River Corrective Measures Study (CMS; GE 2008). Some of the alternatives presented in the CMS involve removal of contaminated river bank soil with subsequent bank restoration using a variety of methods that range from armoring with stone to using vegetation and some stone to stabilize reconstructed banks. A reconnaissance-level bank erosion study was conducted to estimate on-going erosion, which will facilitate USEPA review of the CMS and the proposed alternatives.

Streambank erosion rates can be predicted using the Bank Assessment for Non-Point Source Consequences of Sediment (BANCS; Rosgen 2006). The BANCS method provides an estimate of the rate of erosion and the amount of bank material being released from streambanks into the river system. It is a visual assessment tool that, when combined with more quantitative studies completed in other states, can provide a reasonable estimate of erosion rates. The BANCS method uses two bank erodibility estimation tools: the Bank Erosion Hazard Index (BEHI) and Near Bank Stress (NBS). The application involves evaluating the bank characteristics and flow distribution along river reaches, mapping the location and extent of each bank feature, and developing risk ratings per bank feature. In each reach of river or stream an overall estimate of erosion is made by multiplying the length and height of each bank type by the specific bank erosion term, and then summing the estimates of erosion. This provides an estimate of cubic yards and/or tons of sediment that erode per reach per year.

2.0 METHODOLOGY

During the week of May 18, 2009, bank erosion surveys were performed on the Housatonic River in Reach 5A and Reach 5B as indicated in Figure 1. Qualitative surveys were also conducted upstream between areas previously restored by GE and USEPA up to the TJ Maxx Plaza on Merrill Road in Pittsfield. In Reaches 5A and 5B data were collected from approximately 41,000 linear feet of stream channel and 82,000 feet of streambank (i.e., both banks were surveyed). Field surveys of bank erosion were stopped near the end of Reach 5B because the BEHI and NBS values began to decline due to the backwater effect of Woods Pond.

To ensure that the field data would be collected during a representative period of flow, recent flow data for two gauges on the Housatonic River were compared to long-term averages. It was decided to proceed with the data collection because flows were close to average and no significant rainfall events were predicted. After the field data were collected, the flow data for the study period were also compared with the historical average to verify that flows had remained average.

DRAFT CONFIDENTIAL FOIA EXEMPT ATTORNEY CLIENT PRIVILEGED

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During field surveys, the left and right banks of Reach 5A and most of Reach 5B were classified based on both the BEHI and NBS. Figures 2 and 3 show example BEHI and NBS data forms, respectively. As part of classification, banks were divided into segments and inventoried based on the changes of physical bank characteristics and the applied shear stress, e.g., bank height, root depths, root density, bank angle, and amount of surface protection. The locations of bank segments and sampling locations were marked on aerial photographs during the field survey (Appendix A). Representative photographs of banks (Appendix B) were taken to visually document BEHI conditions and factors contributing to NBS.

In the BANCS model there are seven methods that can be used to assess energy distribution against streambanks, which is referred to as NBS. Methods 2, 3, and 5 were used during this survey to measure NBS. Method 2, which is completed in the field and then verified using aerial photography, involves measuring the river’s radius of curvature and dividing that value by the bankfull width. Method 3 is completed in the field and involves measuring the slope of pools in the river and the average slope of the river, then calculating the ratio of pool slope to average slope. Method 5 uses cross-section data to calculate the ratio of near-bank maximum depth to bankfull mean depth. Cross-sections previously collected for the EPA Housatonic River modeling study were used for Method 5.

The location of the thalweg was mapped in the field on aerial photos to provide another indication of NBS (Appendix C). A survey-grade geographic positioning system (GPS) unit was used to verify the length of bank segments and determine locations along the river. The GPS data were loaded into AutoCAD and converted to a spatially-referenced ArcView shapefile (NAD83 MA projection). The thalweg location and the existing cross-sections were used to assign an NBS value to each bank location throughout the study reaches.

