Low Flow Years Research Articles

Anthropogenic and climatic influences on the eutrophication of large estuarine ecosystems

We examined the effects of anthropogenic and climatic perturbations on nutrient—phytoplankton interactions and eutrophication in the waters of the largest estuarine systems in the U.S.A., the Chesapeake Bay (CB), Maryland/ Virginia, and the Neuse River Estuary/Pamlico Sound (NRE/PS) system, North Carolina. Both systems have experienced large post‐World War II increases in nitrogen (N) and phosphorus (P) loading, and nutrient reductions have been initiated to alleviate symptoms of eutrophication. However, ecosystem‐level effects of these nutrient reductions are strongly affected by hydrologic variability, including severe droughts and a recent increase in Atlantic hurricane activity. Phytoplankton community responses to these hydrologic perturbations, including storm surges and floods, were examined and when possible, compared for these systems. In both systems, the resulting variability in water residence time strongly influenced seasonal and longer‐term patterns of phytoplankton biomass and community composition. Fast‐growing diatoms were favored during years of high discharge and short residence time in CB, whereas this effect was not observed during high discharge conditions in the longer residence time NRE/ PS. In the NRE/PS, all phytoplankton groups except summer cyanobacterial populations showed decreased abundance during elevated flow years when compared to low flow years. Although hurricanes affected the CB less frequently than the NRE/PS, they nonetheless influenced floral composition in both systems. Seasonally, hydrologic perturbations, including droughts, floods, and storm‐related deep mixing events, overwhelmed nutrient controls on floral composition. This underscores the difficulty in predicting seasonal and longer‐term phytoplankton production and compositional responses to nutrient input reductions aimed at controlling eutrophication of large estuarine ecosystems.

Cash Flow Sensitivity of Investment

Investment cash flow sensitivity is associated with both undervestment when cash flows are low and overinvestment when cash flows are high. The accessibility of external capital is positively correlated with cash flows, intensifying investment cash flow sensitivity. Managers actively counteract the variations in internal and external liquidity by accumulating working capital when liquidity is high and draining it when liquidity is low. These results imply that cash flow sensitive firms face financial constraints, which are binding in low cash flow years. While financial constraints have an economically significant impact on investment timing, cash flow sensitive firms alleviate their effects and, actually, overinvest, on aggregate.

Optimal Water Allocation for the Transboundary Subernarekha River, India

This paper presents a linear programming model for optimal water allocations in a large river basin system. The model is applied to the transboundary Subernarekha River in India, which has two main stream reservoirs, two barrages, and three small command area reservoirs. The Tripartite Agreement (TPA) among the cobasin riparian states for sharing of its waters is analyzed. The main objective is to find the maximum annual benefits from irrigation and hydropower subject to various constraints on the system. Design constraints as per the TPA relating to the water shares among riparian states (i.e., Bihar, Orissa, and West Bengal) at individual dams and barrages are also considered. Optimal water allocations are obtained based on the 75% water year dependable flow as specified in the TPA. Water shortage and water surplus years have also been considered to determine optical water allocations during the dry and wet years, respectively. The stream reservoirs Chandil and Icha would fail to meet the water demands during the low flow years, whereas the Kharkai and Galudih barrages would essentially satisfy water demands according to the TPA provisions. Results indicate that Bihar is likely to benefit most from the TPA.

The coherent variability of African river flows : composite climate structure and the Atlantic circulation

