Stormwater is water on land surfaces that originates from precipitation. It is a natural and important part of the hydrologic cycle. Some precipitation soaks into the ground and becomes part of the soil moisture. Most of it runs over land and arroyos or through streets, channels and drains.

A watershed is a land surface that produces stormwater runoff during precipitation. The flow accelerates as it drops in elevation, and increasing amounts of debris are carried by the stream. A large amount of precipitation in a small watershed produces a destructive stream of stormwater runoff. The combination of speed plus debris increases the destructive force of the flows.

Flooding occurs when stormwater runoff exceeds the capacity of an arroyo or channel. Adverse impacts include dislocation, property damage and loss of life. Damage from runoff can be curtailed by implementing the following:

• land use development controls and open space planning
• erosion controls that limit the amount of rocks and
• debris washed away with the runoff
• structural flood control systems
• stormwater systems

A stormwater system is designed to minimize flooding. It collects stormwater runoff, dissipates energy (reduces speed of flowing water), removes debris, and safely channels the flow to a designated collection point or receiving stream. El Paso's stormwater system includes man-made and natural features.

Natural arroyos provide a stormwater runoff conveyance with built in energy dissipation and debris removal features. Some arroyos are protected from development and remain as natural channels. Natural depressions can also be used to retain stormwater runoff. These areas can be integrated into the stormwater system while being preserved as wilderness areas.

Detention ponds are a key part of the stormwater system. They retain water, dissipate energy, percolate stormwater into aquifers and remove debris. Historically, ponds were narrow, deep and fenced to keep people out.

Recently, they have been made wide and shallow, so grass, trees and other park features can be incorporated. More detention ponds will be constructed as park ponds. This allows them to retain their stormwater function and increases the number of city parks.

El Paso's stormwater system has the following major components:

• pump stations – 22
• ponds – 482 (2,102acres)
• dams and basins – 37 (1,822 acres)
• channels – 75 miles
• agricultural drains – 13 miles
• storm drain conduits – 363 miles
• storm drain drop inlets – 8,039

Sewer pipes capture used water and liquid waste from homes and businesses and carry it to wastewater plants for treatment. Treated wastewater can be reused for landscape irrigation, industrial and construction purposes. It also helps sustain the aquatic habitat of the Rio Bosque wetlands and provides water for farming in the Mission Valley.

Storm drains are separate from the sewer system and, unlike wastewater, stormwater is not treated and reused. Storm drains carry runoff to the Rio Grande and retention basins. Some storm drains are under streets, but much of the system consists of open canals, street gutters and other features that collect, channel and divert stormwater runoff.

Stormwater fees fund system maintenance and construction projects, and residents are better protected in both the short and long term. Areas that historically flooded were evaluated, and solutions are being pursued. The system also benefits from increased maintenance. Preventive maintenance continues to be a priority, and crews work throughout the year to keep the system clean. Maintenance reduces flood risk by reducing blockages and overflows.

Ten percent of annual stormwater fee revenue is used for projects that preserve open space and greenways while channeling or retaining stormwater runoff. The funds set aside for green projects also help fund park pond projects.

Stormwater fees are assessed for property owned by organizations, El Paso County and city government and El Paso Water, as well as commercial, industrial and residential properties. Federal and state agencies, public institutions of higher education, the Housing Authority of the City of El Paso and independent school districts are exempt, as well as undeveloped lots and agricultural land. Churches and nonprofit social service agencies are billed at a reduced rate.

The fees are used only for stormwater utility expenses. They fund system operations, maintenance and capital improvement projects, as well as open space and green projects. Fees are based on the amount of impervious surface areas.

Impervious surfaces includes any nonporous area that has been disturbed from its natural condition in a way that reduces the ability of the surface to absorb water into the soil. Examples are compacted soils, buildings, pavement, parking lots, driveways, sidewalks and other man-made structures or surfaces built or laid on the natural surface of the land that alter stormwater runoff so that flows are increased. For billing purposes, turf, xeriscaped areas, driveways, walkways and sidewalks are not included.

The impervious area of properties is determined by using aerial photographs and information in EPWater's Geographic Information System, along with El Paso Central Appraisal District real property Information.

For residential property, impervious area refers to the ground floor of the house, garages, porches, patios, and any additional buildings, storage sheds or other areas that cannot be penetrated by rain; however, driveways, sidewalks, turf and xeriscaped areas are not included in the calculation.

As with all public infrastructure, the stormwater system benefits all residents because they all travel on El Paso's streets and highways and benefit from stormwater control. Therefore, all residents pay to improve and maintain the system; however, credits are available for properties with onsite ponds that capture and retain stormwater.