North Bosque River Research Articles

REGRESSION-BASED FLOW ADJUSTMENT PROCEDURES FOR TREND ANALYSIS OF WATER QUALITY DATA

Trend analysis is an important component of most total maximum daily load (TMDL) projects in assessing the adequacy of implementation plans on water quality improvement. One problem in trend analysis of water quality data is the confounding effect of varying streamflow conditions at the time of sampling. Commonly used methods of flow adjustment are ordinary least squares (OLS) regression and locally weighted regression and smoothing scatterplots (LOWESS) with a prespecified smoothing factor (f) of 0.5. We compared trend analysis results using these two methods of flow adjustment as well as LOWESS flow adjustment approach with the optimal f value based upon the bias corrected Akaike information criterion (AICc1). The objectives of the study were to evaluate the importance of flow adjustment in trend analysis and to determine the best flow adjustment method among these three procedures. Monthly concentrations from grab and flow-weighted data sets of soluble orthophosphate-phosphorus (PO4-P), total P (TP), and total suspended solid (TSS) were evaluated for three stream sites within the North Bosque River watershed in central Texas. The nonparametric Kendall statistic was employed to test for the presence of trend. As expected, the detection of trend was greatly influenced by flow adjustment. The LOWESS procedure was considered more appropriate than OLS, because LOWESS was able to better define the relationships between flow and constituent concentration. The AICc1 based f value and f = 0.5 in the LOWESS procedure gave similar trend results indicating that the default f value of 0.5 is adequate for reducing variability in constituent concentrations due to flow.

INTEGRATION OF WATERSHED TOOLS AND SWAT MODEL INTO BASINS1

ABSTRACT: BASINS (Better Assessment Science Integrating Point and Nonpoint Sources) version 3.0, is the updated software system developed by the U.S. Environmental Protection Agency Office of Water in order to meet the requirements of developing Total Maximum Daily Load (TMDL) programs. BASINS provides an enhanced set of nation‐wide databases, several new and interchangeable tools and models integrated in a new modular architecture, operating within ArcView Geographical Information System (GIS) for desktop PCs. This paper describes the integration of three new key components: (1) a tool that optimizes the automatic definition and segmentation of the watershed and stream network based on topography (Digital Elevation Models), NHD (National Hydrography Dataset) or other ancillary stream data; (2) a tool to define the Hydrologic Response Units (HRUs) over the watershed and subwatersheds; and (3) SWAT (Soil and Water Assessment Tool) model and a respective integrated user‐friendly interface. The first two components, based on raster functionality, improve the previously adopted simplistic methods for the hydrologic definition, segmentation and basic geomorphic assessment of the watershed and open to the usage of external datasets besides those distributed with the whole BASINS package. In addition, these components share generating datasets, hereby promoting the usage by other tools and models as well as other models that in the future could be introduced in BASINS. The third component introduces the SWAT model into BASINS. SWAT is a hydrologic distributed model with proven success in watershed assessment of both agricultural and urban scenario management effects on water quality and is based on over 30 years of USDA modeling experience. The description of these integrated components is followed by a simple, yet promising, application to the Upper North Bosque River watershed in Texas, using the default data distributed with BASINS.

VALIDATION OF THE SWAT MODEL ON A LARGE RWER BASIN WITH POINT AND NONPOINT SOURCES1

ABSTRACT: The State of Texas has initiated the development of a Total Maximum Daily Load program in the Bosque River Watershed, where point and nonpoint sources of pollution are a concern. Soil Water Assessment Tool (SWAT) was validated for flow, sediment, and nutrients in the watershed to evaluate alternative management scenarios and estimate their effects in controlling pollution. This paper discusses the calibration and validation at two locations, Hico and Valley Mills, along the North Bosque River. Calibration for flow was performed from 1960 through 1998. Sediment and nutrient calibration was done from 1993 through 1997 at Hico and from 1996 through 1997 at Valley Mills. Model validation was performed for 1998. Time series plots and statistical measures were used to verify model predictions. Predicted values generally matched well with the observed values during calibration and validation (R2≥ 0.6 and Nash‐Suttcliffe Efficiency ≥ 0.5, in most instances) except for some underprediction of nitrogen during calibration at both locations and sediment and organic nutrients during validation at Valley Mills. This study showed that SWAT was able to predict flow, sediment, and nutrients successfully and can be used to study the effects of alternative management scenarios.

