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The Role of Wetlands during LowFrequency Flooding Events in the RedRiver BasinS.P. Simonovic & K.M. JulianoPublished online: 23 Jan 2013.

To cite this article: S.P. Simonovic & K.M. Juliano (2001) The Role of Wetlands during Low FrequencyFlooding Events in the Red River Basin , Canadian Water Resources Journal / Revue canadienne desressources hydriques, 26:3, 377-397, DOI: 10.4296/cwrj2603377

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The Role of Wetlands during Low Frequency Flooding Events

in the Red River Basin

Submitted February 2001; accepted May 2001Written comments on this paper will be accepted until March 2002

S.P. Simonovicl and K.M. Juliano2

ABSTRACT

Research studies have identified the functions and the numerous and wide rangingbenefits that wetlands offer to society. The role that wetlands play in 1ow frequencyflooding events, however, is one function for which further research is necessary.

Through the use of a case study this paper investigates the role of wetlands inlow frequency floods, using the Rat River watershed in southeastern Manitobaas a representative watershed of the Red River basin. This investigation was

accomplished through the use of the Hydrologic Engineering Centre's HydrologicModelling System (HEC-HMS). Three scenarios, with increasing wetland areas,

were run using data from1997, and comparisons were made. Based on the resultsof this case study it was found that a reduction in total flood volume could be

accomplished with an increase in wetland area. The results clearly show, however,that given a low frequency flooding event, this reduction in water volume is minimal,and that a reduction in the flood peak is non-existent.

RE5UME

Des dtudes ont fait ressortir les fonctions et les avantages nombreux et g6n6ra1is6s

que les milieux humides offrent i la soci6t6. Le r61e que jouent les mar6cages dans

les inondations de faible frdquence, cependant, est une fonction pour laquelle de

plus amples recherches s'avdrent ndcessaires. A I'aide d'une 6tude de cas, le pr6sentdocument examine le rdle que jouent les mardcages dans les inondations de faiblefr6quence, en se servant du bassin hydrographique de la rividre Rat dans le

sud-est du Manitoba en tant que bassin hydrographique reprdsentatif du bassinde la rividre Rouge. Cette 6tude a 6t6 men6e en faisant appel i un systdme de

mod6lisation hydrologique, soit le logiciei HtrC-HMS (Hydroiogic EngineeringCenter-Hydrologic Modelling System). Trois sc6narios comportant des zones

humides de dimensions oui allaient croissant ont 6td exdcutds i l'aide de donndes

l Professor, Department of Civil and Environmental Engineering, University ofWestern Ontario, London, ON

2 North/South Consultants Inc., Winnipeg, MB

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de 1997 et des comparaisons ont 6t6 6tab1ies. D'aprds 1es r6sultats de cette 6tude de

cas, on a constat6 qu'il est possible d'obtenir une r6duction du volume d'inondationtotal gr6.ce i l'accroissement des zones humides. Les r6sultats indiquent clairement,cependant, que dans 1e cas des inondations dc faible fr6quence, cette r6duction dans

le volume d'eau est minime et qu'i1 n'existe aucune rdduction dans le d6bit de pointede crue.

INTRODUCTION

Over the last few decades there has been a shift in the public perception of wetlandsand the role that they play in both rural and urban environments. Scientific studiesregarding the identification and functions ofwetlands have contributed to a greaterappreciation of their various roles. Some of the benefits with which wetlands have

been accredited include -rvater purification and the cycling of water recharge, habitatfor wi1d1ife, and recreational opportunities for individuals. These research studieshave identified the functions and the numerous and wide ranging benefits thatwetlands can offer society. The role that wetlands play in low frequency floodingevents, however, is one function for which further research is necessary.

The Prairie Provinces of Canada contain some of the richest agricultural landsin the world. Due to the high productivity of the soil, there has been a substantialincrease over the last century in demand for this fertile land. With increased

agricultural intensity many wetland areas have been converted to farmland (Adams,1988). By 1970 this had resulted in the conversion of 1.2 million hectares ofwetlandsto agricultural lands in the Prairie Provinces of Canada (Adams, 1988; Lynch-Stervart, 1983). According to the Sierra Club (1998), there has been a reduction of98%o in the number of wetlands in the Red River basin. The Sierra Club suggested

that increasing the number and size of wetlands could result in a decrease in waterlevels during spring runoff periods, and that conserving the remaining wetlandareas and restoring those that have been drained and filled would result in reducedflooding. There are many opinions regarding this issue.

Some individuals regard wetlands as storage reservoirs that can slow stormrunoff, but a wetland's response to such an event wouid no doubt depend on manyfactors including antecedent conditions. Wetlands have been shown to providemany valuable services including those listed above but the role that wetlands playin alleviating flood impacts has not been clear. The issue concerning the role ofwetlands in low frequency floods has become prevalent in the last few years due tothe flood experienced in the Red River Va11ey in 1997, which resulted in significanteconomic damage to both public and private property in Canada and the UnitedStates (International Red River Basin Task Force, 2000). The International JointCommission has investigated the role of wetlands in 1ow frequency floods througha set of comparative studies done in the USA (on the Maple and Wild Ricewatersheds) and Canada (on the Rat River watershed). A Canadian project (Julianoand Simonovic, 1999) addressed the limited question of the role of wetlands inreducing flood damages in the Red River basin.