The BEHI and NBS numbers for each of the 1,910 bank segments (shown in Appendix C) of Reaches 5A and 5B were converted to bank erosion rates using graphs of curves for the North Carolina Piedmont Region (North Carolina State University Stream Restoration Program 1989) and the South Central Colorado Region (USEPA 1989; Figures 4 and 5, respectively). It should be noted that, based on soil cohesion and vegetation type, it is expected that the South Central Colorado Region curve will over-predict bank erosion and the North Carolina Piedmont Region curve will under-predict bank erosion for the Housatonic River. To facilitate interpretation of the data, the field data were digitized, loaded into AutoCAD, and converted to a spatially-referenced ArcView shapefile (NAD83 MA projection) to show the bank erosion rates for Reaches 5A and 5B.


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Stream:

Station:

Date: 5-19-2009 C4/5 VIII

Study Bankfull Bank Height

Height (ft) = (ft) =

Root Study Depth Bank

(ft) = Height (ft) =

Root Density ( F ) x ( E ) =

as % =

Bank Angle

as Degrees =

Surface Protection

as % = Bank Material Adjustment:

Sand (Add 10 points) Silt/Clay (no adjustment)

Very Low Low Moderate High Very High Extreme and

5 – 9.5 10 – 19.5 20 – 29.5 30 – 39.5 40 – 45 46 – 50

BEHI Score (Fig. 3-7)

16

0.5

9

Root Depth / Study Bank Height ( E )

0.03125 16

5

Weighted Root Density ( G )

25%

41

9

9

7

Valley Type:

Stratification Adjustment

Adjustment Bank Material

Study Bank Height / Bankfull Height ( C )

Cobble (Subtract 10 points if uniform medium to large cobble)

Stream Type:

( D ) / ( A ) =

20%

Boulders (Overall Low BEHI)

Housatonic Example Bank Uptream of Holmes Road DAB Observers:

Location: Example Bank for Report

Total Score

3.2( A ) / ( B ) =

Adjective Rating

Bank Angle ( H )

0.00781

Gravel or Composite Matrix (Add 5–10 points depending on percentage of bank material that is composed of sand)

7

0

85

Surface Protection ( I )

0

Bedrock (Overall Very Low BEHI)

Add 5–10 points, depending on position of unstable layers in relation to bankfull stage

(G)

(E)

(H)

( I )

(C)

Bank Sketch

0 1 2 3 4 5 6 7 8 9

10 11 12

0 1 2 3 4 5 6

Horizontal distance (ft)

Vert

ical

dis

tanc

e (ft

) Bank Angle

(H)

Root Depth

(D)

STU

DY

BA

NK

Hei

ght

(A)

Sur

face

P

rote

ctio

n (I)

Start of

Bank

Bankfull

BA

NK

FULL

H

eigh

t (B

)

(A)

(A)

(F)

(D)

(B)

Figure 2. Example BEHI Form


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Stream: Location: Station: Stream Type: Valley Type: Observers: Date:

Level I

Level II Level II

Level II

Level III

Level III Level IV

(1) (2) (3) (4) (5) (6) (7) N / A > 3.00 < 0.20 < 0.40 < 1.00 < 0.80 < 0.50 N / A 2.21 – 3.00 0.20 – 0.40 0.41 – 0.60 1.00 – 1.50 0.80 – 1.05 0.50 – 1.00 N / A 2.01 – 2.20 0.41 – 0.60 0.61 – 0.80 1.51 – 1.80 1.06 – 1.14 1.01 – 1.60 See 1.81 – 2.00 0.61 – 0.80 0.81 – 1.00 1.81 – 2.50 1.15 – 1.19 1.61 – 2.00 (1) 1.50 – 1.80 0.81 – 1.00 1.01 – 1.20 2.51 – 3.00 1.20 – 1.60 2.01 – 2.40

Above < 1.50 > 1.00 > 1.20 > 3.00 > 1.60 > 2.40

Near-Bank Max Depth

dnb (ft)

Riffle Slope Srif

Pool Slope Sp

Example

Bankfull Shear

Stress τbkf ( lb/ft2 )

Near-Bank Stress (NBS)

Ratio τnb / τbkf


Mean Depth dbkf (ft)


(5)

(6)

Housatonic River

Ratio dnb / dbkf


Near-Bank Slope Snb

Near-Bank Shear

Stress τnb ( lb/ft2 )

Near-Bank Max Depth

dnb (ft)

(5) Ratio of near-bank maximum depth to bankfull mean depth ( dnb / dbkf )……………..……


Methods for Estimating Near-Bank Stress (NBS)

(7) Velocity profiles / Isovels / Velocity gradient…………………………………....………...….

