GIS-based integration of SWAT and REMM for estimating water quality benefits of riparian buffers in agricultural watersheds

The Soil and Water Assessment Tool (SWAT) is a process-based, watershed-scale model with a hydrologic response unit (HRU) as the basic computation element, which makes it difficult to accurately represent riparian buffers using their physical parameters (e.g., vegetation structure). On the other hand, the field-scale Riparian Ecosystem Management Model (REMM) provides the opportunity to consider details of hydrologic processes within a riparian buffer zone. However, the runoff and its associated constituents from the upland area that is hydraulically connected to the riparian buffer zone must be provided as inputs into REMM. The rationale proposed here is that the integration of SWAT and REMM would improve the assessment of riparian buffers, which is vital to watershed management but which has not been described in the literature. The objective of this study was to develop a GIS interface that integrated SWAT and REMM for estimating water quality benefits of riparian buffers in agricultural watersheds. For modeling purposes, the interface subdivided a watershed into a number of sub-basins, each of which was further subdivided into drainage areas of isolated impoundments (e.g., wetlands), concentrated flow, and riparian buffers using available GlS data. As a result, riparian buffers received runoff and associated pollutants from corresponding contribution areas to mimic actual field conditions. The interface facilitated transferring the SWAT outputs into REMM and computing the site characteristic parameters (e.g., length and width) of the riparian buffers. The outputs from subsequent REMM runs were in turn taken as inputs into SWAT for channel routing and further simulation. The interface was used to assess water quality benefits of riparian buffers in the Lower Canagagigue Creek watershed located in southern Ontario, Canada. The results indicated that the existing riparian buffer system achieved a 27.9% abatement in sediment and a 37.4% reduction in total phosphorus. The model runs demonstrated that the GIS interface was easy to use and could serve as a protocol for integrating models with distinctly different spatial scales. © 2007 American Society of Agricultural and Biological Engineers.