Streamflow Regulation Research Articles

Influences of forests on water flows from headwater watersheds in Taiwan

Forests cover 59% of Taiwan island where disastrous floods, landslides and debris flows occur often due to heavy typhoon-season rainstorms, steep terrain, fragile geologic formations and frequent earthquakes. This study evaluated the hydrologic influences of forests on Taiwan’s headwaters watersheds and supports the century-old policy of designating protection forests for streamflow regulation and soil conservation. Despite rainfall intensity that often exceeds 100 mm/h overland flow rarely occurs on Taiwan’s permeable forest soils. High evapotranspiration totaling 800–1200 mm annually contributes to reduced streamflows. In Taiwan forests reduce stream sedimentation from landslides by enhancing slope stability with roots and protect water quality by minimizing stream temperature fluctuation, regulating nutrient concentration and filtering contaminants. Floods in Taiwan are mainly caused by heavy rainstorms exceeding 250 mm and are not significantly affected by the currently low level of annual forest removal. Rapid urbanization of some forested watersheds may cause increased peak flows and decreased low flows due to significantly reduced soil infiltration capacities. Forests’ influences are minimal on landslides, debris flows or floods caused by extreme natural events such as the 7.3 Richter-scale earthquake in September 1999 or the rainstorms exceeding 1000 mm during Typhoon Herb in August 1996.

Streamflow regulation and multi-level flood plain formation: channel narrowing on the aggrading Green River in the eastern Uinta Mountains, Colorado and Utah

The style and degree of channel narrowing in aggrading reaches downstream from large dams is dependent upon the dominant geomorphic processes of the affected river, the magnitude of streamflow regulation, and the post-dam sediment transport regime. We measured different magnitudes of channel adjustment on the Green River downstream from Flaming Gorge Dam, UT, USA, that are related to these three factors. Bankfull channel width decreased by an average of about 20% in the study area. In reaches with abundant debris fans and eddy deposited sand bars, the amount of channel narrowing was proportional to the decrease in specific stream power. The fan–eddy-dominated reach with the greatest decrease in stream power narrowed by 22% while the reach with the least decrease in stream power narrowed by 11%. In reaches with the same magnitude of peak flow reduction, meandering reaches narrowed by 15% to 22% and fan–eddy-dominated reaches narrowed by 11% to 12%. Specific stream power was not significantly affected by flow regulation in the meandering reaches. In the diverse array of reach characteristics and deposit types found in the study area, all pre- and post-dam deposits are part of a suite of topographic surfaces that includes a terrace that was inundated by rare pre-dam floods, an intermediate bench that was inundated by rare post-dam floods, and a post-dam floodplain that was inundated by the post-dam mean annual flood. Analysis of historical photographs and tree-ring dating of Tamarix sp. shows that the intermediate bench and post-dam floodplain are post-dam landforms in each reach type. Although these two surfaces occur at different levels, they are forming simultaneously during flows of different magnitude. And while the relative elevation and sedimentologic characteristics of the deposits differ between meandering reaches and reaches with abundant debris fans and eddies, both reach types contain deposits at all of these topographic levels. The process of channel narrowing varied between fan–eddy-dominated and meandering reaches. In the meandering reaches, where stream power has not changed, narrowing was accomplished by essentially the same depositional processes that operated prior to regulation. In fan–eddy-dominated reaches, where significant reductions in stream power have occurred, channel narrowing has been accompanied by a change in dominant depositional processes. Mid-channel sand deposits are aggrading on deposits that, in the pre-dam era, were active gravel bars. These deposits are creating new islands and decreasing the presence of open-framework gravel bars. In eddies, bare sand bars are replaced with vegetated bars that have a simpler topography than the pre-dam deposits.

Development of Weather-Dependent Flow Requirements for River Temperature Control.

