To kick things off this week, we are discussing the benefits of an MRC, or Managed Release Concept, stormwater BMP. For starters, it’s important to understand what a BMP is. BMP stands for Best Management Practices and encompasses all the different management tactics of stormwater. This includes basins, swales, detention beds, etc. MRC BMPs act just as any other stormwater management concept, except they are always allowing a small amount of flow to be released from the bed. While slowly allowing the bed to drain, an MRC BMP still allows for evapotranspiration and infiltration like a traditional BMP. So, why do we even use MRCs? Shouldn’t we be trying to infiltrate all the stormwater we can? The answer is that MRCs work wonders on sites with poor infiltration. They are project saving for any development, small or large, riddled with poor soil conditions.
Typically, when we develop a site, we need to compare the pre-construction runoff to the post-construction runoff. In short, we model and calculate the impact that developing a site has on the runoff. After we create this model, we can work through possible ways to manage the increase in runoff. When a site has great infiltration, the size of the BMP gets smaller, and the project becomes easier to deal with, and vice versa for poor infiltration. Using traditional stormwater beds, basins, or other management tactics, we need to infiltrate that difference of runoff. When successfully done, the BMP methodology and calculations are recorded and reported to the township and/or the DEP. That right there is the design process – consolidated a large amount of course – of stormwater management. The beauty of an MRC BMP is that all the volume passing through the BMP is counted as managed. It does not matter if the excess stormwater is being handled through infiltration or evapotranspiration – if the rate of the discharge is controlled, then that difference of runoff is handled.
So next time you take a peek at what site conditions you’re working with, make sure to ask if an MRC may help your site!