SIMULATING HYDROLOGIC AND WATER QUALITY IMPACTS IN AN URBANIZING WATERSHED1

ABSTRACT: The Hydrologic Simulation Program‐Fortran (HSPF) was calibrated and used to assess the future effects of various land development scenarios on water quality in the Polecat Creek watershed in Caroline County, Virginia. Model parameters related to hydrology and water quality were calibrated and validated using observed stream flow and water quality data collected at the watershed outlet and the outlets of two sub water sheds. Using the county's Comprehensive Plan, land use scenarios were developed by taking into account the trends and spatial distributions of future development. The simulation results for the various land use scenarios indicate that runoff volume and peak rate increased as urban areas increased. Urbanization also increased sediment loads mainly due to increases in channel erosion. Constituent loads of total Kjeldal nitrogen, orthophosphorus, and total phosphorous for Polecat Creek watershed slightly decreased under future development scenarios. These reductions are due to increases in urban areas that typically contribute smaller quantities of nitrogen and phosphorous, as compared to agricultural areas. However, nitrate loads increased for the future land use scenarios, as compared to the existing land use. The increases in nitrate loads may result from increases in residential land and associated fertilizer use and concurrent decreases in forested land. The procedures used in this paper could assist local, state, and regional policy makers in developing land management strategies that minimize environmental impacts while allowing for future development.     

CHANGES IN HYDROLOGIC RESPONSE DUE TO STREAM NETWORK EXTENSION VIA LAND DRAINAGE ACTIVITIES1

ABSTRACT: The objective of this work is to determine the effects of extension of a stream network through land drainage activities during the late 1800s on the hydrologic response of a watershed. The Mackinaw River Basin in Central Illinois was chosen as the focus and the pre‐land and post‐land drainage activity hydrologic responses were obtained through convolution of the hill slope and channel responses and compared. The hill slope response was computed using the kinematic wave model and the channel response was determined using the geomorphologic instantaneous unit hydrograph method. Our hypothesis was that the hydrologic response of the basin would exhibit the characteristic effects of settlement (i.e., increases in peak discharges and decreases in times to peak). This, indeed, is what occurred; however, the increase in peak discharges diminishes as scale increases, leaving only the decrease in times to peak. At larger scales, the dispersive effects of the longer hill slope lengths in the pre‐settlement scenario seem to balance the depressive effects of the longer path lengths in the post‐settlement scenario, thus the pre‐settlement and post‐settlement peak discharges are approximately equivalent. At small scales, the dispersion caused by the hill slope is larger in the pre‐settlement case; thus, the post‐settlement peak discharges are greater than the pre‐settlement.     

WATERSHED WEIGHTING OF EXPORT COEFFICIENTS TO MAP CRITICAL PHOSPHOROUS LOADING AREAS1

ABSTRACT: The Export Coefficient model (ECM) is capable of generating reasonable estimates of annual phosphorous loading simply from a watershed's land cover data and export coefficient values (ECVs). In its current form, the ECM assumes that ECVs are homogeneous within each land cover type, yet basic nutrient runoff and hydrological theory suggests that runoff rates have spatial patterns controlled by loading and filtering along the flow paths from the upslope contributing area and downslope dispersal area. Using a geographic information system (GIS) raster, or pixel, modeling format, these contributing area and dispersal area (CADA) controls were derived from the perspective of each individual watershed pixel to weight the otherwise homogeneous ECVs for phosphorous. Although the CADA‐ECM predicts export coefficient spatial variation for a single land use type, the lumped basin load is unaffected by weighting. After CADA weighting, a map of the new ECVs addressed the three fundamental criteria for targeting critical pollutant loading areas: (1) the presence of the pollutant, (2) the likelihood for runoff to carry the pollutant offsite, and (3) the likelihood that buffers will trap nutrients prior to their runoff into the receiving water body. These spatially distributed maps of the most important pollutant management areas were used within New York's West Branch Delaware River watershed to demonstrate how the CADA‐ECM could be applied in targeting phosphorous critical loading areas.     

