Evaluating the Role of Evapotranspiration in the Hydrology of a Bioinflltration Basin Using a Weighing Lysimeter

摘要

Bioinflltration basins require substantial land area in order to reduce peak outflows and improve the water quality of stormwater runoff. An increased understanding of the water budgets occurring within these basins could result in more efficient land usage. For example, the role of water losses through groundwater recharge, and specifically evapotranspiration (ET), are not well understood. However, research on the entire water budget may yield design standards resulting in substantial volume reduction in bioinflltration basins when the contribution of ET is viewed through an appropriate time horizon.In order to measure the ET and groundwater recharge occurring in a bioinflltration basin, a weighing lysimeter was designed and constructed. Storms were simulated representing varying field conditions. These simulations mimicked two and a half hour storm events of 13, 19, and 25 mm producing runoff occurring from both 5:1 and 10:1 impervious area to lysimeter area loading ratios. The simulations were conducted during the morning and evening and in different seasons. Results indicate that the ET measured 24 hours after the storm simulation was found to range from 2.6 to 31.4 mm of water. The measured ET was found to be strongly correlated (R~2 = 0.63) to the climatological parameters that govern the Penman-Monteith equation. The measured ET was compared to the Penman-Monteith reference ETo and a mean crop coefficient (K_c) of 1.85 was determined for the summer months. The measured ET was also found to be dependent on the soil saturation of the lysimeter prior to the storm simulation. A soil-water characteristic curve was developed for the soil in the lysimeter. It was determined that the greater the soil suction throughout the storm simulation, the more water that was available for ET, and ET increased relative to groundwater recharge.