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In this study a hydroiogic model was used to quantify the impacts of wetlandson low frequency flooding events. Models have different modelling capabilities. Some

components that models may incorporate are precipitation, snow accumulation and melt,evapotranspiration, interception, infiltration, surface drainage and runofl depressionstorage and routing, subsurface soil water flow and channel routing (HydrologicEngineering Centre, 1988). Given these many options, it is the task of the modeller todetermine which model meets the individual needs of the particular watershed. Thisdecision may also be affected by the availability ofdata, or other restrictions.

Hydrologic models can be classified as either lumped or distributed. In lumpedmodels a basin is considered to be homogeneous in terms of its spatial characteristics.That is, one location within a catchment is considered to have the same spatialcharacteristics, such as uniform rainfall, as another area in the catchment (Linsleyet a/., 1982). This type of model is often referred to as a 'black box'; results are

strictly determined by the input/output data (Singh 1988). In distributed models,however, one large catchment is divided into many smaller units, which are simulatedseparately and then combined to get a final catchment response. The advantage ofusing a distributed model is that the spatial variability of the watershed can be takeninto account. Given sufficient input data these models can yield better results thanlumped models.

For the purposes of this paper a wetland will be defined as an area of land"that is saturated with water long enough to promote wetland or aquatic processesas indicated by poorly drained soils, hydrophytic vegetation, and various kinds ofbiological activities which are adapted to a wet environment" (National WetlandsWorking Group, 1987). This Canadian definition is simple, yet it takes into accountthe essential features for which wetlands have become known.

This paper focuses on an investigation of only one of the functions of wetlands;their role in low frequency flooding events. In order to gain a ful1 understandingof this role the authors supply background information on hydrologic functions andsome history of flooding in the Red River Valley. A case study follows which givesdetails of the hydrologic model used, the data used in the model, and the resultsgenerated. We conclude with a discussion of the results and the conclusions drawnfrom the research.

WETLANDS

Wetland Hydrology

"Wetland hydrology is the single greatest impetus driving wetlands formation"(Tammi, 1994). Additionally, hydrologic conditions influence and determine manyof the characteristics of a wetland. The size of a wetland and the soecies foundwithin it, are both determined by its water status (Mitsch and Cosselink. 1993).Wetland soils and nutrients are also influenced by hydrologic conditions (Kadlec andKnight, 1996).

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Water enters and exits a wetland's system through a varrety of processes.

Surface runoff, groundwater discharge, precipitation, and streamflow are means

through which water enters a wetland. Alternatively, wetlands lose water throughgroundwater recharge, evapotranspiration and streamflow. Both the inflow and theoutflow from a wetland are variable. For example, inflow from surface runoffoccursafter a rainfall event, or during and after the spring me1t. Thus, inflow from a

rainfall event is dependent on the climate, which is unpredictable, while springmelting is seasonal. Outflow from evapotranspiration is dependent upon the sun and

is therefore on a diurnal cycle. The volume of water that a wetland stores is directlyrelated to the balance between these inflows and outflows, and the wetland basin

characteristics (Kadlec and Knight, 1996).Wetland areas commonly have fluctuating water levels depending on the

geomorphic setting, water source, and the hydrodynamics of the system itself(National Research Council, 1995). These factors interact with each other,contributing to the uniqueness of a specific wetland area. Both abiotic and bioticcharacteristics of a wetland are controlled by the hydrology of that wetland, and vice

versa (National Research Council, 1995).

Hydrologic Functions

Wetland functions can be divided into many different categories, but for simplicity,they are generally categortzed into three main groups: hydrologic functions, bio-geo-chemical functions, and habitat and food web functions (National Research

Council, 1995). These three functions are fundamentally linked to each another.

Within each of the broad categories, wetland functions are divided further into more

specific roles. Because wetland values are strongly linked to these specific functions,each function has one or more values associated with it. Some of the hydrologicfunctions associated with wetlands will be discussed.

The long-term storage of surface water, groundwater recharge (NationalResearch Council, 1995), and the discharge and recharge of streams located in close

proximity to a wetland area (Richardson, 1994) are all hydrologic functions thatwetlands have been accredited with. The reduction of downstream flood peaks due

to a wetland's short-term surface water storage capability has also been accredited

as one of their functions (National Research Council, 1995). The theory is thatwetlands temporarily store runoff water which reduces channel stage and channelvelocity. This results in floodwaters reaching the main channel at different times,which ultimately results in the protection of downstream communities. This couldbe of tremendous value to communities as it potentially reduces property damage

due to floodwaters. Whether this is true given the volume of spring runoff in the

Red River Valley during low frequency floods is further investigated in this paper.