REEXAMINING BEST MANAGEMENT PRACTICES FOR IMPROVING WATER QUALITY IN URBAN WATERSHEDS1

ABSTRACT: Municipalities will be implementing structural best management practices at increasing rates in their effort to comply with Phase II of the National Pollutant Discharge Elimination System (NPDES). However, there is evidence that structural best management practices (BMPs) by themselves may be insufficient to attain desired water quality standards. This paper reports on an analysis of the median removal efficiencies of structural BMPs and compares them to removal efficiencies estimated as being necessary to attain water quality standards in the Rouge River in Detroit, Michigan. Eight water quality parameters are reviewed using data collected from 1994 to 1999 in the Rouge River. Currently, five of the eight parameters in the Rouge River including bacteria, biochemical oxygen demand, and total suspended solids (TSS) exceed the required water quality standards. The reported analysis of structural BMP efficiencies reveals that structural BMPs appear capable of reducing only some of the pollutants of concern to acceptable levels.     

INFLUENCES OF WATERSHED URBANIZATION AND INSTREAM HABITAT ON MACROINVERTEBRATES IN COLD WATER STREAMS1

ABSTRACT: We analyzed data from riffle and snag habitats for 39 small cold water streams with different levels of watershed urbanization in Wisconsin and Minnesota to evaluate the influences of urban land use and instream habitat on macroinvertebrate communities. Multivariate analysis indicated that stream temperature and amount of urban land use in the watersheds were the most influential factors determining macroinvertebrate assemblages. The amount of watershed urbanization was nonlinearly and negatively correlated with percentages of Ephemeroptera‐Plecoptera‐Trichoptera (EPT) abundance, EPT taxa, filterers, and scrapers and positively correlated with Hilsenhoff biotic index. High quality macroinvertebrate index values were possible if effective imperviousness was less than 7 percent of the watershed area. Beyond this level of imperviousness, index values tended to be consistently poor. Land uses in the riparian area were equal or more influential relative to land use elsewhere in the watershed, although riparian area consisted of only a small portion of the entire watershed area. Our study implies that it is extremely important to restrict watershed impervious land use and protect stream riparian areas for reducing human degradation on stream quality in low level urbanizing watersheds. Stream temperature may be one of the major factors through which human activities degrade cold‐water streams, and management efforts that can maintain a natural thermal regime will help preserve stream quality.     

DETECTING REDUCTIONS IN SEDIMENT LOADS ASSOCIATED WITH OHIO'S CONSERVATION RESERVE ENHANCEMENT PROGRAM1

ABSTRACT: Small systematic changes in loads or concentrations of water quality constituents are difficult to detect against the background of short term fluctuations (“noise”) that result from weather and climate effects. Minimum Detectable Change Analysis (MDCA) uses prior knowledge of a water quality constituent to determine how much change must occur (e.g., from implementation of conservation practices) for the change to be statistically significant. In this paper we use MDCA to determine whether the goal of the Ohio Lake Erie Conservation Reserve Enhancement Program (CREP), to reduce sediment loads by an average of 6 percent over 10 years, represents a large enough change to be detected. We conclude that this amount of change is unlikely to be detected as statistically significant, even with the high frequency sampling program planned for evaluating it. The minimum detectable change ranges from about 7 to 9 percent for three different rivers.     