The composite structure of the ocean and atmosphere around Africa is studied in the context of river flow variability. Annual streamflows are analysed for the Blue and White Nile, Congo, Niger, Senegal, Zambezi, and Orange Rivers, and inflow to Lake Malawi. Spectral energy is concentrated in 6.6- and 2.4-year bands. The interannual variability of many river flows is significantly cross-correlated (p < .05) over the period 1950-1995, following removal of the mean trend. A combined river flow index indicates that flows were highest in 1961, 1962, 1968, 1977, 1978 and lowest in 1971, 1972, 1982, 1983, 1991. Forming a composite of differences between high- and low-flow years, SST anomalies and other atmospheric fields are investigated to better understand climatic factors driving hydrological extremes. During high flows, NCEP reanalysis data reveal a composite La Nina event off Peru-Ecuador. SST patterns reveal an inter-hemispheric dipole in the Atlantic (eg. warm - north) and below normal SST in the west Indian Ocean during years with high flow. The equatorial east Atlantic undergoes warming through the ‘composite year’ in a manner consistent with its opposing response to the Indo-Pacific La Nina. Tropical upper winds are easterly and symmetrical about the equator, and may explain why inter-annual variability of river flows south of the equator are correlated with those of the north at 6-month lag. Low level westerly winds are greater during high flow years, particularly along the Guinea coast. Differences of OLR and upper velocity potential demonstrate two distinct centers of action either side of the tropical Atlantic. It is concluded that hydrological events over Africa and South America are sensitive to tropical Atlantic coupling with the global El Nino – Southern Oscillation signal.

Mechanistic Linkage of Hydrologic Regime to Summer Growth of Age-0 Atlantic Salmon

Significant reductions in juvenile stream salmonid growth have been observed in association with low summer flow, but underlying mechanisms are poorly understood and predictive power is limited. We conducted a stage-specific analysis of the relationship between summer flow and the growth of age-0 Atlantic salmon Salmo salar in two rearing sites in the upper Connecticut River basin, New Hampshire. We contrasted effects of variation in foraging habitat availability and temperature on individual age-0 Atlantic salmon mass during one high-flow year and two low-flow years and from high- and low-flow sites within years. Overall age-0 Atlantic salmon mass was positively correlated with the availability of model-predicted favorable foraging locations and negatively correlated with density during the summer. Individual Atlantic salmon mass and the proportion of temperature-predicted maximum mass were lowest during the two low-flow years and were lower in upstream than in downstream sections. Between-year variation in growth was not closely associated with temperature model predictions. However, some of the difference between upstream and downstream sections appeared to be associated with lower summer temperatures in the upstream section. Our case study provides a framework for combining empirical and modeling approaches to quantify the potential impact of hydrologic change on fish growth and for linking variation in stream discharge to juvenile Atlantic salmon performance across time and space.

Streamflow in the Mackenzie Basin, Canada

Rivers of the Mackenzie Basin exhibit several seasonal flow patterns that include the nival (snowmelt dominated), proglacial (influenced by glacier melt), wetland, prolacustrine (below large lakes), and regulated flow regimes. The Mackenzie amalgamates and moderates these regimes to deliver spring peak flows, followed by declining summer discharge and low winter flows, to the Arctic Ocean. The mountainous sub-basins in the west (Liard, Peace, and northern mountains) contribute about 60% of the Mackenzie flow, while the interior plains and eastern Canadian Shield contribute only about 25%, even though the two regions have similar total areas (each occupying about 40% of the total Mackenzie Basin). The mountain zone is the dominant flow contributor to the Mackenzie in both high-flow and low-flow years. A case study of the Great Slave system demonstrates the effects of natural runoff, regulated runoff, and lake storage on streamflow, as well as the large year-to-year variability of lake levels and discharge. Despite a warming trend in the past three decades, annual runoff of the Mackenzie Basin has not changed. Significant warming at most climatic stations in April (and at some, also in May or June) could have triggered earlier snowmelt. The first day of hydrograph rise for the main trunk of the Mackenzie (seen as a proxy for breakup) has advanced by about three days per decade, though the trend was not statistically significant for the mountain rivers. Peak flows do not reveal any trend, but the arrival of the spring peaks has become more variable. More evidence is needed to interpret these flow phenomena properly.

