A decision support framework (DSF) to guide watershed management planning in St. Lucia was developed. The DSF, supported by three components, integrated physiographic criteria in spatially defining sustainable land management regimes, crop suitability based on agro-ecologic zoning criteria, and water quality modelling tools. / In the first component, a methodology for agricultural and forestry land management zoning based on decision-rule frameworks was developed, employing GIS-based spatial multiple-criteria integration techniques. Land capability, recommended land management regimes, crop suitability and broad agricultural/forestry land utilization type zones were derived for the country. Sixteen broad agricultural and forestry land utilization types (LUTs) based on FAO agro-ecologic zoning guidelines were spatially defined over the island. These LUT zones represent relative suitability for rain-fed annual and perennial crop production, grazing and forestry. / In the second component, field research to quantify rainfall, runoff and erosion from two small watersheds under contrasting land management regimes was undertaken. Over the study period the erosion rate from an intensively cultivated, degraded agricultural watershed was 20 times that of a completely forested watershed. SCS curve numbers were evaluated for both watersheds based on rainfall-runoff relationships. / The third component demonstrated the application of a distributed-parameter hydrologic/water quality model, AnnAGNPS, in land management scenario evaluation, in terms of runoff and soil erosion. Data from the second component were used to calibrate and validate the model in simulation of daily runoff and erosion losses from the two watersheds over the study period. The model generally performed better in runoff simulation for the agricultural watershed compared to the forested watershed. Average annual erosion rates under current land management regimes were estimated at 73.3 and 7.2 t/ha for the agricultural and forested watersheds respectively. The model was applied to simulate runoff and erosion losses from the agricultural watershed under alternative sustainable land management regimes derived in the first component. Simulated average annual erosion losses were reduced to 9.2 t/ha. / This study demonstrated the application of efficient and powerful computer-based tools in the development of a decision support framework for watershed management planning for small islands.

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A method for estimating long-term average annual soil loss under different land management scenarios from the Marquis and Soufriere watersheds on St. Lucia is presented. The Revised Universal Soil Loss Equation (RUSLE) was used, and a GIS was employed to generate the required input parameters. Model execution and results were also generated within the GIS. Modelling soil loss for the different land management scenarios was based upon a land capability classification and associated conservation treatments. Soil losses under current agricultural land-use patterns were analyzed and compared to potential soil losses under conservation treatments following the criteria specified in the land capability classification. The model predicted substantial declines in soil loss where conservation treatments were assigned, as compared to soil loss under current land-use patterns. It was found that predicted soil losses from the Soufriere watershed were four times that predicted for the Marquis watershed for all the land management scenarios modelled. Of the input parameters in the model, slope steepness was most highly correlated to predicted soil loss. It is anticipated that the findings of this study will be used in the development of a decision support system for agricultural and forestry land planning on St. Lucia.

No description available.