HYDROLOGIC SIMULATION OF THE LITTLE WASHITA RIVER EXPERIMENTAL WATERSHED USING SWAT1

ABSTRACT: Precipitation and streamflow data from three nested subwatersheds within the Little Washita River Experimental Watershed (LWREW) in southwestern Oklahoma were used to evaluate the capabilities of the Soil and Water Assessment Tool (SWAT) to predict streamflow under varying climatic conditions. Eight years of precipitation and streamflow data were used to calibrate parameters in the model, and 15 years of data were used for model validation. SWAT was calibrated on the smallest and largest sub‐watersheds for a wetter than average period of record. The model was then validated on a third subwatershed for a range in climatic conditions that included dry, average, and wet periods. Calibration of the model involved a multistep approach. A preliminary calibration was conducted to estimate model parameters so that measured versus simulated yearly and monthly runoff were in agreement for the respective calibration periods. Model parameters were then fine tuned based on a visual inspection of daily hydrographs and flow frequency curves. Calibration on a daily basis resulted in higher baseflows and lower peak runoff rates than were obtained in the preliminary calibration. Test results show that once the model was calibrated for wet climatic conditions, it did a good job in predicting streamflow responses over wet, average, and dry climatic conditions selected for model validation. Monthly coefficients of efficiencies were 0.65, 0.86, and 0.45 for the dry, average, and wet validation periods, respectively. Results of this investigation indicate that once calibrated, SWAT is capable of providing adequate simulations for hydrologic investigations related to the impact of climate variations on water resources of the LWREW.     

EVALUATION OF Ann AGNPS NITROGEN LOADING IN AN AGRICULTURAL WATERSHED1

ABSTRACT: Pollutants entering a water system can be very destructive to the health of that system. Best Management Practices (BMPs) are used to reduce these pollutants, but understanding the most effective practices is very difficult. Watershed models are an effective tool to aid in the decision‐making process of selecting the BMPs that are most effective in reducing the pollutant loading and are also the most cost effective. The Annualized Agricultural Nonpoint Source Pollution model (AnnAGNPS 2.0) is a technological tool that can be used to estimate watershed response to agricultural management practices. The main purpose of this paper is to test the performance of AnnAGNPS 2.0 on nitrogen loading using comparisons with measurements from the Deep Hollow watershed of the Mississippi Delta Management Systems Evaluation Area (MDMSEA) project. Previous work has demonstrated the capability of the model to simulate runoff and sediment. From sensitivity analyses in this study, initial nitrogen concentration in the soil and crop nitrogen uptake had the most impact on the nitrogen loadings. AnnAGNPS simulations of monthly nitrogen loadings are poor. However, statistical test (t‐test) showed that the predicted nitrogen loading is not significantly different from observed nitrogen loading at the 95 percent level of confidence.     

SCALE PROBLEMS IN INTERDISCIPLINARY WATER RESOURCES INVESTIGATION1

ABSTRACT The problems encountered in estimating scale parameters in interdisciplinary watershed research are discussed. Meteorology, hydrology, geology and water quality are discussed with respect to their individual strengths and weaknesses when applied to different scale problems. Areas where incompatibilities exist are pointed out and suggestions are made for effecting compromise. A watershed scale of roughly a hundred acres may be the scale at which all disciplines can effect optimum interaction.     

Livestock grazing and habitat for a threatened species: Land-use decisions under scientific uncertainty in the White Mountains,California, USA

The North Fork of Cottonwood Creek, in the White Mountains, Inyo National Forest, California, is a critically important refuge for the Paiute cutthroat trout (Oncorhynchus clarki seleniris), a federally listed threatened species. Habitat for these fish appears to be limited by excessive levels of fine sediment in the channel, and livestock grazing of riparian meadows has been implicated in delivery of sediment to the channel. However, the relationships between land use and sediment yield have not been conclusively determined, in large part because there are no historically ungrazed sites to serve as long-term controls. Accordingly, land-use decisions must be made under scientific uncertainty. To reduce erosion and sedimentation in the stream, the Forest Service spent approximately US$260,000 from 1981 to 1991 to repair watershed damage from livestock grazing, prevent livestock from traversing steep banks, and limit livestock access to the channel. Throughout this period, livestock grazing has continued on these lands, yielding less than $12,000 in grazing fees. In revising its Allotment Management Plan for the basin, the Forest Service rejected the “no-grazing” alternative because it was inconsistent with its Land and Resource Management Plan, which specifies there is to be no net reduction of grazing. Joint appointment with the University of California White Mountain Research Station, East Line Street, Bishop, California 93518, USA.