Near-Bank Stress

Leve

l III

Ratio Sp / Srif

Mean Depth dbkf (ft)

Average Slope S

Ratio Sp / S

Leve

l I

(1)

Radius of Curvature

Rc (ft)

Bankfull Width Wbkf

(ft)

Estimating Near-Bank Stress ( NBS )

Leve

l II

(2)

(3)

(4)

Ratio Rc / Wbkf


Dominant Pool Slope Sp

Average Slope S

(6) Ratio of near-bank shear stress to bankfull shear stress ( τnb / τbkf ).…...……...........….

Reconaissance

General prediction

(1) Channel pattern, transverse bar or split channel/central bar creating NBS...……..

(2) Ratio of radius of curvature to bankfull width ( Rc / Wbkf )…………………...……………………

General prediction

General prediction

Detailed prediction

Detailed prediction

Low Moderate

Near-Bank Stress (NBS) ratings

(7)

Method number

Very Low

Converting Values to a Near-Bank Stress (NBS) Rating

Leve

l IV

Velocity Gradient ( ft / sec / ft )

High Very High Extreme

Overall Near-Bank Stress (NBS) rating

DAB

……………...….NBS = High / Very High Extensive deposition (continuous, cross-channel)……………..……………...……. Chute cutoffs, down-valley meander migration, converging flow……………………

…………....NBS = Extreme ………….….NBS = Extreme

Transverse and/or central bars-short and/or discontinuous……….…

(3) Ratio of pool slope to average water surface slope ( Sp / S )…………...…...…….....…….

(4) Ratio of pool slope to riffle slope ( Sp / Srif )………..……...…………..………………..…….

Validation

Figure 3. Example NBS Form


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North Carolina Streambank Erodibility Produced by NRCS and NCSU

100

10

1

0.1

0.01

0.001

y = 0.6060e0.4624x

R2 = 0.9197

y = 0.3769e0.2212x

R2 = 0.6683

y = 0.0023e0.9579x

R2 = 0.9256

y = 0.0564e0.3222x

R2 = 0.5376

1 2 3 4 5 6 7 Very Low Low Moderate High Very High Extreme

Ban

k Er

osio

n R

ate

(ft/y

r)

Near Bank Stress Index

Moderate BEHI High BEHI Very High BEHI Extreme BEHI

Expon. (Extreme BEHI) Expon. (Very High BEHI) Expon. (Moderate BEHI) Expon. (High BEHI)

Figure 4. North Carolina Piedmont Region Bank Erosion Prediction Curve


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Prediction of Annual Streambank Erosion Rates using Colorado USDA Forest Service (1989) data for streams found

in sedimentary and/or metamorphic geology

Low Moderate High Extreme Very Low Very High

MODERATE BEHI BER = 0.0556e0.5057(NBS)

LOW BEHI BER = 0.0082e0.7349(NBS)

HIGH & VERY HIGH BEHI

BER = 0.109e0.4159(NBS)

EXTREME BEHI BER = 0.0642e0.9391NBS

0.01

0.1

1

10

0 1 2 3 4 5 6 7 Near-Bank Stress (NBS)

Ban

k Er

osio

n R

ate

(BER

) in

ft / y

r

Figure 5. South Central Colorado Region Bank Erosion Prediction Curve


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3.0 RESULTS

The average mean daily flow for the May 18 to May 22, 2009, survey period based on data from the East Branch of the Housatonic River US Geological Survey (USGS) gauge located at Coltsville, MA (upstream of the study area) was 103 cubic feet per second (cfs). This average was calculated from daily flow data downloaded from the gauge for the period of May 18 to May 22. This compared well with the long-term (72-year) average of 138 cfs for the month of May for the Coltsville station. The average flow for the survey period calculated from data downloaded from the USGS gage located near Great Barrington, MA (downstream of the study area) was 545 cfs. This compared well with the long-term (95-year) average of 676 cfs for the Great Barrington station. Flows during the study period were slightly below average but were representative.

The 1,910 bank segments inventoried ranged from 2 to 271 feet in length and had an average length of 43 feet.