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Wetland Decline

Wetlands have historically been thought of as 'unexploited wastelands' (Lynch- Stewart,1983). Although there are many functions of wetlands, society does not always affixa value to those functions. The value of a wetland will often depend on the dynamiceconomic circumstances at the time, its location, and what the wetland is perceived tobe providing (National Research Council, 1995). A wedand in one geographic locationmay offer the same benefits as one in another location, but if those particuiar benefits

are not recognized, or are not valued by society in that location, they are perceived to be

worthless. Wetland value in the oast has been focused on its ootential to be used for moreproductive purposes such as ugri..rltu.", urbanization and industrial development.

Of all the reasons for wetland decline, the pressures posed to increase landacreage for agricultural purposes has been the major force behind wetland drainage(Williams, 1990b). Additionally, government support programs encourage farmersto drain wetlands (Rubec et al. in van Koot, 1993). This perspective can also be seen

in the legal history of the prairie provinces; statutes and'common iaw'both ensuredthat the drainage of wetlands for agricultural production would require minimaleffort (Percy, 1993). Most of the wetland areas considered to be at risk are located onprivate land or are owned by provincial governments (Cox,7996). Over the years,increased consumer demand and increased cost of owning and operating agriculturalland has forced farmers to take full advantage ofall potential areas on their property.This has resulted in the use and drainage of marginal lands, including wetlands.Hanuta (7999) showed that wetlands may have composed 18%o of the land area in theRat River watershed before agricuitural development. Current land use data showthat wetlands now compose only 3% of the land area, a significant reduction.

Government Regulation

The Canadian Constitution clearly gives the provinces the majority of powerconcerningwetland conservation and depletion (Percy, 1993). The federal governmentmay use its authority and enact general rules over wetlands only if those wetlands are'linked to specific areas of federal jurisdiction under the Constitution'. This is due tothe fact that provinces not only own the natural resources within their boundaries, butprovinces also have jurisdictional power over property and civil rights.

Two pieces of federal legislation indirectly concern wetland s; the Migratory BirdsConvention Arl and the Fisheries Act (Percy, 1993). The Migratory Birds ConaentionActhas one direct reference to wetlands concerning the prohibition of polluting anywaters or surrounding land that migratory species might use. Percy states thatthe Act is not concerned so much with the orotection of habitat as it is with thephysical protection of the migratory birds. ihe Fisheries Act, on the other hand,is much more direct in terms of its reference to wetlands, although this section ofthe Act is rarely enforced (Percy, 1993). This Act prohibits any action that resultsin the harmful destruction, disruption or alteration of fish habitat. The federalgovernment, however, is reluctant to enforce these powers.

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Despite the fact that these two Acts of the federal government grant limitedpowers concerning wetlands, there are other federal programs and initiatives inplace which influence wetland depletion and conservation: Federal Wildlife Policy,

Federal Land Use Policy, Federal Policy on Wetland Conservation, the InternationalWetlands Convention, and the North American Waterfowl Management Plan.Although the federal government has effectively pursued the mandates of these

programs and policies, most of the federal action has been restricted to the form ofco-operative framework announcements (Percy, 1993).

It appears that most of the governmental influence on wetlands comes from theprovincial governments. In Manitoba, for example, the Water Rights Act deals withwetland drainage in one broad category which includes all types of water bodies

in the orovince. and the orovince holds the vested interest. The Act states thatthe diversion of any type of surface water without a license is prohibited (Percy,

1993). For example, in order for a landowner to drain a wetland on his property inthe Red River Valley, he must apply for a drainage license explaining the purpose.

Landowners, however, generally only submit applications where land drainage willbe substantial and thus, smaller operations are rarely penalized unless there is acomplaint. Thus, some wetland decline can be accounted for by the fact that areas

can often be drained without anyone being held accountable. It is therefore often tothe farmer's advantage, in terms of time and money, to do preciselythis.

The Government of Manitoba's Water Policy #6.6 states that "the Protectionofwetlands shall be a consideration in planning and developing drainage projects"(Province of Manitoba,1990). The government in 1990 adopted this amongother water policies. Policy #6.6's intent was to "protect important wetlands fromdestruction and land development". It was recognized that the majority of projects

that resulted in wetland loss occurred on privately owned agricultural land. Thisdocument also recognized that the prevention ofthe destruction ofwetlands cannotbe achieved through regulation alone but public education and incentives must also

be used.

Wetlands andThe Red RiverValley

As in the rest of Canada, the Red River Valley has undergone a decline in the

number of wetland areas. Permanent and temporary wetlands covered significantportions of the valley during the nineteenth century (Krenz and Leitch' 1993).

As settlements deveioped, well-drained land became scarce and resulted in settlers

turning toward poorly-drained soils for their livelihood.In the Red River Valley wetland decline is often associated with increased

spring runoff. This idea was reinforced during the spring of 7997 when theriver experienced unusually high water levels. Severe flooding, however, has been

occurring for many years, including those years prior to the surge of development inthe valley. "The flood of 7776 was of vast proportions and part of the oral traditionof the region" (Bumsted, 1997). Addrtionally, the flood of 1826 was the worst flood(for which records exist), far surpassing the severity of the flood of 7997.

