Little Washita River Experimental Watershed Research Articles

Relationship of arsenic and chromium availability with carbon functional groups, aluminum and iron in Little Washita River Experimental Watershed Reservoirs, Oklahoma, USA

Sediment from three reservoirs located in the Little Washita River Experimental Watershed (LWREW) in Oklahoma, USA with contrasting dominant land uses were analyzed for total and extractable concentrations of arsenic (As) and chromium (Cr), and the potential ecologic risk to benthic organisms. Extractable As ranged from 0.24 to 1.21 mg kg−1, in the order grazing>cropland>forest and 0.13–0.58 mg kg−1 for extractable Cr, in the order of forest>grazing>cropland. However, only approximately < 1.5% of total As and < 4% of total Cr were extractable. Total As ranged from 16.2 to 141 mg kg−1 and total Cr ranged from 5.06 to 40.1 mg kg−1 both in the order of cropland>grazing>forest. The sediment exhibited an alkaline pH (8.0–8.7). As sorption exhibited a positive relationship with Al (r = 0.9995; P = 0.0001), Fe (r = 0.9829; P = 0.0001), and C (r = 0.4090; P = 0.0017) and Cr correlated positively with Al (r = 0.9676 P = 0.0001), Fe (r = 0.9818; P = 0.0001), and C (r = 0.3368; P = 0.0111). In addition, both As and Cr exhibited positive relationships with carbon (C) functional groups in the order of O-alkyl C> methoxyl C> alkyl C> aromatic C> carboxyl C> phenolic C. The sediment concentration analysis results illustrated that As in all reservoirs exceeded their respective Threshold Effect Level (TEL) and/or Probable Effect Level (PEL) indicating that existing concentrations of metals in these sediments were sufficiently high to cause adverse effects. However, Cr concentrations in all reservoirs evaluated was lower compared to the TEL and PEL.

An overview of research into conservation practice effects on soil and water resources in the Upper Washita Basin, Oklahoma, United States

The Fort Cobb Reservoir Experimental Watershed (FCREW) and Little Washita River Experimental Watershed (LWREW), located within the Upper Washita Basin (UWB) in Oklahoma, are part of the Agricultural Research Service (ARS) Benchmark Conservation Effects Assessment Project (CEAP)–Watershed Assessment Studies locations. The CEAP was created in 2003 by the USDA Natural Resources Conservation Service (NRCS) in partnership with USDA ARS and many other partners to quantify the environmental effects of conservation practices (CPs) and programs and to develop the science base for managing the agricultural landscape for environmental quality. The ultimate goal of this study was to present CPs that are expected to work at respective spatial scales, based on the findings of research that has been carried out in these CEAP and other watersheds within the UWB in the last 15 years. A summary of research findings indicates that the effects of CPs on soil and water resources were simulated at various spatial scales. At the large watershed scale, average annual suspended sediment yield at the 786 km² (303 mi²) FCREW outlet was reduced by 86% based on multiple CPs implemented from the 1950s to 2008 by NRCS. Specific quantified effects of studied CPs are presented herein. With the exception of red cedar (<i>Juniperus virginiana</i> L.) removal, single CPs were expected to show improvement of soil and water resources in smaller-scale watersheds. Practices that are expected to improve soil and water resources include grassland conservation from red cedar encroachment (brush control), combined streambank stabilization practices, riparian and filter strip buffer practices, and conversion of cropped area to Bermuda grass (<i>Cynodon dactylon</i> [L.] Pers.).

Reservoir Sedimentation Rates in the Little Washita River Experimental Watershed, Oklahoma: Measurement and Controlling Factors

AbstractForty‐five flood control reservoirs, authorized in the Watershed Protection and Flood Prevention Act 1954, were installed by United States Department of Agriculture (USDA) between 1969 and 1982 in the Little Washita River Experimental Watershed (LWREW), located in central Oklahoma. Over time, these reservoirs have lost sediment and flood storage capacity due to sedimentation, with rates dependent on upstream land use and climate variability. In this study, sedimentation rates for 12 reservoirs representing three major land use categories within LWREW were measured based on bathymetric surveys that used acoustic profiling system. Physiographic and climate attributes of drainage area of surveyed reservoirs were extracted from publicly available data sources including topographic maps, digital elevation models, USDA Natural Resource Conservation Service soils, and weather station databases. Correlation, principal component analysis, and stepwise regression were utilized to analyze the relationship between normalized reservoir sedimentation rates (ReSRa) and the drainage area characteristics to determine the major variables controlling sedimentation within the LWREW. Percent of drainage area with extreme slopes, saturated hydraulic conductivity, and maximum daily rainfall event recorded in spring explained most of the variability in ReSRa. It was also found that percent reduction in reservoir surface area can be used as a surrogate for estimating ReSRa. The implications of the results are discussed.