The curves shown in Figures 4 and 5 were used to estimate yearly bank erosion based on BEHI and NBS values generated from the field survey. An average bank erosion rate of 0.32 feet/year was calculated for Reaches 5A and 5B. This is two orders of magnitude higher than the rates of 0.001-0.005 feet/year documented for stable streams in similar valley systems in North Carolina (unpublished data). Even when one considers that the North Carolina rivers probably have lower rates of bank erosion than rivers in the northeast, the data from the Housatonic clearly indicate that Reaches 5A and 5B are in a state of accelerated bank erosion. Qualitative surveys also indicate that upstream banks between areas previously restored by GE and USEPA up to the TJ Maxx Plaza on Merrill Road in Pittsfield are in a state of extreme erosion.

The BEHI and NBS numbers for the 1,910 bank segments were converted to sediment in tons/foot/year by multiplying bank erosion rates (North Carolina and Colorado) by the bank height and the length of bank assessed. The volume of material (cubic feet) lost from the streambank each year was converted to pounds based on a density of 124 pounds/cubic foot (lbs/cft).1 The values were then normalized to reflect the weight of sediment eroding for each foot of streambank.

Figure 6 shows the bank erosion in tons/foot/year for Reaches 5A and 5B, which varies from almost 0 to 1.6 tons/foot/year with an average rate of about 0.2 tons/foot/year.

1 Density estimated based on a particle density of 165 lbs/cft and bulk density of a sand soil of 105 lbs/cft (Jury and Horton 2004).


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Reach 5 Housatonic River Bank Erosion Rate Prediction

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Ban

k Er

osio

n (to

ns/ft

/yr)

0 5000 10000 15000 20000 25000 30000 35000 40000 45000

STA Downstream of Confluence (ft)Bank Erosion Rate Colorado Prediction Bank Erosion Rate NC Prediction Linear (Bank Erosion Rate NC Prediction) Linear (Bank Erosion Rate Colorado Prediction)

Figure 6. Bank Erosion Rate Predictions for Locations along Reaches 5A and 5B

The total bank erosion predicted from the 82,000 linear feet of streambank (41,000 feet of stream channel) surveyed was estimated to be about 8,500 tons/year using the South Central Colorado Region curve and 6,200 tons/year using the North Carolina Piedmont Region curve (Figure 7). The actual rate is likely between these two rates. The rates are based on a number of conditions, such as soil cohesion and vegetation, which are different depending on location. The conditions in Colorado lead to higher rates of erosion compared to the conditions in North Carolina. The conditions found along the Housatonic River are somewhere between the conditions found in North Carolina and Colorado, leading to the conclusion that erosion rates would be between those calculated.


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Reach 5 Housatonic River Cumulative Bank Erosion Prediction

10000

9000

8000

7000

on/y

r)

6000

sion

(T

5000

ativ

e B

ank

Ero

4000

1000

2000

3000

Cum

ul

Cumulative Bank Erosion NC Prediction = 0.1303 * STA + 829.23

Cumulative Bank Erosion CO Prediction = 0.2069 * STA + 181.32

0 0 5000 10000 15000 20000 25000 30000 35000 40000 45000

STA Downstream of Confluence (ft) Cumulative Bank Erosion Colorado Prediction Cumulative Bank Erosion NC Prediction Linear (Cumulative Bank Erosion NC Prediction) Linear (Cumulative Bank Erosion Colorado Prediction)

Figure 7. Cumulative Bank Erosion for Reaches 5A and 5B Note: The straight, dashed “linear” lines represent the linear cumulative trend for total bank erosion. The slopes of each of these lines are the average bank erosion rates per unit length for each bank erosion prediction. These lines show that the two different predictions have two separate average bank erosion rates and the areas that graphically have a higher than average bank erosion rate (i.e., slope of the cumulative curve).

The geographic information system (GIS) analysis supports the field data and observations. Reaches 5A and 5B have areas of very low bank erosion and areas of extreme accelerated bank erosion. The GIS analysis, however, shows that the areas of high bank erosion are generally out of phase with the plan form of the river. In alluvial systems, the areas of highest erosion are expected to occur in the lateral scour pools on the outside of the meander bends and in the lower third of the meander bend. On the reaches studied here, many of the extreme and very high bank erosion rates are located upstream of point bars on the inside banks. This is a sign of active channel migration and horizontal instability. The shapefile created for the GIS analysis can be mapped or displayed over aerial photography or other base map information (Figure 8). The shapefile has an associated database file containing data on the 1,910 segments.


