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NRBS - Home Table of Contents		Northern River Basins Study Final Report 3.0 Major Findings 3.5 Flow Regulation Introduction Effects on the Peace River Effects on the Peace-Athabasca Delta Effects on the Slave River Delta Modelling Floods Relevant Documents Related NRBS Question: 10.   How does and how could river flow regulation impact the aquatic ecosystem? Introduction Flow regulation refers to the control of natural water flow to serve some human purpose, usually by withdrawing, diverting or storing it. If combined, the total flow of all diverted water in the country would form Canada's third largest river, smaller only than the St. Lawrence and Mackenzie Rivers. Most of these diversions were created to serve hydroelectric production. With hydroelectric dams, there are two sources of change that affect aquatic ecology: the impoundment of water in a reservoir upstream of the dam, and the control of downstream water flows. These simple alterations can affect many physical, chemical and biological aspects of the environment, including water flow patterns, ice formation, sediment transport, water chemistry, aquatic communities and habitat.
NRBS - Home Table of Contents Top of Page		The Peace River has experienced large-scale flow regulation since construction of the W.A.C. Bennett Dam in British Columbia and operation of the Gordon M. Shrum hydroelectric facility. Filling of its associated reservoir—Williston Lake—occurred between 1968 and 1972, resulting in the storage of nearly 41 trillion litres of water. The NRBS Hydrology Component initiated a variety of studies to better understand the physical, chemical and biological impacts of flow regulation on the basins environment. Challenged by the lack of comprehensive information on this topic, the NRBS studies focussed primarily on the effect of the Bennett Dam on hydrologic regimes and downstream regions within the Study area. This included the development of computer models to help predict the future consequences of flow regulation in the northern rivers. It also involved close collaboration with researchers performing similar investigations within the Peace-Athabasca Delta Technical Studies group. A more in-depth discussion of flow regulation impacts on the northern rivers can be found in the NRBS synthesis report cited at the end of this section. Effects on the Peace River
NRBS - Home Table of Contents Top of Page		Figure 3.5.1 Pre- and Post-regulation Mean Annual Peak Flows at Selected Sites on the Peace and Slave Rivers Figure 3.5.2 Pre- and Post-regulation Mean Monthly Flows at Selected Sites on the Peace and Slave Rivers NRBS scientists have confirmed that flow regulation on the Peace River has greatly altered several river characteristics, including seasonal flow patterns, ice cover formation and sediment transport. These, in turn, affect other physical characteristics of the river, including the quality and availability of certain habitat types. Flow Patterns Prior to regulation, the Peace River displayed seasonal flow patterns similar to other northern rivers dominated by snowmelt runoff—high flows in the spring and summer, and low in late fall and winter. The Bennett Dam has affected this pattern. While the annual amount of water flowing out of the dam is the same as before regulation, the timing of these flows has been altered. The dam releases significantly greater amounts of water during the cold months to meet rising power demands, and tends to store more water in the summer to refill the reservoir.
NRBS - Home Table of Contents Top of Page		One of the effects of flow regulation is to reduce mean annual peak flows (Figure 3.5.1). Immediately downstream at Hudson's Hope, peak flows are only 30 per cent of those recorded prior to regulation by the dam. These effects generally diminish downstream due to the influx of natural tributary flows. Due to the large inflow of water from the Smoky River, for instance, average peak flows at the town of Peace River remain at 71 per cent of historical levels. At Peace Point above the Peace-Athabasca Delta, peak flows are 63 per cent of historically recorded levels. Further downstream at Fort Fitzgerald on the Slave River, the influence of the unregulated Athabasca River boosts flows back up to 85 per cent. Flow regulation has altered the timing of seasonal high and low flows at locations immediately downstream of the dam. Under current conditions near Hudson's Hope, average seasonal low flows occur in June instead of March and average high flows occur in December instead of June (Figure 3.5.2). Prior to regulation, summer flows near Hudson's Hope were roughly twice that of winter flows. Following regulation, these summer flows have been cut in half and winter flows are four times greater. In fact, summer flows at Hudson's Hope are currently lower than the regulated winter flows (Figure 3.5.2). The situation is less pronounced further downstream. At Peace Point, summer flows are 66 per cent of historic levels, while winter flows are at 250 per cent. In light of the higher winter flows on the Peace River since regulation, the relative importance of tributaries to the overall flow volume is greatly reduced during this period. Prior to regulation, tributaries would double the winter flow between Hudson's Hope and Peace Point. The same volume of tributary flow now accounts for only 20 per cent of the winter flow at Peace Point. In contrast, tributaries now have an added significance during the summer months. It should be noted, however, that tributary flows have been relatively less in recent years, which appears to be tied to regional climate conditions. Sediment Transport and River Morphology Most sediments in the Peace River arise from its tributaries downstream of the dam, in particular the Smoky River. Consequently, Williston Lake does not have a large influence on the amount of sediments that flow into the river. However, lower peak flows have reduced the ability of the river to scour away the annual build up of sediments. As sand and silt accumulate in certain sections, the Peace River is slowly evolving into a new shape, resulting in changes to vegetation and wildlife habitat.