Assessing and quantifying changes in precipitation patterns using event-driven analysis

Study regionThe Little Washita River Experimental Watershed (LWREW) is located between Chickasha and Lawton in southwestern Oklahoma, US. Study focusIn this study, frequency analyses were conducted on sub-hourly precipitation event descriptors to quantify the changes in precipitation patterns commonly masked in annual analysis. Precipitation events were derived from 5-min data collected by USDA-ARS from 1961 to 2015. New hydrological insights for the regionDuring the 1962–2015 period, this region experienced successive regional long-term wet (1962–1995) and dry (1996–2015) dominated periods of more than 20 years each. During the wet period, precipitation intensity ranging from 1 to 12mm were 20% less likely to occur while event daily average precipitation and number of events increased by 10% and 11%, respectively. Also, the average daily precipitation occurred more often at lower intensities. In contrast, during the dry period, instantaneous intensity ranging from 1 to 12mm became more likely to occur (64% increase; 1996–2015) while event daily average precipitation and number of events decreased by 16% and 18%, respectively. Overall, comparisons with the baseline data (1962–2015) indicated that in the last 20 years, sub-hourly precipitation intensities have increased while daily event duration and extreme 5-min precipitation intensities larger than 24mm (precipitation intensification below extremes) have remained unchanged.

Upper washita river experimental watersheds: reservoir, groundwater, and stream flow data.

Surface and groundwater quantity and quality data are essential in many hydrologic applications and to the development of hydrologic and water quality simulation models. We describe the hydrologic data available in the Little Washita River Experimental Watershed (LWREW) of the Southern Great Plains Research Watershed (SGPRW) and Fort Cobb Reservoir Experimental Watershed (FCREW), both located in southwest Oklahoma. Specifically, we describe the flood retarding structures and corresponding stage, discharge, seepage, and consumptive use data (), stream gauges, and groundwater wells and their corresponding stream flow (; LWREW ARS 522-526 stream gauges) and groundwater level data (SGPRW groundwater levels data; LWREW groundwater data; ; ), respectively. Data collection is a collaborative effort between federal and state agencies. Stage, discharge, seepage, and consumptive use data for the Fort Cobb Reservoir are available from the Bureau of Reclamation and cover a period of 1959 to present. There are 15 stream gauges in the LWREW and six in the FCREW with varying data records. There were 479 observation wells with data in the SGPRW and 80 in the LWREW, with the latest records collected in 1992. In addition, groundwater level data are available from five real-time monitoring wells and 34 historical wells within the FCREW. These data sets have been used for several research applications. Plans for detailed groundwater data collection are underway to calibrate and validate the linked Soil and Water Assessment Tool (SWAT)-MODFLOW model. Also, plans are underway to conduct reservoir bathymetric surveys to determine the current reservoir capacity as affected by land use/land cover and overland and stream channel soil erosion.

Upper washita river experimental watersheds: meteorologic and soil climate measurement networks.

Hydrologic, watershed, water resources, and climate-related research conducted by the USDA-ARS Grazinglands Research Laboratory (GRL) are rooted in events dating back to the 1930s. In 1960, the 2927-km Southern Great Plains Research Watershed (SGPRW) was established to study the effectiveness of USDA flood control and soil erosion prevention programs. The size of the SGPRW was scaled back in 1978, leaving only the 610-km Little Washita River Experimental Watershed (LWREW) to be used as an outdoor hydrologic research laboratory. Since 1978, the number of measurement sites and types of instruments used to collect meteorologic and soil climate data have changed on the LWREW. Moreover, a second research watershed, the 786-km Fort Cobb Reservoir Experimental Watershed (FCREW), was added in 2004 to the GRL's outdoor research laboratories to further study the effects of agricultural conservation practices on selected environmental endpoints. We describe the SGPREW, FCREW, and LWREW and the meteorologic measurement network (historic and present) deployed on them, provide descriptions of measurements, including information on accuracy and calibration, quality assurance measures (where known), and data archiving of the present network, give examples of data products and applications, and provide information for the public and research communities regarding access and availability of both the historic and recent data from these watersheds.

