WATERSHED MODELING WITH IRRIGATION IMPACTS FOR URBAN AND AGRICULTURAL APPLICATIONS USING HSPF

Capabilities of watershed models have continued to evolve over the past decade, with advances in computing power and scientific knowledge, to greatly improve the ability to represent complex watersheds with increasing detail both spatially and temporally. In many watersheds, irrigation is a major component of the overall water balance with major impacts on the hydrologic regime. This is clearly evident in highly intensive agricultural areas, and especially for watersheds in semi-arid regions. Moreover, urban development, in semi-arid regions, is often accompanied by extensive landscape watering which can have a confounding impact on the hydrologic regime, in conjunction with stormwater increases from urbanization, and subsequent planning and evaluation of mitigation practices. Yet only recently have capabilities been developed to specifically accommodate the need to consider irrigation applications in watershed modeling studies.Over the past five years, the U. S. EPA HSPF watershed model has been applied to numerous watersheds where irrigation applications have been critical to the accurate representation of the hydrologic regime and overall water balance. These applications have included both urban and agricultural watersheds, and in both humid and semi-arid environments. This paper reports on a variety of ways in which irrigation has been included within recent HSPF applications across the country, from Florida to Texas to California, to include both urban landscape watering and extensive agricultural applications in semi-arid regions, using water derived from both surface water and groundwater sources. The HSPF irrigation module capabilities are described and case study examples are presented to demonstrate irrigation impacts under different climatic and land use conditions, and irrigation and agronomic practices.