Plasma insulin-like growth factor-I concentrations in yearling chinook salmon (Oncorhynchus tshawytscha) migrating from the Snake River Basin, USA

During the parr-to-smolt transformation (smoltification) of juvenile salmonids, preadaptive changes in osmoregulatory and ionoregulatory ability are regulated in part by the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. If food intake is sufficient, plasma IGF-I increases during smoltification. On the other hand, plasma IGF-I typically decreases in fasting fish and other vertebrate animals. Because food availability is limited for juvenile salmonids undertaking an extended 6- to 12-week springmigration to and through the Snake-Columbia River hydropower system (northwestern USA), IGF-I concentrations might be expected to decrease, potentially compromising seawater tolerance. To address this possibility,yearling chinook salmon Oncorhynchus tshawytscha reared in three Snake River Basin hatcheries were sampled before release and at two downstream dams. Dry masses ofmigrating fish either did not increase during themigration (in 2000, an average-flow year), or decreased significantly (in 2001, a low-flow year). In both years, plasma IGF-I levels were significantly higher (1.6-fold in 2000, 3.7-fold in 2001) for fish sampled at the last dam on the lower Columbia River than for fish sampled prior to release. Plasma IGF-I concentrations inmigrating fish may, nonetheless, have been nutritionally down-regulated to some degree, because plasma IGF-I concentrations in juvenile chinook salmon captured at a Snake River dam and transported to the laboratory increased in fed groups, but decreased in unfed groups. The ability ofmigrating smolts to maintain relatively elevated IGF-I levels despiteRestricted food intake and loss of body mass is likely related to smoltification-associated changes in hormonal balance.

The biogeochemistry of Si in the McMurdo Dry Valley lakes, Antarctica

The biogeochemical dynamics of Si in temperate lakes is well documented and the role of biological uptake and recycling is well known. In this paper we examine the Si dynamics of a series of ice-covered, closed-basin lakes in the McMurdo Dry Valley region (~78° S) of Antarctica. Our data and calculations indicate that biological uptake of Si is not a major process in these lakes. Mass balance considerations in Lake Hoare, the youngest and the freshest lake, suggest that annual stream input during relatively low-flow years is minor and that Si dynamics is greatly influenced by hydrological variation and hence climatic changes affecting stream flow and lake level. The data imply that the Si input during high-flow years must dominate the system. Subtle changes in climate have a major control on Si input into the lake, and Si dynamics are not controlled by biogeochemical processes as in temperate systems.

TMDLS: Statistical Correlations or Mechanistic Modeling?

In developing TMDL waste-load allocations for the Snake River-Reservoir system in Western Idaho and Eastern Oregon, determinations of the assimilative capacity of the system and the impact of pollutant reduction strategies has been performed using both a statistical-correlation approach and a mechanistic modeling approach. The system included the Lower Snake River, Brownlee Reservoir, Oxbow Reservoir, and Hells Canyon Reservoir with the focus was on Brownlee Reservoir. The statistical approach used on Brownlee Reservoir divided the system into riverine and lacustrine zones. Field data were then averaged over season and location to provide statistical correlations, such as between total phosphorus (TP) and chlorophyll a (chl a), between an anoxic factor (AF) and TP, and between a hypoxic factor (HP) and TP. The anoxic factor is defined as the number of days when dissolved oxygen was less than 2 mg/l and the hypoxic factor was defined as the number of days when dissolved oxygen was less than 6.5 mg/l. The mechanistic approach used a two-dimensional, unsteady, hydrodynamic and water quality model called CE-QUAL-W2. The model was calibrated to field data over a three year period for 1992 (a low flow year), 1995 (an average flow year), and 1997 (a high flow year). Some of the important questions that the TMDL process was to answer included the following. What level of TP is necessary in the river coming into Brownlee Reservoir to reduce the number of days of hypoxia in the reservoir? What are the causes of low-

Effect of small catchment dams on downstream vegetation of a seasonal river in semi‐arid African savanna

