In recent years cities have adjusted how storm water is managed, processing smaller amounts per storm. Montana Post - Construction Storm Water Management provides this information

“Modern-day practices for land development employ various land planning techniques, design practices, and technologies to simultaneously conserve and protect natural resource systems. This multistep storm water management approach uses thoughtful site planning and manages rainfall at its source by using integrated and distributed small - scale BMP’s. This approach is also referred to as low - impact development (LID). While this may not be feasible or the preferred approach for every project, nationally, LID is becoming increasingly popular as the standard for storm water management. It is encouraged in Montana’s General Permit.

Every site is unique and should be assessed on a case - by - case basis to determine whether the LID BMP would be feasible or beneficial, given the site’s characteristics. Examples of these characteristics include soil infiltration rates, frost depth, local precipitation and hydrology, vegetation suitability, winter maintenance considerations, maintenance responsibilities, and regulatory conflicts.”