NRBS - Home Table of Contents Top of Page		The specific changes along each reach of the river depend upon the physical characteristics at each location. Many sections of the river are becoming narrower as sediment accumulates along the shoreline. Islands and sand bars are growing in some regions. Semi-aquatic plants and shoreline vegetation are beginning to colonize these new areas. Many of the small side channels and backwater snyes have been blocked off by silt and are slowly drying out. One of the most noticeable areas of change is the floodplain—the lowland area adjacent to the river that was periodically inundated with water. In the absence of high floods, the flood plain is drying out and being colonized by terrestrial vegetation and wildlife, such as trees and shrubs. The changes caused by flow regulation are very slow. Several decades will pass until the physical transformation of the Peace River is finished, and it will take centuries until all changes in wildlife and vegetation are complete. However, changes can already be seen along the Peace River. [Photo 8-05 on CD1: As a result of flow regulation, silt is accumulating along the banks of many sections of the Peace River and vegetation is beginning to grow along the shoreline, seen here upstream of Montagneuse Islands.] Ice Formation Ice formation affects many natural processes in a river system, including the type and availability of habitat, dissolved oxygen levels and flow patterns to name a few. Since the Peace River is normally covered with ice for almost half the year, changes to the ice regime caused by flow regulation can have profound ecological effects. The release of relatively warm water from Williston Lake during the winter months has significantly delayed and shortened the period of ice cover in reaches upstream of Fort Vermilion. Upstream of the British Columbia border, ice cover is the exception rather than the rule. Intermittent winter ice cover forms as far downstream as the town of Peace River. The dam does not seem to have significantly altered the timing and duration of ice cover in the downstream extremities of the Peace River.
NRBS - Home Table of Contents Top of Page		In select reaches of the Peace River, physical changes in the ice cover have also been observed. These changes are a result of a combination of factors that together alter ice cover formation in some areas. In river systems, ice cover usually begins as a number of flat "pans" that float on the water surface. In many reaches, these pans gently butt against one another and eventually cover the entire surface with a flat layer of ice (i.e., juxtaposed ice cover). [Photos 2 and 3 on CD1: Juxtaposed and consolidated ice cover] Under higher flows and steeper gradients, the force of the water can cause these pans to collide and be pushed under one another, leading to a thicker, rougher ice cover (i.e., consolidated ice cover). Higher winter flows from Williston Lake have caused this thicker, rougher ice to form in steeper reaches characteristic of the upper and middle portions of the Peace River. Some areas experience higher freeze-up and water levels that may cause surcharging of aquifers. In the town of Peace River, for instance, elevated groundwater levels have been known to flood the basements of some residences. Habitat The assessment of flow regulation effects on habitat was for the most part beyond the scope of NRBS research. A comprehensive assessment would require detailed inventories of habitat and wildlife, including information regarding the preferential use of habitat by wildlife. To understand the cause and effect relationships and to forecast changes into the future would require modelling efforts that are beyond the scope of the Study. Researchers did undertake to provide an assessment of flow regulation effects on river channel habitat by considering factors such as changes in channel geomorphology, riparian habitat and associated vegetation in representative areas along the Peace River. The effects of flow regulation on the deltas were reported in studies initiated prior to the NRBS and are being considered within the Peace-Athabasca Delta Technical Studies. In the absence of detailed information, researchers speculated about how flow regulation is affecting the availability of certain habitat types within the basin, and how this may affect the distribution of fish and wildlife populations.