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There are many opinions regarding the role of wetlands in flood controi. One

of the Sierra Club's suggested solutions to reducing the severity of the flooding in

the Red River Valley is wetland conservation and restoration (Sierra Club, 1998).

According to this organrzatron., the restoration of those wetlands that have been

drained, fi1led and destroyed "can help minimize peak river flows, and improve

the health of the river system" (Sierra Club, 1998). It suggested that "a program

which begins to acquire or manage drained wetlands would help minimize future

flooding". It is important to note, however that "very rarely has the importance

and value ofthese natural mitigation strategies been quantified, and techniques for

assessing the effectiveness and exact nature of their role have not been developed"

(Williams, 1990a).

CASE STUDY: THE ROLE OF WETLANDS IN THE RAT RIVER WATERSHED

The present case study investigates the role that wetlands play in flood control, but

the limitations of this research must be recognized. The results and conclusions

of the study are based on one low frequency flood year, 1997. The impacts ofwetlands are generalrzed for the entire Red River basin, based on the results from

the Rat River watershed. Extrapolating the effects of drainage on peak flows and

volumes to the entire basin is difficult as peak timing is a major consideration. The

availability of data also limits the choice of the modelling too1, in addition to the

sub-routines that could be used within the selected model. Although records show

that the Rat River experienced more extreme flooding conditions in other years'

7997 provided the most complete set of data.

The Study Site

The Rat River watershed with an area of approximately 1550 km2 is located

approximately 30 km southeast of Winnipeg and the river flows into the Red

dirr.r n"u. St. Agathe (Figure 1). Although one of the smaller watersheds withinthe Red River basin in terms of drainage area, the Rat River represents z typicalriver system in the Manitoba portion of the basin. Like other watersheds withinthe basin some of the areas are used for agricultural purposes, while others are

considered to be marginal and used for iivestock production. There still exists the

large Rat River Swamp which is bisected by the river. Due to local fires the peat

layer in this swamp has been reduced, but some peat is still present to various

depths. Similar to other watefsheds within the basin (such as the Pembina),

d,riitrg periods of high water levels, which occur during the spring, the Rat River

overflows its banks. In the Rat River, this results in the flow of water into JoubertCreek, which flows from east to west and lies just to the north of the Rat River.

It eventuaily joins the Rat River at Ste. Pierre-Jolys. Other small communities inthe watershed are St. Malo and Grunthal. These communities and small villages

and farms are scattered throughout the watershed, making a total popuiation of

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'*n, ".,r lr.Aqathe i,'*:."'-... t \ *--': t... \. stninbu.h t.,, r.,Steinbach '\

1 'r llt"'):_ 1 _ ,,I t| _rr.-.,i l1\r;;b;=i

if^.r,,

--*. I Gauge Station I I

Figure 1. The Rat River Watershed lllustrating the Two Flow Gauge Stations Used in This Study.

approximately 3,000. The western portion of the watershed, closest to the RedRiver, is almost exclusively cropland. The central part of the watershed is a mixof trees, grassland, and cropland, while the eastern portion is characterized byforest and wetland areas. There are several Provincial Trunk highways, provincialtwo-lane paved roads, and rail lines in the watershed.

HEC-HM5

The model selected for this study was HEC-HMS, developed by the U.S. ArmyCorps of Engineers (U.S. Army Corps of Engineers ,7998). HEC-HMS essentiallyreplaces HEC-1 and provides numerous options for simulating precipitation runoffprocesses, with the ability to perform continuous hydrograph simulations over longperiods of time. It accomplishes this through the use of a 'single-reservoir soil-moisture representation'. It also computes spatially distributed run-off values usinga grid ce1l'depiction of the watershed, but does not have the capability ro performcontinuous moisture accounting or snow accumulation and melt simulation.

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HEC-HMS contains three components: a basin model, a precipitation model,

and a control specification section. In the basin model, choices can be made

concerning loss methods, runoff transformation methods and routing methods. Inthis component the user can also select the use of a diversion. The precipitation

model allows for the incorporation of historical or hypothetical precipitation data.

Control specifications are used to specify the start and end time and date for a

simulation. This model has the option to allow for the basin runoff to be 'quasi-

distributed'. This can be accomplished through the use of the 'Modified Clark

method', superimposing grid cells on the basin where rainfall and losses are tracked

for each cell. HEC-HMS also provides the ability for parameter oPtimiz tion. The

modeller is able to impose constraints on Parameter values.

There were several reasons for selecting HEC-HMS. Although a distributed

model has the advantage of being more physically based than a lumped model, one

cannot take advantage of this quality if the data set for the watershed of interest is not

complete. As stated by Linsley et al. (1982) "unless the input rainfall and the catchment

characteristics are known with comparable detail, the solution may be no better ffor a

distributed model] than that of a lumped model". This is the case for the Rat River.

Although data have been collected for a number ofyears, they have not been collected

consistently at each station. For example, only one (of four) of the daily surface water

flow gauge stations was operational in the watershed during 1997.Distrlbuted models

are more complicated models and take into account more spatial variables than aiumped model such as HtrC-HMS. With this particularwatershed, there is not much

variability in land use; it is quite homogeneous. The assumption is that using HEC-HMS may be as good as using a distributed model with incomplete data.