1 Seasonal rivers in semi-arid African savannas support riparian woodland and hydromorphic grassland, key habitats for wildlife or livestock. We investigated the effect of numerous, small, agricultural dams built on low-order streams within the Kolope–Setonki subcatchment of the Limpopo river. We examined how reducing or changing the pattern of water flow in the main rivers will affect the riparian or hydromorphic vegetation. 2 Existing hydrological models demonstrate a mean annual water flow of 7·6 × 106 m3, ranging from zero to 215 × 106 m3. The catchment area affected by agricultural dams increased from 2% to 50% between 1955 and 1987. Dams are believed to have curtailed the flow during years of low flow. 3 The water requirement of four key species was assessed from their elevation above and distance from the river such that Faidherbia albida > Schotia brachypetala ~ Xanthocercis zambesiaca > Combretum imberbe. This order did not accord with the relative degree of mortality and canopy dieback. Twenty-nine per cent of F. albida trees were dead and the remainder had lost an average of 31% of canopy volume; S. brachypetala and X. zambesiaca exhibited negligible dieback and no mortality; whereas 10% of C. imberbe were dead and the remainder had lost an average of 8% of canopy volume. 4 Tree size and water availability influenced mortality and canopy dieback of F. albida and C. imberbe. Mortality of F. albida affected trees of all except the smallest size, although dead trees were on average larger than living trees. Dead trees of C. imberbe were at a greater elevation above or distance from the river. The likelihood of F. albida experiencing dieback was greater at higher elevations above the river and for larger trees, whereas that of C. imberbe was greater at greater distances from and higher elevations above the river if a tree was large. 5 Woody cover on hydromorphic grasslands, mainly of Acacia tortilis, increased from 8% to 37% between 1955 and 1987. Most of the increase occurred between 1965 and 1977, coincident with the extended 1960s drought and the above-average rainfall of the 1970s in a system that had been exposed to sustained, severe grazing by livestock. 6 The cumulative impact of many small farm dams on downstream rivers is apparently to reduce flow during critical dry years to levels causing dieback of F. albida and C. imberbe and desiccation of hydromorphic grassland. The water requirements of this vegetation need to be determined for policy makers to address the conflicting water needs of agriculture and indigenous vegetation.

Retention of White Perch and Striped Bass Larvae: Biological-Physical Interactions in Chesapeake Bay Estuarine Turbidity Maximum

Physical and biological properties of the Chesapeake Bay estuarine turbidity maximum (ETM) region may influence retention and survival of anadromous white perch (Morone americana) and striped bass larvae (Morone saxatilis). To evaluate this hypothesis we collected data in five cruises, three during May 1998 and two during May 1999, in upper Chesapeake Bay. Time series of freshwater discharge, water temperature, wind, and water level explain differences in ETM location and properties between cruises and years. During high flows in 1998, a two-layer response to wind forcing shifted the ETM up-estuary, while a high discharge event resulted in a down-estuary shift in the salt front and ETM location. In 1999, extremely low discharge rates shifted the salt front 15 km up-estuary of its position in 1998. During 1999, the ETM was less intense and apparently topographically fixed. Gradients in depth-specific abundance of ichthyoplankton were compared with salinity and TSS concentrations along the channel axis of the upper Bay. During 1998, the high flow year, most striped bass eggs (75%) and most early-stage white perch larvae (80%) were located up-estuary of the salt front. In addition, most striped bass (91%) and white perch (67%) post-yolk-sac larvae were located within 10 km of maximum turbidity readings. Total abundance of white perch larvae was lower in 1999, a low freshwater flow year, than in 1998, a high flow year. In 1999, striped bass larvae were virtually absent. White perch (1977–1999) and striped bass (1968–1999) juvenile abundances were positively correlated with spring Susquehanna River discharge. The ETM regions is an important nursery area for white perch and striped bass larvae and life-history strategies of these species appear to insure transport to and within the ETM. We hypothesize that episodic wind and discharge events may modulate larval survival within years. Between years, differences in freshwater flow may influence striped bass and white perch survival and recruitment by controlling retention of egg and early-stage in the ETM region and by affecting the overlap of temperature/salinity zones preferred by later-stage larvae with elevated productivity in the ETM.