DETERMINING NUTRIENT EXPORT COEFFICIENTS AND SOURCE LOADING UNCERTAINTY USING IN‐STREAM MONITORING DATA1

ABSTRACT: Over a three‐year period, flow and nutrients were monitored at 13 sites in the upper North Bosque River watershed in Texas. Drainage areas above sampling sites differed in percent of dairy waste application fields, forage fields, wood/range, and urban land area. A multiple regression approach was used to develop total phosphorus (TP) and total nitrogen (TN) export coefficients for the major land uses in these heterogeneous drainage areas. The largest export coefficients were associated with dairy waste application fields followed by urban, forage fields, and wood/range. An empirical model was then established to assess nutrient contribution by major sources using developed export coefficients and point source loadings from municipal wastewater treatment. This model was verified by comparison of estimated loadings to measured in‐stream data. Monte Carlo simulation techniques were applied to provide an uncertainty analysis for nutrient loads by source, based on the variance associated with each export coefficient. The largest sources of nutrients contributing to the upper North Bosque River were associated with dairy waste application fields and forage fields, while the greatest relative uncertainty in source contribution was associated with loadings from urban and wood/range land uses.

APPLICATION OF A WATERSHED MODEL TO EVALUATE MANAGEMENT EFFECTS ON POINT AND NONPOINT SOURCE POLLUTION

A Total Maximum Daily Load (TMDL) program has been initiated in the North Bosque River Watershed in Texas, USA, where point and nonpoint sources of pollution are of a concern. The Soil and Water Assessment Tool (SWAT), which had been validated for flow and sediment and nutrient transport, was applied to quantify the effects of Best Management Practices (BMPs) related to dairy manure management and municipal wastewater treatment plant effluent. Results are presented for the period from 1960 through 1998 for three sites along the North Bosque River. Results are presented as annual time–weighted concentrations (average of the daily load divided by daily flow over a year) and annual flow–weighted concentrations (total cumulative load divided by total cumulative flow over a year). The wastewater treatment plant BMPs resulted in greater improvement in time–weighted instream soluble phosphorus concentrations than dairy BMPs. On the other hand, dairy BMPs made greater differences in flow–weighted concentrations. This study showed that SWAT could be a useful tool for studying the effects of alternative management scenarios for pollution control from point and nonpoint sources in large watersheds.

Relating Agricultural Land Uses to In‐Stream Stormwater Quality

AbstractSixteen largely agricultural watersheds in the upper portion of the North Bosque River of central Texas were instrumented to collect storm event samples for nutrient analysis. Flow‐weighted storm‐event mean concentrations were averaged across storm events to characterize the water quality at each site for storms sampled between November 1992 and August 1995. Nutrient concentrations were related to land uses above sampling sites using correlation and regression analysis to indicate major sources of nutrient nonpoint source pollution to the upper North Bosque River. Consistently, N and P concentrations increased as the proportion of land area used for dairy waste application fields (or milking cow densities) increased in the drainage basins above sampling sites. The proportion of total P (TP) in runoff represented by soluble reactive P (SRP) also increased as the percent of dairy waste application fields above a sampling site increased; likely as a response to the common practice of surface application of manure to permanent pasture. This increase in SRP is of particular importance because SRP is readily bioavailable in aquatic systems, thus increasing the potential for accelerated eutrophication in receiving waterbodies. The results of these analyses indicate a strong association between in‐stream nutrient concentrations during storm events and the percent of dairy waste application fields comprising a drainage area. This indicates a need to manage the movement of nutrients, particularly soluble P, from manure application fields in areas where in‐stream nutrient levels are considered a nonpoint source pollution problem.