| Title: | Modeling flow and pollutant transport in a karst watershed with SWAT |
| Authors: | Baffaut, C. and V.W. Benson |
| Year: | 2009 |
| Journal: | Transactions of the ASABE |
| Volume (Issue): | 52(2) |
| Pages: | 469-479 |
| Article ID: | |
| DOI: | 10.13031/2013.26840 |
| URL (non-DOI journals): | |
| Model: | SWAT (modified) |
| Broad Application Category: | hydrologic and pollutant |
| Primary Application Category: | karst geological effects |
| Secondary Application Category: | pathogen fate and transport |
| Watershed Description: | The James River basin is a large watershed (3,600 km^2) in southwest Missouri, USDA, characterized by losing streams, springs, and sinkholes. Perennial streams are fed by surface and groundwater flow. The watershed is generally hilly and presents rock outcrops in some areas. Slopes are on average between 5% and 8%, with flatter areas in the north (2% slope) and steeper slopes adjacent to the streams (11% to 15%). The dissolution of limestone and dolomite resulted in karst topography. That topography resulted in many springs, sinkholes, and losing streams throughout the basin. Almost all the streams are losing streams. Half of the river basin is covered by soils characterized by a very deep soil profile with high permeability (60 mm/h) and high rock fractions (20% to 80%). Another 20% of the watershed is covered by soils with a shallow restrictive layer that reduces permeability and increases the potential for surface runoff and lateral flow. Rock fractions are again very high. Deep and well drained soils are found in the flood plain. The watershed's predominant land uses include grassland (pasture and hay fields), urban areas, and forests. |
| Calibration Summary: | PBIAS on total flow at 4 gauges: Calibration:4% to 20%
PBIAS on surface runoff: Calibration: -2% to 11%
Daily NSE flow: Calibration: 0.33 to 0.56
P loads PBIAS: Calibration: 7% to -101% |
| Validation Summary: | PBIAS on total flow at 4 gauges: Validation: -2% to -21%
PBIAS on surface runoff: Validation: 2% to -9%
Daily NSE flow: Validation: 0.24 to 0.56
P loads PBIAS: Validation: -52% to -538% |
| General Comments: | Modification to the SWAT code improved the surface runoff/base flow separation in the upper parts of the watershed. |
| Abstract: | Karst hydrology is characterized by multiple springs, sinkholes, and losing streams resulting from acidic water percolating through limestone. These features provide direct connections between surface water and groundwater and increase the risk of groundwater, springs and stream contamination. Anthropogenic activities (agriculture, tourism, urban and residential areas) accentuate the contamination potentials. The objectives of this paper are to present a modification of the Soil and Water Assessment Tool (version 2005) that allows faster percolation through the soil substrate and recharge of the aquifer. This addition was necessary to simulate quick movement of water through vertical conduits that characterize karst topography. The model was calibrated for the James River Basin, a large watershed (3,600 km^2) in Southwest Missouri. Losing streams were simulated by specifying high soil conductivities in the channels, and sinkholes were simulated as ponds with a high hydraulic conductivity at the bottom. Results indicated that the changes improved the partition of stream flow between surface and return flow. Water quality results indicated that the SWAT model can be used to simulate the frequency of occurrence of pollutant concentrations and daily loads. This case study highlights the possibilities and limitations in modeling flow and water pollutant movement in a karst watershed. |
| Language: | English |
| Keywords: | Watershed, modeling, hydrology, SWAT, karst, model performance, groundwater, recharge, phosphorus, fecal coliform |