In support of this effort, The Land Conservancy asked Waterways Consulting, Inc. to evaluate potential future hydrologic and erosion impacts at Attiyeh Ranch if the property was not conserved but was instead converted to more intensive land uses, such as intensive cattle ranching, viticulture, or ranchette properties. To understand the water supply benefits associated with protecting Attiyeh Ranch under its current level of land use and limited future land use changes, a hydrologic model (HEC-GeoHMS) was developed for the project area. The hydrologic model was used to evaluate changes in runoff volume under the following four land use scenarios: existing conditions, intensive grazing, vineyards, and ranchette/hobby farms.
An erosion and sediment delivery model was also prepared for the subwatersheds within the ranch to evaluate how changes in land use on the ranch would change rates of erosion and sediment delivery to the mainstem Nacimiento River and its tributaries. The erosion modeling was based on work that was conducted in the Morro Bay Watershed over the past few decades in support of a total maximum daily load. Percent increases in sediment generation from the ranch were calculated for each potential land use scenario as compared to existing conditions. The results from the hydrologic and erosion models were used as input to a cost benefit analysis for purchase of the property.