In HEC-HMS there is not a component that specifically considers wetlands and

their interactions. Wetlands were therefore modelled using the 'diversion' option in

the program. A diversion operates by allowing a user-specified portion of the flow

to be diverted. It is important to note that a diversion reflects the storage capacity

of the wetland, but it does not reflect the location of the wetland. When the model

was calibrated, the diversion option was not used as wetlands were considered to be

an integral part of the watershed. From the land-use data, wetlands were determined

to comprise 3o/o (27.62 km2) of the area of interest and this is the value that was

considered to be present during calibration. For each ofthe three scenarios, allwaterfrom the watershed was considered to travel into the diversion (wetland) before it was

considered as runofT. In the first scenario, the land area considered to be wetland was

2o/o greater than that with which the model was calibrated; this resulted in a total

of 46.04 km2 (Table 1). In the second scenario, 5%o additional land was dedicated to

wetlands (73.66 km')) while in the third scenario, 10%o additional land was considered

to be wetland (119.70 km'?). In a report recently submitted to the International JointCommission concerning historical landscape reconstruction, wetland was one of the

land-use categories considered (Hanuta, 1999). This lePort used Dominion Land

Survey township maps from the 1870s and textual information from documents

and field notes to determine the pre-settlement landscape of the Red River Valley.

Comparing the area of interest in this report with Hanuta's findings, we found that

wetlands may have historically comprised about 180/o of the study area, slightly higher

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than any of the scenarios considered. This higher valueHanuta's classification of wetlands including marshes,weeds, is different from the definition used in this report.

may be due to the fact thatswamps, muskeg, hay and

Table 1. A comparison of total wetland areas for the three different scenarios.

Data Availobility and Description

Data were collected from a variety of sources. A1l data were provided free of chargeexcept for the climate data, purchased from Environment Canada. The hydrologicdata from Manitoba's Department of Natural Resources, Water Resources Branchincluded snow survey data, start melt dates in the spring, daily discharge data andairborne gamma snow cover data (Table 2).

Table 2. Summary of data available from Manitoba's Department of Natural Resources, Water

Resources Branch.

Data collected from Environment Canada included daily maximum temperature,daily minimum temperature, daily total rainfall, daily total snowfall, and dailytotal precipitation (Table 3). Land use data were provided by the Prairie FarmRehabilitiation Association in a Geographic Information Systems format. The datawere divided into seven classes: annual cropland, trees, water, grassland, wetlands,forage crops, and urban and transportation. The land use data showed the currentwetland area in the watershed tobe 3o/o of the entire area.

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Scenario Percent ofTotal Watershed Area Area (km'z)

27.6246.0473.66

719.7

Current1

2

3

3

5

81aIJ

Year # of Stations withSnow Survey Data

(snow depth and

water content)

Staft Melt

Dates

# ofStations # of Flight Paths

with Daily with Airborne Data

Surface Water

Flows

1950

r974t9797986t9961997

0

4A

40

4

\.2^ ^tcs

Yes

Yes\./^ ^I t5

Yes

Yes

1.

444z1

0

0

0

0AT

4

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Table 3. Summary of data available from Environment Canada.

Year Maximum Daily

Temperature

Minimum Daily

Temperature

Total

Rainfall

Total

5nowfall

Total

Precipitation

Solar

Radiation

1950

1974 Winnipeg

Jan-Dec

1979 Winnipeg

Jan-Dec

1986 Zhoda

Jan-Dec

ZhodtT- ^_T-\--

Zhoda.

Jan Dec

ZhodaT. -_T)^^

ZhodtT^ -_T'\-^

Winnipeg

Jan-Dec

1996

St. Pierre

Jan-Dec

/̂.noo1

Jan-Dec

Sr-P*t-Jan-Dec

-/,no.1l

Jan-Dec

St. Malo

Jan-Dec

;----=:--5t. t'rerre

Jan Dec

-Lnoda

Jan-Dec

St. MaloT^ -_T-\ -..

S,- Pr**Jan-Dec

St. Malo

Jan-Dec

bt. rrerre

Jan-Dec

---=,---._-LNOIA

T^ ^-T-r-^

Winnipeg

Jan-Dec

Zhoda

Jan-Dec

1997

St. Pierre

Jan Dec

1̂.non

Jan-Dec

St. PierreT^ -_Tt-^

Zh.d^

Jan-Dec

St. Malo

Jan-Dec

,..-5t. l'rerre

Jan-Dec

-Lnoda

Jan-Dec

St. MaloT^ -_n-^

St. Malo

Jan Dec

:----=:-5t. -t'rerre

Jan-Dec

/̂.oooa

Jan-Dec

Winnipeg

lm7-17May 29-Jun 1

Oct 3-Dec 31

St. Pierre

Jan-Dec

/̂.noo

Jan-Dec

Model Development

Data availability strongly restricted the model that could be used to investigate the

role of wetlands in flood control. The data also restricted the options that could be

used within the selected model. For example, due to data limitations concerningthe availability of flow stations, only 920.80 km2 of the total watershed (1550 km'?)

