What is Stormwater?
Stormwater is water on land surface that originates from precipitation. It is a natural and important part of the hydrologic cycle. Some precipitation will soak into the ground and become part of the soil moisture. Most will run over the land surface and arroyos, through streets, or through engineer-built channels and drains.
The land surface that produces runoff during precipitation is called a watershed. A large amount of precipitation in a comparatively small watershed can produce a stream of stormwater runoff that is destructive. As runoff flows drop in elevation, gravity accelerates the flow. Furthermore, as flows accelerate, increasing amounts of debris are carried by the stream. The combination of speed and debris increases the destructive force.
Floods are among the most devastating of natural disasters. Flooding occurs when stormwater runoff exceeds the capacity of the arroyo or channel conveying the flow downstream. Adverse impacts from floods can include loss of life, property damage and dislocation. Damage from runoff can be curtailed by implementing the following: 1) land use development controls and open space planning, 2) erosion controls to limit debris entrainment, 3) structural flood control systems, and 4) stormwater systems.
Stormwater systems include dams, holding ponds, conveyance pipes, open channels, pump stations and streets. The purpose of a stormwater system is to collect stormwater runoff, dissipate energy (reduce speed), remove debris, and safely channel the flow to a designated collection point or receiving stream. El Paso’s stormwater system includes approximately 275 ponds, 16 pump stations, 39 dams plus miles of conveyance channels of all types.
Arroyos and Open Space
Arroyos provide a natural stormwater runoff conveyance with built in energy dissipation and debris removal features. Some arroyos will be protected from development and set aside to remain as natural channels. In addition to arroyos, natural depressions can also be used to retain runoff. These areas can be integrated into the stormwater system while preserving the space as a wilderness area. Ten percent of the stormwater fee revenue is used to acquire and maintain these precious open spaces.
Detention ponds are a key part of the stormwater system. They retain water, dissipate energy, percolate stormwater into the aquifers and remove debris. Historically, ponds were narrow and 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 made into park ponds. This allows them to retain their stormwater function and increases the number of parks in our city.
Maintenance is a critical component of a successful stormwater system. Channels, dams and culverts must be kept clear of debris. Pump stations must be tested and maintained to insure proper function in the event of a storm. Each component of the stormwater system, from the largest dam to the smallest inlet grate in the street, is cataloged and placed into a computerized maintenance management system. The system generate work orders on a regular basis, so personnel and equipment are used most efficiently and the system stays in working order.
The second critical component of a successful stormwater system is a good master plan. URS, an internationally known engineering firm was engaged to develop El Paso’s first master plan. The master plan divides the entire city and some areas outside the city into drainage basins. Each basin was analyzed, and projects were recommended to improve the efficiency of the stormwater system. The projects will be incorporated into the capital improvement program over the next ten years.