Performance Evaluation of Commonly Used Infiltration Models

Infiltration is the process of water entry into a soil from rainfall, snowmelt or irrigation. Infiltration rate is the rate at which the water actually infiltrates through the soil during a storm. It is a measure of how fast water enters the soil, typically expressed in inches per hour (in/h) or millimeters per hour (mm/h). Soil infiltration rate is a critical parameter in the design and evaluation of stormwater control facilities. Infiltration equations are needed to design and optimize stormwater infiltration practices. The aim of this research was to evaluate selected infiltration models (Horton's, Modified Kostiakov, and Green and Ampt) used to estimate final soil infiltration rate. Parameters of the models will be estimated. The goodness of fit of the three equations for infiltration will be tested using the Root Mean Squared Error (RMSE) to compare values of predicted infiltration rate evaluated at each time interval, to determine how closely each equation predicts the measured infiltration.

During these studies, surface double-ring infiltration tests and large borehole infiltration measurements were conducted in the field to determine the surface infiltration characteristics and the subsurface infiltration characteristics (located at the depths at the bottom of the bioinfiltration devices). The effects of different compaction levels on the infiltration rates through the soil media were also examined during controlled laboratory column tests. For the double-ring infiltration tests, the measurements were taken every 5 minutes at the beginning of the test and less frequently as the test progressed until the rate of infiltration was considered constant. The tests lasted one to two hours in each location. Infiltration model parameters will be compared with measured infiltration rates from double ring infiltrometer tests.

Keyword: Stormwater, Infiltration, Double-ring infiltration, Borehole infiltration, Model Parameter, and Root Mean Squared Error