was considered. The areas that were not used in the modelling process include the

area downstream of the last gauge station (Otterburne) and the area upstream ofthe first gauge station (Sundown) (Figure 1). This second area was not considered

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because the flow was used as a boundary condition at Sundown. If the area hadbeen considered, precipitation data would have been used, and the flow data wouldnot have been used, as its use would have resulted in accounting for the same

factors twice; that is, fallen precipitation already included within the flow, would be

included a second time as precipitation. It was decided that flow data would give a

better representation of the conditions present in this area, and that this additionalarea of the watershed would therefore not be included in the modelling process. Theremaining watershed was divided into two basins, Joubert Basin (357.00 km2) andthe Rat Basin (563.80 km':). The basin schematic developed in HEC-HMS can

be seen in Figure 2. Therc is a dam and reservoir in St. Malo, developed by thePFRA in 1958 for use as a water supply reservoir for both domestic use and stockwatering. Since that time the area has also been developed into a Provincial Park forrecreational purposes. Because this dam and reservoir operate year-round at the fullsupply level, it was not given special attention within the model.

HEC-HMS offers a variety of loss methods including gridded SCS curvenumbers, initial/constant, and Green and Ampt. The program also offers several

runoff transformation methods: Clark, Snyder, SCS, and Kinematic Wave. Routingoptions include: Muskingum, Modified Puls, Kinematic Wave and Muskingum-Cunge methods. The loss and runoff transformation methods selected for thisproject were the SCS Curve number and method. This number was determinedfrom the land-use data and from soil information. The routing option selected was

Figure 2. Basin Schematic.

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Kinematic Wave. After calibration these numbers were modified slightly from theirestimated values. The selection of all of these methods was determined by theavailability of data. The options selected resulted in the least number of estimationson the part of the modeller. Ideally it would have been optimal to test and comparethe various methods and to determine the methods that would best suit thiswatershed but the availability of data did not allow such comparisons to be made.

The current version of HEC-HMS does not take into account precipitation inthe form of snow and it therefore does not consider snowmelt calculations. Because

the timing and volume of snowmelt play a significant role in runoff generationeach spring in the Red River Valley, a method was developed to estimate these

parameters. Snow depth and density data at a specific date are given by the WaterResources Branch of the Manitoba Deoartment of Conservation. It was assumed

that this value reoresented the total snow oack that had accumulated since the firstsnowfall in the fall of the previous year. Thir;r an important assumption as some

snow may have fallen and melted during the late fall before temperatures werecold enough to allow snow to accumulate. From that date forward snowfali events

were determined from Environment Canada data, and these events were added tothe total snow oack. The additional values were assumed to have the same waterdensity as the snow pack that had accumulated, as snowmelt did not begin for several

weeks after most of the new snow had fallen. Again, this is a large assumption.To determine the date and the rate

^t which the snow melted, temperature data

were used in conjunction with a mean temperature index. This index correlatesmean daily temperatures with daily snowmelt (Gray, 1973). Thus, a start meltdate was determined using this index and the snowmelt calculation was performedaccording to temperatures on specific days. It is important to note that althoughmany assumptions had to be made to account for snowmelt, it was deemed a

necessary procedure to ensure that snowmelt was included in the modelling process,

given this limitation of HEC-HMS.Only one flow station had data for 1997; as a result, flows were generated for

a second station. This was accomplished by investigating the relationship betweenthe two flow stations, Otterburne and Sundown, for 7996, and the daily percentdifference in flow was found. This relationship was established for 7997, resulting invalues for Sundown. An assumption was made when assigning these values to 1997;the relationshio between Otterburne and Sundown was considered to be consistentfrom year to year. This may not be the case and this assumption should be taken veryseriously and tested through sensitivity analysis.

ModelCalibration

The model was calibrated manuaily using the following parameters: SCS 1ag, andSCS curve numbers. The computed peak discharge and computed total dischargevolumes for 1997 were found to be 752.7 m3/s and 165.1 x 106 m3, respectively(Figure 3). The observed peak discharge and observed total discharge volume were173.0 m3ls and775.9 x 106 m3, respectively.

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Figure 3. 0bserved Versus Simulated Runoff Hydrograph for the Rat River Watershed.

ModelAnolysis

To determine the influence of wetlands on flood control, three different scenarios

were simulated. Filling the diversion prior to letting any of the water flow into the

sink resulted in a 'chipping' effect on the hydrograph. As the area of the wetlandincreased, the hydrograph's rising limb occurred over a shorter and shorter period oftime. Also, the hydrograph peak was not affected throughout any of these scenarios.

In the three scenarios it is assumed that water for the wetland is diverted justupstream ofthe final flow gauge.

