The Impacts of Storm Water Runoff on Water Resources

Historically, much of Montana’s rainwater and snowmelt stayed where it fell, soaking into healthy grassland and forest soils to replenish groundwater and, eventually, making its way to our rivers and streams. Today, rainwater in developed areas is often sent directly into storm sewers where it is flushed into our streams and rivers along with pollution from roads, parking lots, or yards. As we add more roofs, pavement, and compacted turf to our communities, it is more important than ever to help rainwater infiltrate the soil to minimize flooding and protect water quality.

In typical urban settings, soils are heavily compacted from the development process. Land is also covered with impervious surfaces, such as roofs, streets, and sidewalks. Consequently, land is unable to absorb storm water. Instead, storm water is collected and conveyed as quickly and efficiently as possible to surface waters. This speeded-up process concentrates and delivers urban pollutants such as sediment, hydrocarbons, metals, bacteria, and fertilizers to our streams, rivers, and lakes. These waters serve many uses including drinking water and recreation.

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Last Modified: 07/05/2007