Upper washita river experimental watersheds: multiyear stability of soil water content profiles.

Scaling in situ soil water content time series data to a large spatial domain is a key element of watershed environmental monitoring and modeling. The primary method of estimating and monitoring large-scale soil water content distributions is via in situ networks. It is critical to establish the stability of in situ networks when deploying them to study hydrologic systems. Two watersheds in Oklahoma, the Little Washita River Experimental Watershed (LWREW) and the Fort Cobb Reservoir Experimental Watershed (FCREW), are two prime examples of well-equipped research watersheds that provide long-term measurements of atmospheric and soil water content from in situ networks. The soil water content measurement network on the LWREW has been in operation since 2002, with 20 stations available for investigating soil water dynamics at the watershed scale. Temporal stability analysis of the network is complicated by the changing configuration of the network, but it is possible to determine a singular long-term average for the network. The FCREW consists of 15 soil water content stations and began operation in 2007, providing detailed information across a mixed agricultural domain and was determined to be stable and representative of the region. This study reinforces the applicability of temporal stability analysis to very long time scales, which are now becoming available for soil moisture monitoring. Each of these networks is temporally stable with respect to soil water content at each depth on a spatial basis. The LWREW has a persistent pattern through the root zone profile, but the FCREW does not, which requires further investigation.

Upper washita river experimental watersheds: physiography data.

Physiographic data such as digital elevation models (DEMs), soils, geology, stream channel network characteristics, channel stability, and land use data are essential for understanding the complex hydrologic cycle and chemical transport processes of any given study area. We describe the physiographic data available in the Little Washita River Experimental Watershed (LWREW) and Fort Cobb Reservoir Experimental Watershed (FCREW) in Oklahoma. Specifically, we describe (i) available raw and post-processed DEM products (), (ii) available soils data ( and ) and associated error analysis based on limited measured data, (iii) geologic formations in the LWREW and FCREW ( and ), and (iv) available rapid geomorphic assessment measurements () and their uses. Data collection is a collaborative effort among USGS, NRCS, and ARS. These data sets have been used for several research applications by USDA-ARS scientists and researchers from other institutions and agencies. Plans for detailed geomorphic assessment of stream channel networks in the FCREW are underway in collaboration with Oklahoma State University in Stillwater. The collected data will enable updating of the channel stability stage condition since there have been several major rainfall events in the watershed since the last geomorphic assessment.

Upper washita river experimental watersheds: nutrient water quality data.

Climate variability, changing land use and management, and dynamic policy environments are the main reasons why long-term research is needed to understand and predict possible water quality outcomes to alternative future scenarios. Long-term water quality data sets are needed to address these water issues. Such data sets were acquired by the USDA-ARS in three watersheds in Oklahoma: the Southern Great Plains Research Watershed (SGPRW), the Little Washita River Experimental Watershed (LWREW), and the Fort Cobb Reservoir Experimental Watershed (FCREW). We provide: (i) a description of these water quality data sets, (ii) the sample collection and processing procedures used and an assessment of the data quality, (iii) summary analyses of the variability in each data set, and (iv) details about how to access these data sets. Water quality data collection in the SGPRW began in the 1960s and continued through 1978, while that in the LWREW covered the 1960s to 1990 period. Data collection began in the FCREW in 2004 and continues through the present. The data were collected from streams, unit source watersheds, groundwater wells, and reservoirs. The water quality data described for a given site are generally complete for a given period of record; however, not all sites were monitored continuously and were not necessarily analyzed for the same water quality parameters. These data sets are expected to improve modeling and assessments of conservation practices in relation to climate variability, land use changes, and other environmental factors and may be useful in developing strategies to mitigate these environmental impacts.

The Impact of Asynchronicity on Event‐Flow Estimation in Basin‐Scale Hydrologic Model Calibration1

Abstract: The calibration of basin‐scale hydrologic models consists of adjusting parameters such that simulated values closely match observed values. However, due to inevitable inaccuracies in models and model inputs, simulated response hydrographs for multiyear calibrations will not be perfectly synchronized with observed response hydrographs at the daily time step. An analytically derived formula suggests that when timing errors are significant, traditional calibration approaches may generally underestimate the total event‐flow volume. An event‐adaptive time series is developed and incorporated into the Nash‐Sutcliffe Efficiency objective function to diagnose the potential impact of event‐flow synchronization errors. Test sites are the 50 km2 Subwatershed I of the Little River Experimental Watershed (LREWswI) in southeastern Georgia, and the 610 km2 Little Washita River Experimental Watershed (LWREW) in southwestern Oklahoma, with the Soil and Water Assessment Tool used as the hydrologic model. Results suggest that simulated surface runoff generation is 55% less for LREWswI when the daily time series is used compared with when the event‐adaptive technique is used. Event‐flow generation may also be underestimated for LWREW, but to a lesser extent than it may be for LREWswI, due to a larger portion of the event flow being lateral flow.