A 2o/o increase in wetland area resulted in a total wetland within the watershed

of 46.04 km2. With this amount of wetland area, the start of spring flow occurredon April 79, rather than April 18; thus, it took just one day for the wetlands tofill to capacity (Figure 4). The peak of the hydrograph remained at approximately752 m3/s, on April 23,with a total wetland storage impact at 3.7 x 106 m3. In thisscenario, the increase in wetland area of 2o/o resulted in a 2.2o/o total flood volumereduction (Table 4).

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Figure 4. 1997 Hydrograph for the Rat River Watershed with an Additional 270 Wetland Area; The Total

Wetland Storage is 3.7 x 106 m3.

Note: Total flood volume reduction is the ratio between the wetland storage for thatscenario and the total discharge volume for that year.

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Table 4. Total flood volume reduction corresponding to each percent increase in wetland area.

Scenario Percent Increase

of Wetland Area

TotalWetland

Area (km'?)

Total Flood Volume

Reduction 1997 (%)

2.2

5.6

1,7.7

z

5

10

46.04

73.66

779.70

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Figure 5 represents a 50lo increase in wetland area (73.66 km'z). With this area ofwetland, the start flow date occurred on April 20 rather than April 18; it thus tookapproximately two days for the wetlands to reach storage capacity. The peak of thehydrograph remained at 752 m3 /s on April 23, and the total wetland storage impactwas found tobe9.2 x 106 m3. In this scenario the increas6 inwetland areaof 5o/o

resulted in a 5.60/o total flood volume reduction (Table 4).

Figure 5. 1997 Hydrograph for the Rat River Watershed with an Additional 5% Wetland Area; The Total

Wetland Storage is 9.2 x 106mr.

Figure 6 represents a 700/o increase in wetland area (119.704 km'?). With this areaof wetland, the start flow date was April 21, ruther than April 18; it thus tookapproximately three days for the wetlands to ieach storage capacity. The peak of thehydrograph again remain ed at 752 m3ls on Aprll 23, and the total wetland storageimpact was found to be 18.4 x 106 m3. In this scenario the increase in wetland areaof 100/o resulted in an11..1.0/o total flood volume reduction (Table 4).

It is important to put the benefits of the flood volume reduction, as seen in Table 4,

in perspective. Comparing the percent increase in wetiand area with the total floodvolume reduction for 1997, the results seem to be proportional. For examplq a2o/o

increase in wetland area is equivalent to approximately a 2o/o decrease in total floodvolume reduction. This relationshio can also be seen in the two other scenarios. Thisreduction in volume is not a reduclion in the peak of the hydrograph, and thereforenot a reduction in flood damages. Also, because of the diversion modelling, thesewetlands were located where the Rat River meets the Red River, zt area considered

prime agricultural land. Thus, although these percent increases in wetland areas couldresult in reduced flooding, it also would result in decreased agricultural production.

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Figure 6. 1997 Hydrograph for the Rat River Watershed with an Additional 10%o Wetland Area; the

Total Wetland Storage is 18.4 x 105 m3.

One option raised during the public hearings conducted by the International JointCommission after the release of its final report (http://www.ijc.org) was that moreattention be given to the introduction of control structures in the Red River Valley. Itis important to acknowledge that this option is going beyond the role that wetlandscan play during the low frequency floods and represents development of additionalstorage in the basin. This could result in a shift of the impact from the base of thehydrograph to the peak (Figure 7). This would be accomplished through the use of a

gated control structure, where water is diverted into the structure after a specific flow has

been reached. In Figure T,water was diverted when it was flowing at approximately 100

m3ls. This is not an example of wetland restoration but of what could occur given thedevelopment ofstorage control structures located close to the river.

To determine if wetland restoration is a cost-effective method of reducingflood impacts, a benefit-cost analysis should be performed. The Sierra Club has

recommended that a cost-effective approach be used to reduce flooding in the basin;thus despite the fact that it has been established that there are no (flood-related)benefits associated with the proposed alternatives, this paper includes a brief lookat the cost of increasing wetland areas. In this type of analysis, the benefits andcosts are individually determined and compared. This allows decision-makers tomake choices based on quantitative data. Because the data necessary to performa comprehensive benefit-cost analysis were not available, only the total cost ofrestoring wetlands was considered. The values used in this report are based uponthose values determined by Leitch et a/. (1999) in their report, Draft Report: Effectof Wetlands on Flooding. A cost of $a5 (U.S. dollars) per acre-foot of storage peryear

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was used to determine totalwetland costs for each of the three scenarios (Table 5).

This value is the average total cost determined for simple restoration (1 foot bounce),

per acre-foot of restoring wetlands within the Maple and Wild Rice watersheds in the

United States. This restoration cost is the tatal cost of restoring wetlands for water

storage purposes on1y, not the cost for restoring wetlands for ecological purposes.

Figure 7. 1997 Hydrograph for the Rat River Watershed with an Additional 5% Storage Atea, Using a

Storage Control Structure.

Table 5. Total cost ofwetland restoration per year for ea(h ofthe three scenarios given a cost of 545

(US S) for each acre-foot of storage per year, for 1997.