Nitrogen budget in the Upper Mississippi River watershed

Abstract Nitrogen budget calculations performed for highflow and low-flow years in the major sub-basins of the Upper Mississippi River watershed show differences in nitrogen applications and discharges. Nitrogen budgets show that fertilizer is the most important input of nitrogen to the basins, but also show that atmospheric input and animal manures can be significant inputs of nitrogen to the basins. The transport of nitrogen from the land to rivers varies with the prevailing hydrologic conditions. The annual nitrogen budgets are not balanced. In years of high precipitation and river discharge, more nitrogen can be removed than had been applied that year, presumably from N stored in the soil or ground water. Storage of nitrogen in soils is a major unknown in the model, but calculations suggest that it is a significant reservoir of N.

Classification of river regimes: a context for hydroecology

Over the past 30 years, ecologists have demonstrated the importance of flow and temperature as primary variables in driving running water, riparian and floodplain ecosystems. As it is important to assess the size and timing of discharge variations in relation to those in temperature, a method is proposed that uses multivariate techniques to separately classify annual discharge and temperature regimes according to their ‘shape’ and ‘magnitude’, and which then combines the classifications. This paper: (i) describes a generally applicable method; (ii) tests the method by applying it to riparian systems on four British rivers using a 20-year record (1977–97) of flow and air temperature; (iii) proposes a hydroecological interpretation of the classification; (iv) considers the degree to which the methodology might provide information to support the design of ecologically acceptable flow regimes. ‘Regimes’ are defined for discharge and air temperature using monthly mean data. The results of applying the classification procedure to four British rivers indicates that the ‘typical’ regimes for each of the four catchments are composite features produced by a small number of clearly defined annual types that reflect interannual variability in hydroclimatological conditions. Annual discharge patterns are dominated by three ‘shape’ classes (accounting for 94% of the station years: class A, early (November) peak; class B, intermediate (December–January) peak; and class C, late (March) peak) and one ‘magnitude’ class (70% of the station years fall into class 3, intermediate), with two subordinate ‘magnitude’ classes: low-flow years (18%) and high flow years (12%). For air temperature, annual patterns are classified evenly into three ‘shape’ and four ‘magnitude’ classes. It is argued that this variety of flow–temperature patterns is important for sustaining ecosystem integrity and for establishing benchmark flow regimes and associated frequencies to aid river management. Copyright © 2000 John Wiley & Sons, Ltd.

Classification of river regimes: a context for hydroecology

Over the past 30 years, ecologists have demonstrated the importance of flow and temperature as primary variables in driving running water, riparian and floodplain ecosystems. As it is important to assess the size and timing of discharge variations in relation to those in temperature, a method is proposed that uses multivariate techniques to separately classify annual discharge and temperature regimes according to their shape and magnitude, and which then combines the classifications. This paper: (i) describes a generally applicable method; (ii) tests the method by applying it to riparian systems on four British rivers using a 20-year record (1977-97) of flow and air temperature; (iii) proposes a hydroecological interpretation of the classification; (iv) considers the degree to which the methodology might provide information to support the design of ecologically acceptable flow regimes. Regimes are defined for discharge and air temperature using monthly mean data. The results of applying the classification procedure to four British rivers indicates that the typical regimes for each of the four catchments are composite features produced by a small number of clearly defined annual types that reflect interannual variability in hydroclimatological conditions. Annual discharge patterns are dominated by three shape classes (accounting for 94% of the station years: class A, early (November) peak; class B, intermediate (December-January) peak; and class C, late (March) peak) and one magnitude class (70% of the station years fall into class 3, intermediate), with two subordinate magnitude classes: low-flow years (18%) and high flow years (12%). For air temperature, annual patterns are classified evenly into three shape and four magnitude classes. It is argued that this variety of flow-temperature patterns is important for sustaining ecosystem integrity and for establishing benchmark flow regimes and associated frequencies to aid river management.

