Critical Source Areas Research Articles

Identification of critical sediment source areas at regional level

In order to identify critical sediment sources in large catchments, using easily available terrain information at regional scale, a methodology has been developed to obtain a qualitative assessment necessary for further studies. The main objective of the model is to use basic terrain data related to the erosive processes which contribute to the production, transport and accumulation of sediments through the main water paths in the watershed. The model is based on the selection of homogeneous zones regarding drainage density and lithology, achieved by joining the spatial basic units by a rating system. The values of drainage density are rated according to an erosion class (Bucko & Mazurova, 1958). The lithology is rated by erosion indexes, adapted from FAO (1977). The combination and reclassification of the results brings about five qualitative classes of sediment emission risk. This methodology has been tested an validated for the watershed of the Joaquín Costa reservoir (NE Spain), with a surface of 1500 km 2. The mapping scale was 1:100.000 and the model was implemented through a vector GIS (Arc/Info). The prediction was checked by means of photo-interpretation and field work, which gave a accuracy of 78.5%. The proposed methodology has been proved useful as an initial approach for erosion assessment and soil conservation planning at the regional level, and also to select priority areas where further analyses can be developed.

Urban stormwater toxic pollutants: assessment, sources, and treatability

This paper summarizes an investigation to characterize and treat selected storm water contaminants that are listed as toxic pollutants (termed toxicants in this paper) in the Clean Water Act, Section 307 (Arbuckle et al., 1991). The first project phase investigated typical toxicant concentrations in storm water, the origins of these toxicants, and storm and land‐use factors that influenced these toxicant concentrations. Of the 87 storm water source area samples analyzed, 9% were considered extremely toxic (using the Microtox® toxicity‐screening procedure). Moderate toxicity was exhibited in 32% of the samples, whereas 59% of the samples had no evidence of toxicity. Only a small fraction of the organic toxicants analyzed were frequently detected, with 1,3‐dichlorobenzene and fluoranthene the most commonly detected organics investigated (present in 23% of the samples). Vehicle service and parking area runoff samples had many of the highest observed concentrations of organic toxicants. All metallic toxicants analyzed were commonly found in all samples analyzed. The second project phase investigated the control of storm water toxicants using a variety of bench‐scale conventional treatment processes. Toxicity changes were monitored using the Microtox® bioassay test. The most beneficial treatment tests included settling for at least 24 hours (up to 90% reductions), screening and filtering through at least 40‐μm screens (up to 70% reductions), and aeration and/or photodegradation for at least 24 hours (up to 80% reductions). Because many samples exhibited uneven toxicity reductions for the different treatment tests, a treatment train approach was selected for the current project phase. This current phase includes testing of a prototype treatment device that would be useful for controlling runoff from critical source areas (e.g., automobile service facilities).

Sources of Pollutants in Wisconsin Stormwater

Rainfall runoff samples were collected from streets, parking lots, roofs, driveways, and lawns. These five source areas are located in residential, commercial, and industrial land uses in Madison, Wisconsin. Solids, phosphorus, and heavy metals loads were determined for all the source areas using measured concentrations and runoff volumes estimated by the Source Load and Management Model. Source areas with relatively large contaminant loads were identified as critical source areas for each land use. Streets are critical source areas for most contaminants in all the land uses. Parking lots are critical in the commercial and industrial land uses. Lawns and driveways contribute large phosphorus loads in the residential land use. Roofs produce significant zinc loads in the commercial and industrial land uses. Identification of critical source areas could reduce the amount of area needing best-management practices in two areas of Madison, Wisconsin. Targeting best-management practices to 14% of the residential area and 40% of the industrial area could significantly reduce contaminant loads by up to 75%.

Runoff and erosion from a small semiarid catchment, Baringo district, Kenya

Runoff and sediment yield data are presented from a 0.3-km 2, highly erodible semiarid catchment in the Baringo District, Rift Valley Province, Kenya. Field observations indicated Hortonian overland flow production on all major lithologic units with rainfall intensities of 6–9mm hr −1. High runoff coefficients, with a mean value of 46 per cent for events studied in 1986, were attributed to minimal vegetation cover and the mechanical and chemical clay dispersion of sodium-rich smectite surface soils. Suspended sediment yield for 1986 was approximately 7000t km −2. A minimal bedload estimate for the same period was 310t km −2. Thus, the overall sediment output was in the order of 7300t km −2yr −1, representing an overall basin lowering of approximately 4.0mmyr −1 (assuming a bulk density of 1–5mgm −3). Catchment sediment output data are placed within a sediment budget framework in order to identify critical source areas of erosion. Remobilization of stored colluvium was found to be the major source of finegrained sediment output from the catchment. Identification of colluvial areas as the major source area for sediment production is critical from an applied perspective. Management of these areas is necessary to reduce or control high runoff rates and soil erosion. Two land management schemes are discussed, the first focusing on increasing infiltration in colluvial areas through surface rock mulches and the establishment of a perennial grass cover ( Cenchrus ciliaris). An alternative plan would be to apply rainwater-harvesting techniques in the colluvial zone. This would involve water retention on the hillslopes which would increase water availability for plants, decrease Hortonian overland flow, and thus decrease the loss of soil and soil-associated nutrients.

A GIS method to aid in non-point source critical area analysis

Abstract The use of remote sensing techniques, image processing, computer mapping and overlays to make inventories of land use and to improve land and water management has increasing potential. Advantages of these techniques include greater geometric resolution and potential time and money savings. The increasing capabilities of personal computers and workstations (hardware and software) and the greater availability of databases have simplified the application of these techniques. In this application, a geographical information system (GIS) was used to facilitate the identification of critical non-point source areas of pollution by sediment-related nutrients. This critical source area information might then be used to aid in the development of non-point source control strategies or for monitoring programme design. This study shows the potential of using GIS in selecting critical source areas for sediment-related water quality problems and land resource protection.