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Scenario Percent Increase

of Wetland

Area

Additional

Wetland Area

(km')

18.42

46.04

92.08

Total Flood Volume

Reduction

1997 (o/o)

2.2

5.6

11.1

Acre-Feet

of Storage

Total Cost

of Wetland

Restoration

per Year (U5 5)

1.34,424

336,058

672,777

1,

2

3

2

5

10

2,987.79

7,467.96

14 g?5 gl

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In the first scenario, the addition of 18.42 km2 of wetland area (wetland area inaddition to that which currently exists) resulted in a total restoration cost of ffL34,424

per year. The total flood volume reduction associated with this cost was 2.2o/o. Forthe second scenario, the addition of 46.04 km2 resulted in a totai restoration cost of$336,058 per year while an addition of 92.08 km2 resulted in a cost of ff672,177 per

year. The total flood volume reductions associated with these scenarios zre 5.60/o and1L.10/o, respectively. It seems that these values are quite high given the modest totalflood volume reductions determined through the modelling process.

CONCLUSIONS

Based on the results of this study, a reduction in total flood volume can be

accomplished with an increase in wetland area. The results clearly shoq however,

that given a 1ow frequency high magnitude flooding event, the reduction in watervolume is minimal in comparison to the amount of land to be restored. This is

strongly supported for the Rat River watershed and can be seen in Figures 4, 5 and6. More importantly, the simulated increase in wetlands did not affect peak waterflows, and would therefore have a minimal impact in reducing property damages.

The results seen are for the Rat River watershed. Increasing wetlands by the

percentages indicated in this report would likely not have any effect on the total floodvolumes of the Red River during a 1ow frequency flood. That is, given the highestpercent increase in wetland area, and its corresponding total volume reduction, the

decrease in damages experienced would be very modest if extrapolated to the entireRed River basin. If wetlands were increased by 100/o in all watersheds in the valley,

a decrease in total flood volume of 1,L.1,o/o during a low frequency flood event still is

not significant. One must be careful when considering this as not all wetlands may

yield such a high total flood volume reduction since temperature and climate are

not uniform in the valley, and an 11.170 reduction may not be seen elsewhere. It is

also important to recall that the largest flood in the history of the Red River Valleyoccurred in7826, prior to basin development and prior to any drainage activities.

These results are limited by several factors: data strongly limited the model and

the sub-routines within the mode1. The conclusions are also based on data from onlyone large flood in L997. As well, the results from this study generalize the impacts ofwetlands on flood control for the entire Red River basin based on only one watershed

within it. It is crucial that the factors listed here be fully considered when reviewingthe results in Table 4.

ACKNOWLEDGEMENTS

The authors would like to thank the InternationalJoint Commission for funding themain portion of this research. Additional gratitude is given to Mr. Sajjad Ahmad, a

Ph.D. student at the University of Manitoba, for his assistance with the hydrologicalmodelling portion of this research.

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Bumsted, J.M. 1997. Floods of the Centuries: a History of FloodDisasters in the RedRiver Valley 1776-1997. Great Plains Publications, Winnipeg, MN.

Cox, Kenneth. 1996. Wetlands: An Integral Element of the Ecosltstezl. WorkshopSummary. Oak Hammock Marsh.

Gray, D.M. 1973. Handbook on the Principles ofHydrology. National Research Councilof Canada.

Hanuta, I. 1999. A Landscape Reconstruction using Dominion Land Survey TounshipMap; Areport prepared for the InternationalJoint Commission, http://www.ijc.org.

Hydrologic Engineering Centre. 1988. Comparison af Modelling Tbchniques forWetlandAreas. Project Report No. 88-4. Prepared for St. Paul District, U.S. ArmyCorps of Engineers.

International Red River Basin Task Force. 2000. The Mxt Flood. Getting Prepared,FinalReport to the InternationalJoint Commission, Ottawa, Washington, http://www.ijc.org.

Juliano, K. and S.P. Simonovic. 1999. The Impact of Wetlands on Fload Control in the RedRioer Valley af Manitaba. A report prepared for the International Joint Commission,Natural Resources Institute, University of Manitoba, Winnipeg, http://www.ijc.org.

Kadlec, R.H. and R.L. Knight. 1996.7ieatment Wtlands. Florida: CRC Press LLC.

Krenz, Gene and Jay Leitch. 7993. A River Runs North, Managing an InternatianalRiver Red River Water Resources Council.

Leitch, J.A., S. Shultz, G. Padmanahban and M. Bengston.1999. Draft: The Ro/e

of Wetlands in Flooding: Case Studies of truo Subtuatershed in the Red Rioer of the NarthBasin. North Dakota State Univerisity.

Linsley, Ray L., Max A. Kohler and Joseph L.H. Paulhus. 1982. HydrologltforEngineers. MrGraw-Hill Book Company, Toronto.

Lynch-Stewart, Pauline. 1983.Revietn and Bibliagraphy LandsCanada, Ottawa, ON.

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Reimold, RJ. 1994. WetlanrJ Functians and Values.In: Applied Wetlands Science and

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Richardson, CJ. 1994. "Ecological Functions and Human Values in Wetlands: AFramework for Assessing Forestry Impacts." Wetlands, 14 (1): 1-9.

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