Riparian Ecosystem Management Model (REMM): I. Testing of the hydrologic component for a Coastal Plain riparian system

The Riparian Ecosystem Management Model (REMM) was used to simulate shallow groundwater movement, water table depths, surface runoff, and annual hydrologic budgets for a Coastal Plain riparian buffer system near Tifton, Georgia, USA. The riparian buffer consisted of zone 3 (grass downslope from a row-crop field); zone 2 (mature pine forest downslope from zone 3); and zone I (mature hardwood forest downslope from zone 2, adjacent to stream). Measured surface runoff and shallow groundwater movement from the adjacent agricultural field were used as the hydrologic input to REMM. Uncalibrated simulation results for a five-year period were compared to measured values for the same time period. The overall error in zone 2 and zone 1 mean water table depths was about 0.07 m, although absolute errors were higher The water table dynamics simulated by REMM were similar to observed although lags were observed in the response of the simulated water table to large rainfall events. Mixed results were obtained from observed versus simulated surface runoff comparisons, primarily due to large variability in observed runoff depths along the riparian transect. Simulated surface runoff depths for zone 3 were within one standard deviation for four out of the five years. For zone 2, surface runoff depths could only be simulated within one standard deviation for two out of the five years. Simulated seasonal total depths of surface runoff did not always agree with observed values but usually followed both similar temporal and spatial patterns. Annual hydrologic budgets produced total streamflow comparable to those estimated for the riparian buffer site. These results provide an adequate basis for subsequent testing of other REMM model components including water quality and nutrient cycling.