/ Streamflow influences biological processes, habitat, and ecological integrity of streams in a number of vital ways. The establishment of weather-dependent minimum flows is essential to the protection of the aquatic environment and wildlife habitat from the adverse impacts of high water temperatures and to the effective utilization of the assimilative capacity of instream flows. In this study, weather-dependent flow requirements for summer river temperature control are derived from quantitative temperature-flow relationships. Correlation and regression of historical data and an analytical solution to the basic heat balance equation are employed to quantify the impacts of stream flow on river temperatures. Five-year continuous field measurements from the Platte River, Nebraska, USA, are used to illustrate the practical application in water-quality management. The methods and results demonstrate the feasibility of temperature control through streamflow management to meet water temperature standards and protect the aquatic biota by setting the appropriate weather-related minimum river discharges. The flow requirements are evaluated by a comparison with a critical discharge. Information provided in this paper will assist in planning streamflow regulation, design of river and reservoir operations, and application of water-quality criteria in environmental management.KEY WORDS: River discharges; Flow management; Habitat; Water quality; Weather; Wildlifehttp://link.springer-ny.com/link/service/journals/00267/bibs/24n4p529.html</HEA

THE POTENTIAL IMPACT OF CLIMATE CHANGE IN ONTARIO’S GRAND RIVER BASIN: WATER SUPPLY AND DEMAND ISSUES

The Grand River basin is expected to be one of the more sensitive areas in Ontario to the warmer and drier conditions that may result from anthropogenic climate change. The basin has a large and growing urban population, is dependent on the Grand River for wastewater assimilation and for some municipal water supplies, has experienced significant droughts in the past century, is heavily regulated, and is located well inland from alternative sources of water such as the Great Lakes. Accordingly, the Grand River basin was the chosen focus of a recent study examining the possible effects and implications of climate change and variability on water supply and demand issues. The Water Use Analysis Model (WUAM) was applied to the Grand River basin using 21 scenarios of future surface water supplies, streamflow regulation, population and water use. The ability of the system to maintain adequate streamflow (target flows) at particular sites was assessed for each scenario. Modifications to operating procedures and additional reservoir capacity were shown to be moderately successful adjustments to all but the most severe streamflow scenarios tested. Though it is difficult to justify specific adaptive measures (such as new reservoirs) based on the findings of this study alone, sufficient evidence exists to warrant further and more sophisticated assessments of climate variability and change in the Grand River basin.

Quantifying the effects of stream discharge on summer river temperature

Control of summer river temperature is needed for maintaining water temperature standards to protect aquatic biota and wildlife habitats. Given the fact that instream discharge, among meteorological and hydrological factors, may be the only one that can be practically managed, is it feasible to moderate summer river temperature through reservoir and streamflow regulations? An analysis is conducted to quantify the effects of the magnitude of instream flow on summer river temperature with weather as a reference. Relationships between water temperature and river discharge or flow depth are developed using a simplified model and adopting the concept of equilibrium temperature and bulk surface heat exchange coefficient. The relationships are validated against continuous 5-year field measurements at the central Platte River, Nebraska, USA. It was found that the variation of daily maximum water temperature with flow was stronger than that of daily mean. A critical discharge was obtained, which divides dramatic drop and slow variation in river temperature values. The existence of the critical discharge makes it possible to reduce or minimize the occurrence of daily maximum water temperature exceeding a standard at a river reach by increasing discharge to an achievable level. This study advances understanding of impacts of instream flow on summer river temperature and provides information useful in proper planning and design of reservoir operations and streamflow management.

Ice and thermal regimes on the stretch between the Ust’-Ilim hydroelectric station and mouth of the Angara River under streamflow regulation conditions

Ice and thermal regimes on the stretch between the Ust’-Ilim hydroelectric station and mouth of the Angara River under streamflow regulation conditions

Increase of the efficiency of operating the cascade of Vakhsh hydroelectric stations by using part of the runoff of the Pyandzh River

1. In connection with the historically established economic conditions and existing agreements with neighboring countries, the cascade of Vakhsh hydrostation was designed on the basis of operating conditions in an irrigation regime and cannot provide Tajikistan's own need for power in the winter, the deficit of which is 4 billion kWh/yr. The traditional methods of solving this problem call for the construction of either an irrigation reregulator in the lower course of the river or a hydrostation operating in a power compensator regime in its upper course. Both these variants require vast expenditures of material and financial resources and provide an effect just due to one particular hydro development. 2. The natural conditions of Tajikistan created the unique possibility of increasing the effectiveness of the combined operation of the Vakhsh cascade by constructing a tunnel conduit and using the runoff of the Pyandzh River in operating the Vakhsh hydrostations. With minimum construction costs the power effect of the cascade in this case increases substantially since it is achieved due to the repeated use of Pyandzh River water at all stations of the cascade and without any detriment for irrigation. 3. Realization of the proposed project will increase the total power production of the cascade for all hydrostations specified by the scheme depending on the degree of streamflow regulation by the Pyandzh reservoir. The cost effectiveness of the proposed project is an order higher than that of the traditional variants. Even for the stations operating today on the cascade its effect is comparable to the effect of the Nurek hydrostation with respect to all indices. Here the total cost of the tunnel conduit together with the dam is an order lower than the cost of the Nurek hydro development.