NRBS - Home Table of Contents Top of Page		Lack of ice cover in the upper reaches of the Peace River encourages animals that require open water (e.g., beaver) and may provide additional winter habitat for fish. The increase in temperature, however, may induce the eggs of fall-spawning fish to hatch prematurely and could affect their survival. Where ice cover forms, nearshore zones may be clogged by frazil ice—the slushy mush of ice spikelets formed by freezing in turbulent waters. Frazil ice may affect the availability and quality of nearshore winter habitat for fish. The formation of thicker, rougher ice also has implications for the aquatic ecosystem. Open water sections, such as those associated with the Vermilion Chutes rapids near Fort Vermilion, are often important feeding and overwintering zones for fish. Higher winter flows resulting in thicker, rougher ice could reduce valuable fish habitat. In addition, higher water and freeze-up levels may eliminate the fish migration barrier posed by these rapids during the winter. Changes to the shape of the river can have both positive and negative effects on fish habitat, depending upon the location. Notably, the loss of side channels in many regions represents a sizeable loss in valuable fish habitat. At the same time, the drying out of isolated wetland areas will discourage populations of waterfowl, shorebirds, amphibians and other semi-aquatic species. Along the Peace River mainstem, the most sensitive area for this to occur is in Wood Buffalo National Park. In the short-term, growth of vegetation into the old floodplain and on islands within the river benefits a wide variety of species that like tall shrubs or forest habitat, including many species of mammals (e.g., moose and deer) and birds (e.g., yellow warbler, tree swallow and woodpecker). Effects on the Peace-Athabasca Delta
NRBS - Home Table of Contents Top of Page		As previously discussed, the effects of the Bennett Dam on water flows tends to decrease with distance from the dam. However, the ecological effects of the dam are perhaps most noticeable at the far end of the Peace River in the Peace-Athabasca Delta. NRBS work related to the delta was coordinated with the Peace-Athabasca Delta Technical Studies. Lakes and Channels It is long established that the decrease in summer flows due to regulation have reduced water levels in the lakes and channels of the Peace-Athabasca Delta. Efforts to combat falling water levels include the construction of several weirs along the channels that drain the delta: one on the west arm of the Quatre Fourches River (now removed), one on the Rivière des Rochers and another on Revillon Coupé. (Photo: 027 on CD1:) Researchers used a one-dimensional hydraulic flow model to evaluate the effects of flow regulation and the remedial delta weirs on water levels within the main channel systems of the delta. The model revealed that the weirs have successfully restored mean-annual water levels on many delta lakes and channels to conditions that existed prior to the construction of the Bennett Dam. At the same time, however, the weirs have reduced the natural seasonal fluctuations in water levels. This is an ecological concern, since these fluctuations help to maintain the delta's unique near-shore habitat and waterfowl staging zones. Furthermore, the weirs are not able to restore water levels in the delta's perched or isolated basins. Perched Basins During the period when Williston Lake was filled, the shoreline along the delta's perched basins was reduced by 36 per cent and the total water area declined by 38 per cent. This exposed roughly 500 km2 of mudflats, and marked the beginning of ecological change in the basins. In particular, productive sedge meadow habitat is slowly being replaced by woody vegetation, such as willow and poplar. Further information regarding ecological changes occurring in the delta and their impact on local communities is found in Section  3.4 of this report.
