The ability of a watershed model to mimic specified watershed processes is assessed through the calibration and validation process. The Soil and Water Assessment Tool (SWAT) watershed model was implemented in the Beaver Reservoir Watershed of Northwest Arkansas. The objectives were to: (1) provide detailed information on calibrating and applying a multisite and multivariable SWAT model; (2) conduct sensitivity analysis; and (3) perform calibration and validation at three different sites for flow, sediment, total phosphorus (TP), and nitrate‐nitrogen (NO3‐N) plus nitrite‐nitrogen (NO2‐N). Relative sensitivity analysis was conducted to identify parameters that most influenced predicted flow, sediment, and nutrient model outputs. A multi objective function was defined that consisted of optimizing three statistics: percent relative error (RE), Nash‐Sutcliffe Coefficient (RNS2), and coefficient of determination (R2). This function was used to successfully calibrate and validate a SWAT model of Beaver Reservoir Watershed at multi‐sites while considering multivariables. Calibration and validation of the model is a key factor in reducing uncertainty and increasing user confidence in its predictive abilities, which makes the application of the model effective. Information on calibration and validation of multisite, multivariable SWAT models has been provided to assist watershed modelers in developing their models to achieve watershed management goals.

Chemigation is a process by which an irrigation system is used for transport and delivery of an agrochemical, generally fertilizers or pesticides, to a crop. Often times, the irrigation system used in chemigation is drip irrigation. The purpose of this report is to provide some helpful tips for papaya growers interested in chemigation. This document is ABE 360, one of a series of the Department of Agricultural and Biological Engineering, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, Universtiy of Florida. First printing: August 2005.

In situ assessments of chemical toxicity in streams may be accomplished using natural periphytic communities when allowed to colonize an artificial substrate. The proliferation of Triclosan (TCS) in consumer products has resulted in its presence in wastewater influent, effluent, and subsequently in streams. In this study, the two objectives were: 1) assess the utility of a passive−diffusion periphytometer in toxicity tests, and 2) evaluate the growth−inhibiting effects of TCS on periphytic algae at the White River, Northwest Arkansas. The periphytometer was deployed for one week with seven replicates of nine treatments, including control (deionized H 2

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The Buffalo National River (BNR) is a relatively unpolluted, free−flowing river with riffle−pool geomorphology, located in north−central Arkansas. The specific objectives of this study were to: (1) evaluate differences between physicochemical properties and concentrations in water quality samples representing base flow and surface runoff conditions, (2) determine trends in physicochemical properties and concentrations using three datasets (all data, data representing base flow conditions, and data representing surface runoff conditions), and (3) compare flow−weighted constituent concentrations and yields at the BNR to relatively undisturbed catchments and a relatively developed catchment. Water quality trends were evaluated (a = 0.1) using constituent data from 1991 through 2001 and using subsets of these data representing water quality samples collected during either base flow or surface runoff conditions. Trends were assessed by (1) appropriately transforming water quality data and daily discharge, (2) flow−weighting water quality data using a smoothing technique, and (3) evaluating residuals from smoothing versus time for trends. Trend analyses suggested that only nitrogen, sediment, and E. coli concentrations increased from 1991 through 2001 in the BNR, particularly during surface runoff conditions. Most temporal changes in constituents occurred during surface runoff conditions, and these changes were not necessarily reflected during base flow conditions. Flow−weighted nutrient concentrations and yields were greater at the BNR compared to median values for relatively undeveloped basins across the U.S. Nutrient concentrations and yields at the BNR were only slightly greater than or equal to the values representing the 75th percentile of reference streams. However, nutrient concentrations and yields at the BNR were less than at relatively developed basins within the same ecoregion. By evaluating base flow and surface runoff water quality samples separately for trends, we gained additional insight into the particular flow conditions exhibiting significant trends. Identification of flow conditions associated with trends aids in determining constituent sources and hence appropriate constituent abatement.

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Hydrologic Response Unit (HRU) is a unit formed of hydrological analysis based on geology and soil type, slope, and land cover. This paper discussed the spatial pattern of Hydrologic Response Unit (HRU) in 1997-2009 and its impact on flow Ci Rasea watershed temporally. In this study, SWAT (Soil and Water Assessment Tool) model, based on land cover changed, was used to get HRU and flow in spatially and temporally. This method used Landsat TM 1997, 2003 and 2009 data for land cover and daily rainfall 1997-2009 for flow modeling. The results showed the spatial pattern of HRU in temporally was affected by landcover based on the changing of HRU. The majority of HRU spatial pattern at Ci Rasea watershed were clustered. During 1997-2009, accumulated surface runoff and the changing of flow discharge were affected by changes of HRU spatial pattern. The biggest accumulated surface runoff in Ci Rasea watershed influenced by HRU of agricultural cropland in area of clay soil type with slope slightly obliquely. While the smallest accumulated surface runoff in Ci Rasea watershed influenced by HRU of paddy field in the area of sandy loam soil type with a gentle slope. The changes of HRU agriculture cropland become HRU mixed cropland in area clay soil type with slope at a slight angle and HRU agriculture cropland become HRU paddy field in area, sandy loam soil type with a gentle slope could be decreasing the accumulation of surface runoff in Ci Rasea watershed.