You are in charge of estimating the runoff for generated over a 40-acre basin due to a 100-year 30-min design storm that produced 2.71 inches over 30 minutes, assuming uniform precipitation over the 30 minutes. The soils in the watershed are 33% clay, 59% silt and 8% sand. Prior to the storm, the soil had an effective saturation of 25% with an initial infiltration capacity of 17.8 cm/hr. From previous events, it was determined that the soil has a time constant k of 3.45 hr-1, and an ultimate infiltration capacity of 1.7 cm/hr. a. Derive an equation for time to ponding using the Horton model
b. Estimate the time to ponding (minutes) for the watershed basin using the Horton model and the Green-Ampt model. Discuss why these values are the same/different.
c. Use the Horton and Green-Ampt model to estimate the total infiltration (cm) during the storm
d. What is the runoff (acre-ft) using the Horton model and Green-Ampt model?