River Basin Characteristics
The Tiffin River watershed is 778 square miles and is located in southeast Michigan (22 percent) and northwestern Ohio (72 percent). The Tiffin River is 118 miles long, but the watershed is approximately 53 miles long and 23 miles wide. It represents almost 8 percent of the Maumee River basin. It flows southward from the Irish Hills in Michigan to the Maumee River near Defiance in Ohio.
The watershed is mostly flat. Approximately 56 percent of the watershed has slope of less than 1 percent and only 11 percent has slopes greater than 4 percent. The major tributaries of the Tiffin River are Lick Creek, Brush Creek, Beaver Creek, Mill Creek and Bean Creek.
The watershed drains a primarily rural farming region, with 51 percent of the land being cropland. The main productions are soybeans, corn and wheat. There are also several dairy farms. The rest of the land is forest (17 percent), grassland (14 percent), and urban (17 percent). Less than 1 percent is open water, wetland and barren. The main sources of impairments are siltation, habitat alteration, organic enrichment and low dissolved oxygen.
For this project, the TRSWAT (Tiffin River SWAT) was developed. The model was built to simulate streamflow, sediment and nutrients (phosphorus and nitrogen) for the 2000-2011 period. The initial datasets used for the model were based on what could be representative during that time period.
Some modifications were made to the initial model to have a better representation of the reality. Because there were large gaps in weather information, the gap filling approach was modified. Instead of using climate input data estimated by the SWAT weather generator, values from the nearest climate station were used. The Devils Lake and Round Lake reservoirs were placed in separate subbasins during the watershed delineation because SWAT only allows one reservoir per subbasin.
Refined agriculture inputs for the calibrated TRSWAT model were also used: tillage data, ephemeral gullies, manure, and commercial fertilizer applications. The tillage assignment approach was adopted for TRSWAT because it ensures that the overall distribution of tillage types represented in the model for a given crop type and year are generally consistent with the distributions reflected in the NRCS transect point dataset used.
The development of model inputs to represent ephemeral gully features initially involved the use of a set of high-resolution set of digital elevation models available from the Ohio Statewide Imagery Program. Because similar high-resolution models data were not available for the Michigan portion of the watershed, a modified approach was employed for that part.
The nutrient availability of nitrogen and phosphorus from manure application is based on the standard values in SWAT for dairy manure, which was selected to represent both dairy and swine manure given the dominance of dairy cows in the watershed. To account for the manure generated and applied within the watershed, every acre of conventional-till and reduced-till corn was assumed to receive nitrogen and phosphorus through manure application in the fall.
Use and Applications
The TRSWAT model was developed, calibrated/confirmed, and applied to evaluate reductions in sediment and nutrients for a range of land management actions.
The primary objectives of the project were:
- Quantify the sediment and nutrient loading from the Tiffin River watershed;
- Determine the spatial and temporal distribution of sediment and nutrient sources and important pathways of export in the watershed;
- Estimate the potential benefits of best management practices (BMPs) and land conservation management actions; and
- Support broader sediment and nutrient modeling efforts of the lower Maumee River and Maumee Bay.
The application of the refined SWAT model to the Tiffin River watershed provided a detailed analysis for a complicated problem over a large watershed system. The model provides a powerful and useful science based tool for future decision making regarding best conservation practices in the Tiffin River watershed.
For more Information:
USACE, Buffalo District
1776 Niagara Street
Buffalo, NY 14207
Phone: (716) 879-4488