Surface and profile soil moisture spatio-temporal analysis during an excessive rainfall period in the Southern Great Plains, USA

In this work we analyze the temporal stability of soil moisture at the field and watershed scales in the Little Washita River Experimental Watershed (LWREW), as part of the remote sensing Cloud and Land Surface Interaction Campaign (CLASIC07) during June 2007 in south-central Oklahoma. Temporal stability of surface and profile soil moisture data were investigated for 20 LWREW soil moisture measurement stations. In addition, daily surface and profile soil moisture measurements were obtained in four 800 m by 800 m fields (remote sensing footprint), including two rangeland sites and two winter wheat fields. The work aimed to analyze the temporal stability of soil moisture at the watershed and field scale and to identify stations within the watershed, as well as locations within each field, that were representative of the mean areal soil moisture content. We also determined the relationship between sites found to be temporally stable for surface soil moisture versus those determined stable for average profile soil moisture content. For the unusually wet experimental period, results at the watershed scale show that LWREW stations 133 and 134 provided stable underestimates, while stations 132 and 154 provided stable overestimates of the watershed mean at all depths. In addition, station 136 had very high non-zero temporal stability at the 25 cm and 45 cm depths indicating that it could be used as representative watershed site provided a constant offset value is used to acquire a watershed mean soil water content value. In general, the deeper depths exhibited higher soil moisture spatial variability, as indicated by the higher standard deviations. At the field scale, measured average profile soil moisture was higher in the winter wheat fields than the rangeland fields with the majority of the winter wheat depth intervals having high non-zero temporal stability. Field scale temporal stability analysis revealed that 4 of the 16 sampling sites in the rangeland fields and 3 of the 16 sampling sites in the winter wheat fields either under or overestimated the field means in the 0–5 and 0–60 cm depth intervals. Field sites considered temporally stable for the surface soil moisture were not stable for the profile soil moisture, except for the LW45 field where two sites were stable at both the surface and profile soil moisture. This finding is significant in terms of soil moisture ground-truth sampling for calibrating and validating airborne remotely sensed soil moisture products under extremely wet conditions. In addition, identification of temporally stable sites at the watershed and field scales in the LWREW provide insight in determining future measurement station locations and field scale ground sampling protocol, as well as providing data sets for hydrologic modeling.

Temporal stability of soil moisture profile

The temporal stability of soil moisture profile across the 610 km 2 Little Washita River Experimental Watershed (LWREW), located in southwestern Oklahoma, is investigated. Experimental data were acquired by time-domain reflectometry (TDR) probes. TDR data were routinely collected at eight locations during the months of June and July in 1997 and in July 2003, coincident with large-scale hydrological remote sensing experiments. Analyses were performed to determine if a subset of the TDR sites could be used to represent watershed averages (i.e. sensor network averages) of soil water content at various levels in the soil profile, as well as in the total profile. The results show that two of the eight TDR sites were temporally stable. One site consistently underestimated and the other consistently overestimated watershed average soil water content at all levels in the soil profile. Because the offset between these under- and over-estimates and the watershed mean are known, these sites can be used to determine the watershed mean values of soil water content at all levels in the profile, as well as to provide ranges of soil water content within the watershed. Identification of these temporally stable sites within the LWERW will assist in the validation of coarse spatial resolution surface soil moisture products derived from remote sensing experiments, as well as providing data sets for watershed hydrologic modeling of subsurface soil water contents.

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.