Comparison of recreation use values among alternative reservoir water level management scenarios

Throughout the United States, reservoirs are managed for multiple uses, including hydropower, stream flow regulation, flood control, and recreation. Water level drawdowns for hydropower, stream flow regulation, and flood control often reduce the suitability of reservoirs for water‐based recreation. The gain in aggregate economic use value of outdoor recreation under three alternative water level management scenarios was measured for four reservoirs in western North Carolina as part of an interagency policy analysis. Use values were estimated using a contingent valuation survey and expert panel data. The basic question addressed by this study was whether the value recreational users place on higher water levels held longer into the summer and fall is significantly greater than the value of using these reservoirs as they were managed at the time of this study. Maintaining high water levels for longer periods during the summer and fall was found to result in considerable gains in estimated recreational benefits. While not a primary objective of this study, having these estimates provided us an opportunity to compare increased recreational benefits with the value the Tennessee Valley Authority estimated for the reduced production of electricity that would result if the lakes were managed to hold reservoir levels higher, longer into the year.

Environmental impact assessment of the Krapivino hydro development

An environmental impact assessment of the Krapivino hydro development in may respects compelled a new look at surveying, planning, and research activities. A program of measures on restoration and protection of water resources of the Tom basin, including streamflow regulation by the Krapivino reservoir, was developed. The concept of step-by-step realization of the measures taking into account the current economic conditions was proposed. The need was found for not only a comprehensive substantiation of project studies solving problems of the region but also for special work on adaptation of the project, i.e., its coordination with all interested parties, on which realization of the project depends. Such work in our country is new for designers, surveyors, and researchers working in the sphere of hydropower construction.

ESTIMATION OF PEAK FLOWS FOR NATURAL UNGAUGED WATERSHEDS IN SOUTHERN SASKATCHEWAN

This study developed and evaluated methods to estimate peak flows from unregulated ungauged watersheds, located within the mid to southern parts of Saskatchewan, with a gross drainage area not exceeding 350 square kilometres. The analysis used annual maximum daily discharge records from thirty three currently-operated stations that were not affected by streamflow regulation. Watershed characteristics such as drainage area, drainage density, main stream slope, watershed relief and watershed shape factor were obtained for each of the thirty three basins. Single station frequency analysis of peak flows was performed on the available data of each hydrometric station. Using regression analysis, the peak flows for several return periods were related to the watershed characteristics and regression equations, related to gross and effective drainage areas, were derived for various return periods.

Groundwater discharge to a headwater valley, northwestern Nevada, U.S.A.

The role of headwater valleys within groundwater flow systems, and the manner in which gullies affect that role, need to be identified to assess the hydrologic effects of gully erosion in such valleys. This paper examines groundwater discharge to a gully in a small alluvial headwater valley in Northwestern Nevada, U.S.A., and qualitatively evaluates the effects of the gully on streamflow regulation. Field observations of groundwater flow were made during and following snowmelt in Spring 1985. Measurements of hydraulic heads were made in wells and piezometers, and groundwater discharge from the gully was measured volumetrically. Horizontal and vertical hydraulic conductivities of meadow strata were determined with field and laboratory tests. Specific conductance of gully outflow was monitored and used to estimate components of groundwater discharge with a mass-balance technique. An approximate water balance was calculated based on measured snowmelt volume, precipitation, groundwater discharge, and water-table elevations. Results indicate that despite the low primary permeability of the rhyolitic bedrock, a large proportion of groundwater discharged to the gully consists of water moving through fractures or faults in bedrock. Erosion of the gully has removed relatively low-permeability alluvium that formerly restricted groundwater discharge from the meadow. Groundwater discharge in response to snowmelt recharge is now probably more rapid and of shorter duration than prior to erosion.

