DETERMINATION IN-SITU RUNOFF HARVESTING (IRH) POTENTIAL OF WATERSHEDS IN ARID AND SEMI-ARID AREAS

Rainwater harvesting techniques are ancient practices that have been used for many years by different countries and civilizations. Runoff water harvesting is a promising technique to collect water and store it effectively in surrounding plant or crop areas. With global warming and climate change, water availability and accessibility are becoming even more critical, particularly in arid and semi-arid areas of the world. Annual rainfall is either scarce or insufficient to support farming practices in many areas. Thus, it is necessary to capture, store, and utilize water when it is sufficient for the growing season of different crops. In this sense, it is also important to evaluate differences in watersheds in terms of determining where the water flows (runoff areas) and where it can be collected for in situ use (run on areas). Based on land use, surface types, land cover, and soil group parameters, the amount of water changes within a watershed so it is crucial to determine and combine those factors. The aim of this study is to develop methodologies for determining the runoff harvesting potential of watersheds in arid and semi-arid areas. Specifically, to: 1) Identify potential areas for in-situ runoff harvesting (IRH)within watersheds; and 2) Estimate surface runoff volumes in areas as identified. The pilot study area for this study is Winters Wash Watershed, which is a sub-watershed of Centennial Wash located in Arizona (HUC number: 15070104). This watershed serves as a proxy for arid and semi-arid areas and was selected because it has sufficient data for the planned analysis. Based on the analysis, 17,615 ha (25% of the watershed area) were classified as being suitable or highly suitable as runoff sources, while 14,092 ha (20% of the watershed area) were better suited as run on collection areas. Total collectible runoff was determined on an average annual basis. Finally, recommendations on suitable water harvesting techniques were made based on land use, soil, surface structure, and slope in the watershed. The results will provide a methodology for the decision-making process for identifying both run on and runoff areas and examples of real practices that could be used in places that are arid and semi-arid.