The effect of glacier wastage on the flow of the Bow River at Banff, Alberta, 1951–1993

A surface area/volume relationship was used to estimate total glacier volumes for the highly glacierized Hector Lake Basin (281 km2) in the Canadian Rockies in the years 1951 and 1993. The change in volume was calculated and this value then extrapolated up to the Bow Basin at Banff (2230 km2) based on relative proportions of glacier cover. The mean net glacier volume loss estimate of 934×106 m3 was divided into annual proportions of glacier wastage and storage using a local mass balance record collected at Peyto Glacier in the Mistaya Valley, contiguous to the Bow Basin. Unfortunately, the record began in 1966 and a hind-cast to 1952 (hydrological year) was necessary. Banff maximum summer temperature and Lake Louise snow course data were used as surrogates for summer and winter glacier mass balance, respectively. Monthly wastage proportions were estimated for 1967–1974 by using modelled values of glacial melt as a template. Glacier wastage inputs to and storage held back from the Bow River hydrograph at Banff were compared with known basin yields to assess the hydrological effects of glacier volume change. For 1952–1993, the average annual wastage/basin yield ratio was found to be around 1·8%. For the extremely low flow year of 1970 this ratio increased to 13%. The proportion of flow derived from glacier wastage in August of this year was estimated to be around 56%. Although the results tend to confirm the regulatory effect of glaciers on stream flow, it was found that in some years of low flow this situation has been aggravated by water being held in glacial storage. © 1998 John Wiley & Sons, Ltd.

Function and dynamics of woody debris in stream reaches in the central Sierra Nevada, California

In 1993, we located, measured, and tagged almost 1700 woody debris pieces on six streams in California’s central Sierra Nevada. The stability, geomorphic function, and use by fish for cover of each piece were recorded. In 1994 and 1995, piece movement was quantified and new debris pieces were measured. In the 60 study reaches, debris was not influential in shaping channel morphology and fish cover. Although woody debris was often associated with habitat units, few pieces deflected flow or contributed to the formation of pools or steps. Fish used deep water as cover more often than debris or any other cover type. Medium-sized debris was, however, used in a greater proportion than its availability to fish. Little sediment was stored by debris, and five large pieces stored 85% of the sediment volume measured. Debris frequency and volume did not differ significantly by channel type. After a low stream flow year (1993–1994), few pieces had moved and few new pieces were identified. After a high-flow season (1994–1995), 31% of the pieces had either moved or were not found and new pieces represented over 5% of the originally surveyed volume of wood.

Factors Governing Macrophyte Status in Hampshire Chalk Streams: Implications for Catchment Management

AbstractSevere droughts in the late 1980s and 1990s have highlighted the fragility of many aquatic environments in southern England; in particular, declining river flows may be having an adverse affect on macrophytes in the chalk‐fed streams of the Rivers Test and Itchen. Detailed macrophyte survey data which were collected from representative sites in both rivers during 1991–1995 are interpreted in the context of changing hydroclimatic, water quality and in‐stream channel conditions. Multivariate statistical analyses support the assertion that river flow is the most significant parameter governing observed changes in macrophyte cover. During low flow years, filamentous algae have increased at most sites to the detriment of Ranunculus spp. These findings have catchment‐management implications which should be addressed if the long‐term integrity of such aquatic ecosystems is to be safeguarded.