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Housatonic Bank Erosion Prediction

0.0000 - 0.0001 tons/yr

0.0001 - 0.25 tons/yr

0.25 - 1.0 tons/yr

1.0 - 10.0 tons/yr

º 10.0 - 50.0 tons/yr 50.0 - 232 tons/yr Miles

0 0.25 0.5 1

Figure 8. Reaches 5A and 5B Bank Erosion Prediction:

Example GIS Shapefile Showing Bank Segments


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4.0 SUMMARY

Streambank erosion rates for Reaches 5A and 5B of the Housatonic River were assessed in May 2009 during a period of average flow using a combination of the BEHI and NBS methods. BEHI provides an indication of streambank susceptibility to erosion, while NBS provides an indication of the erosive forces acting on the streambank. Together, these two factors provide a fairly good indication of streambank erosion. In total, the streambanks were divided into 1,910 segments based on their BEHI and NBS scores. Using quantitative studies from North Carolina and Colorado, the BEHI and NBS scores were converted to erosion rates that averaged 0.32 feet/year over the two reaches surveyed. Stable alluvial streams generally demonstrate erosion rates of 0.001 to 0.005 feet/year. Based on this comparison, Reaches 5A and 5B of the Housatonic River are in a state of accelerated bank erosion.

When combined with measurements of streambank height, the rates of erosion can be converted into a weight of sediment reaching the river. This works out to be approximately 0.16 tons/foot/year or approximately 7,300 tons/year for these two reaches. A GIS analysis revealed that many of the extreme and very high bank erosion rates were located upstream of point bars on the inside banks, a sign of active channel migration and horizontal instability.

5.0 LITERATURE CITED

Colorado USDA Forest Service. 1989. Data for Streams in Sedimentary and/or metamorphic geology.

GE. 2008. Housatonic River – Rest of River Corrective Measures Study. March 2008. General Electric Company, Pittsfield, MA.

Jury, W. A. and R. Horton. 2004. Soil Physics (6th Edition). John Wiley and Sons, Inc.

North Carolina State University Stream Restoration Program. 1989. North Carolina Piedmont Region Bank Erosion Prediction Curve. Available online at http://www.bae.ncsu.edu/ programs/extension/wqg/srp/.

Rosgen, D. 2006. Watershed Assessment of River Stability and Sediment Supply (WARSS). Wildland Hydrology, Fort Collins, Colorado. Copyright 2006. Details can be accessed online at http://www.epa.gov/warsss/pla/box08.htm.

USEPA. 1989. South Central Colorado Region Bank Erosion Rating Curve. Available online at http://www.epa.gov/warsss/pla/box08.htm.


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http://www.epa.gov/warsss/pla/box08.htmhttp://www.epa.gov/warsss/pla/box08.htmhttp:http://www.bae.ncsu.edu


APPENDIX A Aerial Images


APPENDIX B Representative Bank Photographs


Example of bank conditions with a Bank Erosion Hazard Index (BEHI) rating of very low

Example of bank conditions with a BEHI rating of low


Example of bank conditions with a BEHI rating of moderate

Example of bank conditions with a BEHI rating of high


Example of bank conditions with a BEHI rating of very high

Example of bank conditions with a BEHI rating of extreme


APPENDIX C CD Containing Two Shapefiles:

The thalweg and data for the 1,910 segments.

REPOSITORY TARGET SHEET

US EPA New England Superfund Document Management System /

RCRA Document Management System Native Files Target Sheet

SDMS Document ID #:517636

Site Name: GE HOUSATONIC RIVER

File Type(s) Attached (examples: Excel file or .jpg): cpg, dbf,dwg, idx, shp and shx

Document Type this Target Sheet Represents:

[ ] Map [ ] Photograph [ ] Graph/Chart

[ ] Video [ ] Compact Disc [ x] Other (Specify below)

Description or Comments: Various Housatonic Bank Erosion Prediction files from 07-25-09

To view the attached files, open the “Attachment Panel”

by clicking on the paper clip - - at the bottom left of this window.

