Gridded Surface Subsurface Hydrologic Analysis (GSSHA) Model Simulation of Hydrologic Conditions and Restoration Scenarios for the Judicial Ditch 31 Watershed, Minnesota.

摘要

The purpose of this demonstration was to simulate the hydrology of a small, extensively ditched and tiled agricultural watershed located in western Minnesota (Judicial Ditch 31) using the physically based, multi-dimensional watershed hydrology model: Gridded Surface Subsurface Hydrologic Analysis Model (GSSHA). The original GSSHA model, which solves a one-dimensional form of the Richard's Equation to estimate groundwater recharge, was modified to allow a simplified infiltration/soil moisture accounting routine (Green and Ampt with Redistribution) to provide recharge values. The modified model was then applied to the Judicial Ditch (JD31) watershed in an effort to simulate both surface water runoff and subsurface (i.e., primarily tile drainage) flow. The location of the network of tile drains was determined by modeling the basin with only the ditches, and defining ponded areas in the watershed as regions drained by subsurface tiles, since no water currently ponds in the watershed. These tile drainage areas were then simulated by: (a) modeling them as highly porous soils to simulate the present lake ponding on land surface (Model 1), and (b) modeling the tile drains as a network of small, rough channel sections (Model 2). These two models were calibrated against observed data for the period of June through July 2000. Both models were capable of representing smaller events and baseflow. Model 2 provided better representations of larger events, especially the storm volumes. Model 1 was used to estimate the effects of wetland restoration on surface ponding for wet, dry, and normal rainfall using the June - July period. The tile drainage areas were divided into four regions within the watershed and the effects of restoring 25, 50, 75, and 100 percent of the original wetland areas on surface ponding were examined.