Downstream of the Novosibirsk hydroelectric station on the Ob River

1. The fluvial processes in the Ob River downstream of the hydro development, which markedly changed after damming the river and creation of the reservoir during the first decade of operation of the hydrostation, were expressed in the natural process of deep erosion of the channel, which had a diminishing character. 2. Starting with the second half of the 1960s, quarrying in the Ob channel on the 30-km stretch of the lower pool adjacent to the hydrostation began to have a substantial effect on the natural process of transformation of the channel due to streamflow regulation and retention of sediments by the reservoir. 3. During the period between 1966 and 1984 more than 40 million m3 of sand-gravel mixture was removed from the river channel and floodplain in the indicated stretch, as a result of which the decrease of levels relative to the normal, natural values at the site of the Novosibirsk gauging station was 0.9–1.0 m. 4. A decrease of the levels downstream led to a deficit of water resources of the reservoir in dry years and, as a consequence, to worsening of the operating conditions of the majority of participants of the Novosibirsk water-management complex. 5. After some stabilization of the position of the levels in the river in 1984–1986, the decrease, “slump,” of the levels in the stretch passing through the city subsequently resumed beginning in 1987–1988. The rating curve for the Novosibirsk gauging station in 1988 shifted downward from the analogous 1986 curve along the height axis by 15–20 cm. 6. The priority task facing water users and consumers of Novosibirsk is the fastest possible realization of the recommendations of MGU, VNIIG, and ZapSibRNIGMI on partial restoration of the water levels in the stretch between the hydrostation and Novosibirsk city by constructing embankments damming nonnavigable branches and converting the Ob channel here at low-water discharges (less than 2000 cm3/sec) into a single-branch channel. 7. For a radical solution of the problem of reliable provision of water consumers of Novosibirsk, it is necessary to reconstruct all intakes located downstream of the hydro development.

Damming of the Irtysh River at the construction site of the Shul'binsk hydroelectric station

1. The final stage of damming the Irtysh River was carried out without complications, which was promoted by the favorable regime provided by streamflow regulation by the Bukhtarma and Ust'-Kamenogorsk reservoirs. 2. The upstream and downstream cofferdams of the pit of the first phase after their opening were subjected to intense self-erosion for several hours, and then they were dismantled by excavators and a dredge. The width of the gap on September 29, 1987 at 0800 h was respectively 107 and 125 m. The maximum depth at the site of the downstream cofferdam was 6.5–7.8 m. 3. Good dismantling of the cofferdams provided their high discharge capacity, as a consequence of which the differences of water levels and current velocities in the gap of the embankment began to decrease. In the final stage of damming the maximum velocities did not exceed 3.5 m/sec with a discharge of 73.8 m3/sec. The inflow discharge was 665 m3/sec and the final drop on the embankment was 0.67 m.

Operation of units with adjustable-blade turbines converted to a propeller regime

1. The conversion of AB turbines to a PR at all investigated hydrostations is due to equipment defects and not to economically justified considerations in connection with altered operating conditions (streamflow regulation, i.e., a decrease of the range of fluctuations of the heads; changes in the characteristic load curves, increase of requirements imposed on the reliability of power supply), i.e., it should be regarded as a forced temporary measure until reliable operation of the runner blade seals is provided. 2. The problem of providing reliable (without oil leaks) operation of AB turbine runners should be solved in the following directions: reconstruction of seals of old types by the plants and the use of superior sealing materials; retrofitting of the runner with an “oilless” hub for subsequent changing to the production of AB turbines just with runners of the modification. 3. When it is necessary to convert AB turbines to a propeller regime the cost effectiveness of this measure should be analyzed with consideration of the operating regime, and special tests should be conducted to check the guarantees of regulation and to determine the reliability in all operating regimes (starting, stopping, idling, SC regime, etc.) with measurement of vibration and wobbling of the shaft. 4. It is necessary to revise the firmly rooted practice of the unequivocal selection of AB turbines without fail for low-head hydrostations. The selection of the type of turbine for installation at hydrostations being designed or modernized with considerable daily variations of the head (1.5–2.0 m) should begin with an examination of the variant with propeller turbines as sufficiently reliable, cheap, and simple to operate. In the case of considerable seasonal variations of the head, the variant with discrete regulation of the runner blade angle is permissible. 5. For some power systems it is advisable to examine a variant with the use of two types of turbines and assignment to each type of turbine operation in its own particular zone of the load curve. This means that in the system it is necessary to have turbines with dual regulation (adjustable-blade) and more simple ones (propeller or mixed-flow), which will make it possible to avoid irrational losses of power in AB turbines at peak hours.

