Minnesota Stormwater Manual test page 5
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Default TSS and TP loads using the MPCA Simple Estimator
The objective of this analysis was to provide estimates of annual loads of total phosphorus (TP) and total suspended solids (TSS), in pounds per acre, from stormwater runoff in Minnesota cities. The results represent estimated loads with no implemented best management practices (BMPs).
Analysis
We used the MPCA Simple Estimator (Estimator) to calculate average annual loading, in pounds per acre, for total phosphorus (TP) and total suspended solids (TSS). We used the default values in the Estimator for event mean concentration and runoff coefficient and assumed an annual average precipitation of 30.65 inches (Twin Cities Metro Area (TCMA)). These values are discussed in the Minnesota Stormwater Manual, as well as guidance for the MPCA Simple Estimator. Appropriate links include the following.
- Event mean concentrations for total phosphorus and total suspended solids
- Runoff coefficients
- Guidance for the MPCA Simple Estimator
We gathered land use data for several TCMA cities using Metropolitan Council land use data. The land use categories for the Met Council data do not match those used in the Estimator, so we converted the Met Council data into land uses used in the Estimator. These are summarized in the following table. Because this is subjective, we include a column describing the relative significance of a specific land use to total acres in a city. For example, farmstead was assigned to agricultural land use. Farmsteads may not be associated with typical agricultural practices, but farmstead is a minor land use and therefore has a minor impact on overall pollutant loading.
Met Council and Manual land use categories
Link to this table
| Met Council land use data | Land use assigned in the Simple Estimator | Relative contribution of land use to total acres in a city |
|---|---|---|
| Agriculture | Agriculture | Low to high |
| Farmstead | Agriculture | Low |
| Golf course | Golf course | Low |
| Industrial and utility | Indutrial | Low to moderate |
| Institutional | Institutional | Low to moderate |
| Major highway | Transportation | Low to moderate |
| Airport | Transportation | Low |
| Railroad | Transportation | Low |
| Mixed use commercial and other | Commercial | Low |
| Mixed use industrial | Industrial | Low |
| Mixed use residential | Residential | Low |
| Multifamily | Residential | Low |
| Office | Commercial | Low to moderate |
| Open water | Water | Moderate |
| Park, recreational, or preserve | Park | High |
| Retail and other commercial | Commercial | Low to moderate |
| Single family attached | Residential | Low |
| Single family detached | Residential | High |
| Undeveloped land | Open space | High |
| Manufactured housing park | Residential | Low |
| Retail and other commercial | Commercial | Low to moderate |
| Extractive | Extractive | Low |
The Estimator does not have default emcs and runoff coefficients for golf courses and extractive land use. We conducted a brief literature review to determine values for these two land uses. Default values for Estimator inputs are summarized in the following table.
Land use event mean concentrations (emcs) for the MPCA Simple Estimator