Stormwater is the word used to describe water on the surface that originated from precipitation. Some amount of that precipitation will soak into the ground and will become part of the soil moisture. Most will run over the land surface and arroyos, through streets or through engineer built channels and drains. Stormwater is a natural and important part of the hydrologic cycle. The land surface that produces runoff during precipitation is called a watershed. A comparatively large amount of precipitation in a comparatively small watershed can produce a stream of surface runoff that is destructive. As the surface runoff flow drops in elevation, gravity accelerates the flow. Furthermore, as the flow accelerates, increasing amounts of debris is carried by the stream. The combination of speed and debris increases the destructive force.

Storm 2006  Doniphan heavily flooded on the Westside of El Paso

Flooding occurs when the surface 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. Floods are among the most devastating of natural disasters.

In order to reduce the potential damage from surface runoff, mitigation of adverse impacts can be implemented including 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) storm sewer systems.

Storm sewer systems include dams, holding ponds, conveyance pipes, open channels, pump stations and streets. The purpose of a storm sewer system is to collect surface runoff, dissipate energy (reduce speed), remove debris and safely channel the flow to a designated collection point or receiving stream.

The storm sewer system in El Paso consists of approximately 250 basins, 16 pump stations, 20 dams plus miles of conveyance channels of all types.

Arroyos and Open Space

In recognition of the fact that arroyos provide a natural surface 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. Furthermore, in addition to arroyos, natural depressions can also be used to retain surface runoff and can be integrated into the management system while preserving the space as a wilderness area. A certain percentage of all stormwater utility fees collected will go to acquire and maintain these precious open spaces.

Park Ponds

Detention ponds, which are a key part of the storm sewer system are designed to retain water, dissipate energy, percolate stormwater into the aquifers and to remove debris. Historically, these structures have been narrow and deep and have been fenced to keep people out. Recently, these structures have been made wider and shallower to allow the planting of grass and trees and other park features. More of these detention ponds will be made into park ponds. This will allow them to retain their storm sewer function and will increase the number of parks in our city.

Maintenance

Maintenance of stormwater facilities is one of the key critical components of a successful system. Channels, dams and culverts must be kept clear of debris. Pump stations must be tested and well maintained to insure proper function in the event of a storm. Each of the components of the stormwater system, from the largest dam to the smallest inlet grate in the street must be cataloged and placed into a computerized maintenance management system. The system will generate work orders on a regular basis. This way personnel and equipment are most efficiently utilized and the system stays in working order.

Planning

The second key critical component of a successful system is a good master plan. Currently, a master plan for the stormwater system does not exist. URS, an internationally known engineering firm has been engaged to develop a master plan. The master plan will divide the entire city and some areas outside the city into drainage basins. Each basin will be analyzed and facilities proposed to carry a 100 year storm event. The master plan will be the basis for follow-on design and construction projects. For the year 2008 we will focus on development of the master plan. In the following year, 2009, we will focus on design of projects described in the master plan. By year 2010, major construction will begin for those facilities.