HYDROLOGIC SIMULATION ON AGRICULTURAL WATERSHEDS: CHOOSING BETWEEN TWO MODELS

Strengths and limitations of hydrologic simulation models are used as criteria for selecting a particular modelfor a given water resources application. The performance of the Soil and Water Assessment Tool (SWAT) and the HydrologicSimulation Program-Fortran (HSPF) continuous simulation models was compared on eight nested agricultural watershedswithin the Little Washita River Experimental Watershed (LWREW) and two agricultural watersheds adjacent to the LWREWwithin the Washita River Basin in southwestern Oklahoma. Two subwatersheds within the LWREW were first used to calibrateparameters in both models for a wetter than average period of record. Both models were then applied to six othersubwatersheds within the LWREW and the two adjacent watersheds, under varying climatic conditions. Three quantitativeand two qualitative evaluation criteria were used to assess streamflow simulated by SWAT and HSPF: computation of(1) deviation of streamflow volume, (2) coefficient of efficiency, and (3) prediction efficiency and visual inspection of(4) hydrographs and (5) flow duration curves. A comparison of model performance showed that while HSPF performed betteron the watersheds used for calibration, SWAT gave better results on the validation watersheds. On one of the validationsubwatersheds adjacent to the LWREW, values of deviation of streamflow volume were -38.7%, -13.3%, and -1.3% for SWATand -64.3%, -81.1%, and -8.2% for HSPF under much dryer than average, dryer than average, and near averageclimatic conditions, respectively. Differences in model performance were mainly attributed to the runoff productionmechanism in the two models. Results of this study showed that SWAT exhibited an element of robustness in that it gave moreconsistent results than HSPF in estimating streamflow for agricultural watersheds under various climatic conditions. SWATmay therefore be better suited for investigating the long-term impacts of climate variability on surface-water resources.

Time Domain Reflectometry Field Calibration in the Little Washita River Experimental Watershed

Accurate measurement of profile soil water content is essential to many areas of environmental and agricultural research. In this study five methods were evaluated for determining volumetric profile soil water content from time domain reflectometry (TDR) data at nine locations within the Little Washita River Experimental Watershed (LWREW) in south central Oklahoma. Soil compositions for the sites ranged between 24.6 to 86.4% for sand and 5.2 to 29.2% for clay. Comparisons were made between gravimetric soil sample data and soil water content as determined by the TDR factory instrument calibration, two methods of site-specific calibration, a regional calibration technique, and an empirically derived universal approach. Method 1 is the factory calibration, which uses average values for model coefficients that were derived from extensive laboratory work and theoretical analysis. Method 2 fits a site-specific linear regression of TDR time delay on measured soil-core water content. Method 3 uses the factory calibration equation and site-specific values for the ratio of TDR time delay in dry soil, to that in air (Ts/Ta). In Method 4, a regional linear regression equation was developed from an analysis combining data from all study sites. Method 5 applies a universal equation based on the linear relationship between soil water content and the apparent dielectric constant of soil (Ka) measured by TDR. Statistical analysis of the data showed that of the five methods, only the mean root mean square error (RMSE) value for Method 2 was significantly different from all other methods (α = 0.05). Method 2 also had the smallest standard deviation and standard error, and the narrowest range of RMSE values. All field calibration methods show that it is necessary to include very low water content data in determining absolute water content. When compared with the factory calibration, all other methods improved the measurement of soil water content, with Method 2 providing the most accurate results at the site-specific level of analysis.

Time Domain Reflectometry Field Calibration in the Little Washita River Experimental Watershed

Accurate measurement of profile soil water content is essential to many areas of environmental and agricultural research. In this study five methods were evaluated for determining volumetric profile soil water content from time domain reflectometry (TDR) data at nine locations within the Little Washita River Experimental Watershed (LWREW) in south central Oklahoma. Soil compositions for the sites ranged between 24.6 to 86.4% for sand and 5.2 to 29.2% for clay. Comparisons were made between gravimetric soil sample data and soil water content as determined by the TDR factory instrument calibration, two methods of site‐specific calibration, a regional calibration technique, and an empirically derived universal approach. Method 1 is the factory calibration, which uses average values for model coefficients that were derived from extensive laboratory work and theoretical analysis. Method 2 fits a site‐specific linear regression of TDR time delay on measured soil‐core water content. Method 3 uses the factory calibration equation and site‐specific values for the ratio of TDR time delay in dry soil, to that in air (Ts/Ta). In Method 4, a regional linear regression equation was developed from an analysis combining data from all study sites. Method 5 applies a universal equation based on the linear relationship between soil water content and the apparent dielectric constant of soil (Ka) measured by TDR. Statistical analysis of the data showed that of the five methods, only the mean root mean square error (RMSE) value for Method 2 was significantly different from all other methods (α = 0.05). Method 2 also had the smallest standard deviation and standard error, and the narrowest range of RMSE values. All field calibration methods show that it is necessary to include very low water content data in determining absolute water content. When compared with the factory calibration, all other methods improved the measurement of soil water content, with Method 2 providing the most accurate results at the site‐specific level of analysis.