NRBS - Home Table of Contents Top of Page		Ecological changes have continued since the filling of the reservoir, due in large part to the disruption of ice and flood patterns. Water levels in the basins are replenished only through overland floods. The floods occurred approximately every second year during the 1960s prior to regulation, but only three times since. Historical records reveal that major flood peaks were produced during ice break-up in the spring. During this time, large volumes of water would back up behind ice jams on the lower Peace River until the river overflowed its banks. The deluge of water was enough to refill the perched basins and scour out stream channels. The major factors influencing the severity of the ice jams are higher water levels at the time of ice cover formation and relatively smaller tributary flows. As previously mentioned, higher winter flows result in a higher freeze-up elevation along portions of the river. This allows a greater volume of water to flow underneath without breaking the ice, and a greater amount of water is required to stimulate a jam. Furthermore, the floods were associated with high amounts of runoff from tributaries, especially the Smoky River. A preliminary study reveals that the amount of spring runoff from tributaries has been low in recent years. More water is now required to stimulate an ice jam, but less is available. Given these conditions, the release of water from Williston Lake required to produce these ice jams on a regular basis would be enormous and would have implications for residents immediately downstream of the dam. The dam's economic losses would also be large. Therefore, relying solely on the dam to stimulate ice jams is not a desirable alternative. Several management operations exist:
NRBS - Home Table of Contents Top of Page		Construct variable-height weirs to retain water in lakes and channels: Adjustable control structures could be constructed that would permit the entry of water into individual basins and prohibit drainage when water levels in the main channels and lakes decline. Some success has been had using similar weirs in the past, but funding and ownership / responsibility of these structures poses difficulties that must be resolved. Furthermore, this technique would only succeed in basins that receive water during some part of the year. Utilize hydraulic pumps to flood the perched basins: Hydraulic pumps are a cost-effective option to adjustable weirs. They could also be used in small-scale efforts to flood the perched basins that are not part of the main flow network. Create an artificial ice dam at a critical point in the delta: The Peace-Athabasca Delta Technical Studies group has already developed techniques to create artificial ice dams that could be used to backup water during the spring runoff period and achieve mid-scale flooding of the delta landscape. The success of this technique hinges on the timing and magnitude of winter flows, which in turn relies upon climatological conditions and winter flows through the Bennett Dam. From a hydrological standpoint, the best area to create such a dam is found in the Quatre Fourches channel at the site of the old rock weir, but this would not flood perched basins located in the delta's northern regions. A gated structure could be used in lieu of the dam to allow for fish migration. Create an ice dam on the mainstem Peace or Slave Rivers: The only management technique that could ensure large-scale flooding of the delta and its perched basins is to backup spring runoff behind an artificial ice dam on the Peace or Slave Rivers. However, the efficacy of an ice dam would again be dictated by climate and flows through the Bennett Dam. Further investigations are required to test the efficacy and ramifications of these options. In addition, the latter two options require negotiations with B.C. Hydro to modify winter releases from the Bennett Dam.
NRBS - Home Table of Contents Top of Page		Significant difficulty and expense could be avoided if the dam were to extend its high release period during years of high tributary flow. The combination of high tributary and headwater flow would increase the likelihood of ice jam-related floods in certain years without an excessive release of water from the dam. To assist in this effort, it would be useful to have a greater understanding of the processes dictating the level of tributary flows. Lower tributary flows are commonly associated with smaller winter snowpacks, an effect that might be attributed to climate variability. Habitat According to interviews conducted within the Traditional Knowledge Component, the loss of wetland habitat within the Peace-Athabasca Delta has had a profound effect on the ecosystem (Section 3.4). According to traditional residents of the delta, wetland meadows and marshy areas continue to be replaced by drier terrestrial plants. This has coincided with a marked reduction of semi-aquatic animals and waterfowl. In contrast, the increasing abundance of willow has provided improved conditions for moose. Effects on the Slave River Delta The Slave River Delta is more than 1,500 km downstream from the Bennett Dam, yet NRBS researchers have detected a few effects that may be attributed to flow regulation. Similar to the Peace River, the Slave River Delta now experiences lower peak flows. This has reduced the amount of sediment that is delivered to the delta. As one might expect, these changes are greatly diminished due to the distance from the dam and the influence of other water bodies, notably the Athabasca River and the Peace-Athabasca Delta. The Slave River Delta is a constantly evolving natural phenomenon. As the delta slowly grows into Great Slave Lake, the physical and ecological features of the region exist in a state of constant change. This natural process is very complex and, as a result, it is difficult to distinguish flow regulation effects from natural phenomena. The full impacts of flow regulation on the Slave River Delta are poorly understood and further studies are required to understand the changing dynamics of the Slave River Delta in response to flow regulation.