Production and Loss of Methylmercury and Loss of Total Mercury from Boreal Forest Catchments Containing Different Types of Wetlands

Four terrestrial boreal forest catchments containing different types of wetlands were studied to determine their strength as sources or sinks of methylmercury (MeHg) and total mercury (THg) to downstream ecosystems and to determine if patterns seen in one year were consistent over several years. All catchments were sinks for THg. The wetland type, percentage wetland area (0−25%), or annual water yield did not appear to have a consistent effect on the magnitude of this retention. Wetland areas of the catchments were always net sources of MeHg. Unlike for THg, there were large and consistent differences in the source strength among wetland types for MeHg. These differences appeared to be related to differences in the internal hydrology of the wetlands. All types of wetlands were greater sources of MeHg during years of high water yield, but even during years of low flow all wetland types were sources of MeHg. Thus, we conclude that wetlands are important sites of MeHg production in boreal ecosystems on the l...

The role of vegetation and bed-level fluctuations in the process of channel narrowing

A catastrophic flood ire 1965 on Plum Creek, a perennial sandbed stream in the western Great Plains, removed most of the bottomland vegetation and transformed the single-thalweg stream into a wider, braided channel. Following eight years of further widening associated with minor high flows, a process of channel narrowing began in 1973; narrowing continues today. The history of channel narrowing was reconstructed by counting the annual rings of 129 trees and shrubs along a 5-km reach of Plum Creek near Louviers, Colorado. Sixty-three of these plants were excavated in order to determine the age and elevation of the germination point. The reconstructed record of channel change was verified from historical aerial photographs, and then compared to sediment stratigraphy and records of discharge and bed elevation from a streamflow gaging station in the study reach. Channel narrowing at Plum Creel: occurs in two ways. First, during periods of high flow, sand and fine gravel are delivered to the channel, temporarily raising the general bed-level. Subsequently, several years of uninterrupted low flows incise a narrower channel. Second, during years of low flow, vegetation becomes established on the subaerial part of the present channel bed. In both cases, surfaces stabilize as a result of vegetation growth and vertical accretion of sediment.

Ecological–economic assessment of a sediment‐producing stream behind lower granite dam on the lower snake river, USA

AbstractField investigations and simulation modelling studies were conducted on an agriculturally perturbed watershed draining into the regulated Lower Clearwater–Snake Rivers of Idaho and Washington. Ecological–economic analyses were conducted to develop an integrated systems framework to assess the impacts of alternative farming practices on sustainable farming, sediment erosion and stream health on Tom Beall Creek, with ecological implications and consequences to Lower Granite Reservoir on the Snake River. A geographic information system (GIS) was used to spatially delineate field boundaries, soil types, drainage patterns and erosion rates. An AGNPS (agricultural nonpoint source) pollution model was interfaced with the GIS to project water quality impacts of land use in the watershed. The AGNPS model was integrated with a mixed integer linear programming model (MIP) to facilitate modelling cost effectiveness on land as it related to eroded soil entering the receiving streams. Biological health assessment was performed using benthic macroinvertebrates. The biological condition of Tom Beall Creek was rated as slightly and moderately impaired for 1992 and 1993, respectively. A wheat–pea rotation under conventional tillage and cross‐slope farming had the highest weighted average on‐site erosion damage of $20 per ha; the lowest damage was $3.63 per ha using a wheat–barley–fallow rotation with reduced tillage and divided slopes. Simulating a ‘no programme’ policy scenario, the MIP model showed the dramatic impact of the current farm programme with conservation compliance in the region of highly erodible land and high participation rate in the government farm programme. Under current farming practices and &gt; 50 yr spring runoff event, it was estimated that nearly 5000 t of suspended solids would be exported from the Tom Beall watershed. During low flow years, less than 200 t were exported.Sedimentation in Tom Beall Creek is the most debilitating environmental factor impacting the aquatic biota. High erosion rates from all of the anthropogenically impacted streams above Lower Granite Dam tend to shorten the productive storage life of the reservoir, alter the hydroelectric power generating capacity and interfere with the ecological food web and biodiversity. Although the implementation of better conservation practices in anthropogenically disturbed watersheds will not eliminate watershed erosion, it will reduce the frequency and the amounts of sediment dredged from reservoirs in the future, and will reduce on‐site and off‐site costs of erosion and sediment damage.