Parcel Best Management Practice Calculator

Load reduction is estimated evaluating the performance of BMPs on a given parcel of land. The WMT takes input values of BMP type, land use, dimension, capacity, and applies them to the desired parcel’s source contribution values of pollutant load in order to get a reduction value. The difference in the baseline contribution runoff volume/concentration and the post BMP-implementation volume/concentration will provide the user with an estimation of its performance. The user can choose whether the BMP load reduction is evaluated by percent, units, or effluent quality (concentration).

Within the spreadsheet, the user is required to enter the parcel information, which includes the APN, watershed, soil groups, and the type and area of land cover within the parcel. The user selects planned/newly implemented BMPs from a list of 29, and enters the treatment area for each BMP (including the land cover of that treatment area), and for structural BMPs, the depth and storage capacity of the BMP. The user also has the op on to change the default runoff volume and pollutant loads of each land cover type, if needed.

The output is presented in the form of both tables and graphs. It includes a summary table which has the total estimated runoff and pollutant loads, and the total runoff and load reduction of all BMPs. The user is also able to view the load removal of each type of BMP.

• Tool may be used during the implementation phase of stormwater program
• Dry weather flow reductions are based on a percentage reduction, and dry weather flow is assumed to be 100 percent reduced by structural BMPs, unless dry weather flow is noted to be significant
• Benefits of non-structural BMPs are generally based on a percentage reduction
• Tool was originally designed for a rural watershed, and therefore has a focus on agricultural and low density residential areas
• The user is able to note whether an area has already been treated by another BMP, in order to prevent the load reductions from being double calculated
• This tool is free and available to the public

The tool is capable of dry weather load reduction calculations for good housekeeping BMPs (i.e. proper vehicle wash station, proper pool/spa maintenance, etc.)