NRBS - Home Table of Contents Top of Page		Modelling Floods Researchers from the Hydrology Component developed a flood routing model that will help to demonstrate the impacts of regulation on the flow regime of the Peace and Slave Rivers. The new hydraulic model is more versatile than currently available hydrologic routing models, and provides details on water levels, velocities and discharges occurring at any point along the Peace River as a function of time. The model will be used to determine the effects of flow regulation on river channel and delta morphology, nearshore vegetation and aquatic habitat. The performance of the model has yet to be fully tested. So far, the model has worked well in predicting flow patterns for moderate flood events, such as that which occurred in 1987. Since flooding of the Peace-Athabasca and Slave deltas is related to ice-jam releases, a long-term goal will be to predict the impact of flow regulation on the ice regime. Relevant Documents NRBS Synthesis Reports Prowse, T. and M. Conly. 1996. Impacts of Flow Regulation on the Aquatic Ecosystem of the Peace and Slave Rivers. Northern River Basins Study Synthesis Report No. 1. NRBS Technical Reports
NRBS - Home Table of Contents Top of Page		Aitken, B. and R. Sapach. 1994. Hydraulic Modelling of the Peace-Athabasca Delta Under Modified and Natural Flow Conditions. Northern River Basins Study Technical Report No. 43. Andres, D.D. 1996. The Effects of Flow Regulation on Freeze-Up Regime, Peace River, Taylor to the Slave River. Northern River Basins Study Technical Report No. 122. English, M.C., Hill, B., Wolfe, P.M., Stone, M.A. and R. Ormson.  1996. Assessment of Impacts on the Slave River Delta of Peace River Impoundment at Hudson Hope. Northern River Basins Study Technical Report No. 85. Environment Canada. 1996. Peace / Slave River Cross Sections. Northern River Basins Study Technical Report No. 121. Hicks, F.E., Yasmin, N. and X. Chen. 1995. A Hydraulic Flood Routing Model of the Peace River, Hudson Hope to Peace Point. Northern River Basins Study Technical Report No. 76. Hicks, F.E. and K. McKay. 1996. Hydraulic Flood Routing Model of the Peace and Slave Rivers, Hudson Hope to Peace Point. Northern River Basins Study Technical Report No. 77. Krishnappan, B.G. and R. Stephens. 1995. Critical Shear Stresses for Erosion and Deposition of Fine Suspended Sediment from the Athabasca River. Northern River Basins Study Technical Report No. 85. Krishnappan, B.G., Stephens, R., Kraft, J.A. and B.H. Moore.  1995. Size Distribution and Transport of Suspended Particles, Athabasca River, February and September, 1993. Northern River Basins Study Technical Report No. 51.
NRBS - Home Table of Contents Top of Page		Northwest Hydraulic Consultants Ltd. and the Alberta Research Council. 1994. Winter Under-Ice Tracer Dye Studies, Travel Time and Mixing Characteristics, Peace River, Shaftesbury Ferry to Notikewin River, February and March 1993. Northern River Basins Study Technical Report No. 36. Prowse, T., Conly, M. and V. Lalonde. 1996. Hydrometeorlogical Conditions for Controlling Ice-Jam Floods, Peace River Near the Peace-Athabasca Delta. Northern River Basins Study Technical Report No. 103. Van Der Vinne, G. and D. Andres. 1993. Winter Low Flow Tracer Dye Studies, Athabasca River, Athabasca to Bitumont, February and March 1992, Part 1: Time of Travel. Northern River Basins Study Technical Report No. 7. Van Der Vinne, G. 1993. Winter Low Flow Tracer Dye Studies, Athabasca River, Athabasca to Bitumont, February and March 1992, Part II: Mixing Characteristics. Northern River Basins Study Technical Report No. 14. Walder, G.L. 1996. Proceedings of the Northern River Basins Study Instream Flow Needs Workshop. Northern River Basins Study Technical Report No. 66. Watson, L. 1996. Bibliographic Database of Hydrology / Hydraulics Sediment Studies on the Peace River. Northern River Basins Study Technical Report No. 111. Other Relevant Documents Prowse, T.D. and M.N. Demuth. 1996. Using Ice to Flood the Peace-Athabasca Delta, Canada. Regulated Rivers (in press). Prowse, T.D. and V. Lalonde. 1996. Open-Water and Ice-Jam Flooding Of A Northern Delta. Nordic Hydrology, 27 (1/2): (in press). Prowse, T.D., Aitken, B., Demuth, M.N. and M. Peterson. 1996. Strategies for Restoring Spring Flooding to a Drying Northern Delta. Regulated Rivers, 12: (in press). Wilson, E. 1995. Artificial Ice Dam 1994-1995 Field Report. Peace Athabasca Delta Technical Studies. September 1995. 12 pp + appendices.

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