** Please note to view attachments the software corresponding with the specified file type is necessary. **

For any additional assistance please contact the EPA New England Office of Site Remediation and Restoration Records and Information Center-

Telephone (617) 918 1440

1252;LC_CTYPE=English_United States.1252;LC_MONETARY=English_United States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

COATYRNCATYRBANKHEIGHTBANK_IDBEHIRATINGCOBERLAYERLENGTHOFBALOCATIONNBSRATINGNCBERZONE0.2026910000000000.00000000000000051910.000000000000000Low0.035950200000000C-STRM-BEHI-LOW18.1845144000000001.0000000000000002.0000000000000000.0000000000000001.000000000000000

0.2458694000000000.10684460000000061909.000000000000000Low Mod0.035950200000000C-STRM-BEHI-LOW_MOD18.3819015000000001.0000000000000002.0000000000000000.0156225000000001.000000000000000

1.1863779000000000.83376040000000061908.000000000000000Mod High0.152869300000000C-STRM-BEHI-MOD_HEIGH20.8588245000000001.0000000000000002.0000000000000000.1074332000000001.000000000000000

2.4193167000000000.00000000000000041907.000000000000000Low0.035950200000000C-STRM-BEHI-LOW271.3125619000000001.0000000000000002.0000000000000000.0000000000000004.000000000000000


32.956563400000000231.185990000000000151905.000000000000000Very High Extreme0.872051000000000C-STRM-BEHI-VH-EX40.6300218000000001.0000000000000005.0000000000000006.1173238000000003.000000000000000

9.7042854000000003.45177590000000061904.000000000000000High Mod0.575332400000000C-STRM-BEHI-HEIGH_MOD45.3348079000000001.0000000000000004.0000000000000000.2046434000000003.000000000000000

0.0000000000000000.00000000000000021903.000000000000000Very Low0.000000000000000C-STRM-BEHI-VERY_LOW12.2144753000000001.0000000000000004.0000000000000000.0000000000000003.000000000000000

0.0000000000000000.00000000000000031902.000000000000000Very Low Low0.000000000000000C-STRM-BEHI-VL_L24.2347965000000001.0000000000000001.0000000000000000.0000000000000002.000000000000000

16.4251014000000005.31978030000000061901.000000000000000High0.872051000000000C-STRM-BEHI-HEIGH50.6236208000000001.0000000000000005.0000000000000000.2824409000000002.000000000000000


1.1866218000000000.07715310000000061899.000000000000000Mod0.092192900000000C-STRM-BEHI-MOD34.5940830000000001.0000000000000001.0000000000000000.0059943000000003.000000000000000






6.18137100000000014.48005380000000061893.000000000000000Very High0.250422100000000C-STRM-BEHI-VERY_HEIGH66.3436220000000001.0000000000000002.0000000000000000.5866216000000004.000000000000000








3.0122447000000000.76049290000000061885.000000000000000Mod Low0.420306100000000C-STRM-BEHI-MOD_LOW19.2624534000000001.0000000000000004.0000000000000000.1061135000000002.000000000000000















21.05743890000000033.417706900000000151870.000000000000000Very High High0.575332400000000C-STRM-BEHI-VH-HEIGH39.3490055000000001.0000000000000004.0000000000000000.9130402000000005.000000000000000



































































































































0.0000000000000000.00000000000000061739.000000000000000Very Low Low0.000000000000000C-STRM-BEHI-VL_L18.9890732000000002.0000000000000001.0000000000000000.0000000000000006.000000000000000
























1.6762651000000009.82318060000000061715.000000000000000Extreme0.164203000000000C-STRM-BEHI-EXTREAM27.4377665000000002.0000000000000001.0000000000000000.9622555000000005.000000000000000





0.6014940000000003.524850400000000151710.000000000000000Extreme0.164203000000000C-STRM-BEHI-EXTREAM3.9381958000000002.0000000000000001.0000000000000000.96225550000000011.000000000000000

















































6.23824380000000014.61328030000000061661.000000000000000High Very High0.250422100000000C-STRM-BEHI-HEIGH-VH66.9540289000000002.0000000000000002.0000000000000000.58662160000000015.000000000000000



















































16.41423170000000026.04903600000000061610.000000000000000High Very High0.575332400000000C-STRM-BEHI-HEIGH-VH76.6811785000000002.0000000000000004.0000000000000000.91304020000000018.000000000000000



























2.5715176000

a study of bank erosion rates within …a study of bank erosion rates within selected reaches of the...

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