Stormwater can pick up debris, chemicals, dirt and other pollutants, and flow into a storm sewer system or directly to a lake, stream, river, wetland or coastal water. Anything that enters a storm sewer system is discharged untreated into the water bodies we use for swimming, fishing and providing drinking water.

Ongoing development around the state contributes significantly to the growing impacts of stormwater. The Dallas-Fort Worth area, for example, has grown substantially in the past 30 years. Consider the images below which demonstrate the expansion of urban areas into rural Texas. These images of Dallas-Fort Worth were taken in 1974, 1989 and 2003.

The buildings, parking lots, roads and other impervious surfaces associated with development lead to increased stormwater runoff. Stormwater runoff from construction sites can cause soil erosion to occur at a rate 20 times greater than normal land use situations. Also, when compared to pre-construction soil erosion, construction disturbance can cause erosion to increase by as much as 1,000 times.

The figure below depicts pre- and postdevelopment runoff discharge rates for a typical storm. The increased runoff can lead to:

• Increased peak discharges.
• Increased volume of storm runoff.
• Decrease in time for runoff to reach stream.
• Increased stream velocities during storm events.
• Increased frequency and severity of flooding.
• Reduced stream flow during periods of prolonged dry weather.