ESTIMATING AGRICULTURAL BENEFITS FROM DRAINAGE OVER A RELATIVELY LEVEL TERRAIN

Many regions of the world incur flooding and a high water table over a relatively large, level land area. Methodology was developed and programmed for analysis of soil drainage and flood protection benefits in such regions. Estimates of yield loss were elicited from South Texas farmers for floods occurring on average once every year (i.e. 100% flood frequency or probability of occurrence), once every 2 years ( 50% flood frequency), once every 5 years (20% flood frequency), once every 10 years (10% flood frequency), and once every 25 years (4% flood frequency). The Agricultural Benefits Estimator model, ABE, was applied to an analysis of subsurface drainage improvements and flood protection for 0.25 million ha in the South Texas study area. Results indicate substantial project benefits from both lowering the water table and providing alternative levels of reduced flooding. For the case study, the present value of benefits to agriculture from flood protection were estimated at $83.1 million for protection from flooding events with a 50% flood frequency. Estimated benefits were $88.2 million for flood protection through the 20% flood frequency, and benefits increased by another $2.7 million ($90.9 million total) for flood protection through the 10% flood frequency.