Streamflow Regulation and Fish Community Structure

Many regulated streams are characterized by high variable and unpredictable flow regimes. Since changes in streamflow directly modify physical habitat, streams with such highly variable flows provide highly unstable aquatic habitats. We evaluated the effect of artificial streamflow fluctuations on stream fish communities by comparing fish densities, in species and habitat groups, between two rivers differing in daily flow regime: on with with a natural flow, and one with highly regulated flows. We developed a simple model describing the relationship between available streams habitat and its use by 15 species or size classes of fish in the natural river. Species and size classes that used a specific set of microhabitat conditions were identified by comparing habitat characteristics for samples with and without each type of fish; for fish that used a particular type of microhabitat, we grouped species and size classes according to similarity in microhabitat use. Next, we categorized stream habitat samples in both the natural and regulated rivers into groups on the basis of fish habitat use criteria. Fish densities for each fish and habitat group were ten individually compared between the two rivers. An abundant (&gt;90% of all fish) and diverse (nine species) group of small—fish species and size classes were restricted to microhabitat that was characterized as shallow in depth, slow in current velocity, and concentrated along stream margins. This group of fish was reduced in abundance in the regulated river and absent at the study site with the greatest flow fluctuation. Another fish group included species and size classes that used either a broad range of habitat or a microhabitat that was deep, fast, or both, and was concentrated in midstream areas. The density of fish in this group was higher in the regulated river and peaked at the sites with the greatest fluctuations in flow. Highly variable and unpredictable flow regimes appear to be a high—frequency disturbance that effects fish differently depending on the way they use stream habitat and acts to reduce community complexity.

Consideration of bank storage when determining the power output of a hydroelectric station

1. The interaction of surface and subsurface waters increasing streamflow regulation is not taken into account in the practice of designing hydrostations. 2. The proposed method of taking it into account, realized in the form of a program of calculations with the use of computers, makes it possible to estimate the effect of the indicated factor on any planned hydropower facility. 3. A preliminary evaluation of taking into account the effect of the interaction of surface and subsurface waters for the example of a hydrostation with a seasonal reservoir made it possible to estimate it with respect to an increase of firm capacity within 0.4–0.9% and with respect to an increase of useful storage of the reservoir within 3–6%. This refinement should be added to the margin of safety of the power indices of the planned hydrostation.

Regulated scouring in a sand-bed river for channel habitat maintenance: A Platte River waterfowl case study

The planned Narrows Reservoir on the South Platte River in Colorado is expected to jeopardize the maintenance of scarce instream waterfowl habitat 400 km downstream in Nebraska's Big Bend reach of the mainstem Platte River. Extreme shrinkage of wide, shallow channel habitat for sandhill and endangered whooping cranes in the Central Flyway has resulted from past reservoir development along the North and South Platte Rivers in Wyoming and Colorado. Proposals to counteract further shrinkage caused by streamflow regulation and depletion include controlled annual peak flows designed to scour the banks, sandbars, and emerging vegetation. The criteria for effective channel maintenance by streambed scouring are examined, as well as the principles involved. The feasibility of preserving the remaining habitat by releasing scouring flows from the Narrows Dam is found seriously lacking. Alternative mechanical measures, such as dredging the channel and bulldozing the tree cover, may prove more practical, although possibly unaffordable.

Effect of hydrotechnical construction on the soil-cover complex of Riparian territories and nature conservation measures

The creation of reservoirs has a transforming effect on the landscape of river valleys in connection with a change in the earlier existing regime of surface and ground waters. Of the geological features of these valleys, the one most sensitive to a change in the regimes of flooding and moistening is the soil-cover complex, a change in the state of which makes it possible to predict subsequent links of the ecological chain and to develop nature conservation measures. In the case of stream flow regulation the greatest damage is inflicted on the soil-cover complex by flooding of territories, which leads to death of the vegetation that existed earlier. In this paper the effects of flooding and stream flow regulation as well as the resulting subirrigation by groundwater on the soil-cover complex are described and measures are developed for nature conservation in flood plains and deltas.

Maximum depth of reservoir drawdown

Calculation of the firm power of a hydrostation as a function of the drawdown depth of the reservoir, giving material for a technical and economic determination of the maximum drawdown depth, should be carried out for a prescribed power regime in the design dry year. Calculation for a prescribed discharge regime distorts the general notion about the character of this functional relation. To avoid errors in calculations of the firm capacity and power production corresponding to it as a function of drawdown depth, it is necessary to take into account thatin the case of streamflow regulation for purposes of the power industry a reservoir drawdown regime with a constant discharge is contraindicated, which should be indicated in the pertinent textbooks.

Dependence of river pollution on streamflow regulation by reservoirs

Dependence of river pollution on streamflow regulation by reservoirs