Flooding

Everyone living in the Houston-Galveston region resides in a watershed given to flooding. A watershed is a land formation that makes possible the natural drainage of an area into a specific body of water, which for Houston is usually a bayou or stream.

There are 22 watersheds and 35 communities in the Houston area. Where flooding cannot be prevented, the issue becomes how best to prepare for and properly manage flood waters. How well flooding is reduced is determined by the efficiency of the drainage system, a network comprising the channels, storm-water detention basins, bayous, ditches, street drains, underground drainage pipes, and sewers that carry rain water out of neighborhoods. Most of the work being done to manage flooding is in assessing areas that are at a higher risk of flooding than others.

Flood control experts are setting aside natural areas for passive recreation, such as hiking along trails and enjoying scenic views. Construction of storm-water detention basins and channel modifications are also two common ways of reducing the risk of flooding, as is the voluntary buyout of structures that were originally constructed in the flood plain, before today’s regulations.

Wetland mitigation

Mitigation areas are lands that have been bought for transformation back into natural settings, mainly wetlands, to preserve habitat. In the process, the land regains some or all of its function as a floodplain during flooding season. Instead of preserving small lots or pocket areas of natural habitat, which limits habitat’s ability to flourish naturally and confines the movement of species, mitigation areas create one large preservation area more nearly able to function as a natural ecosystem.

The Harris County Flood Control District’s Greens Bayou Wetlands Mitigation Bank, which is a man-made nature preserve with wetlands mitigation, has been successful. Particularly telling are the many animals that have begun resettling the preserve. Phase 1 of the Greens Bayou Wetlands was undertaken in 2004 on roughly 200 acres of land in northeast Harris County. The space combines the natural setting of a wetland with run-off treatment to improve storm water quality. The project calls for six more phases and the creation of 1200 more acres of wetlands.

In coastal areas, subsidence has been a problem, with sinking areas making some homes more susceptible to flooding. Some individuals have built bulkheads to prevent erosion and protect against flooding. For more information on subsidence, see the section on Water Quality.

There are many entities in the region involved with flood control. In general, a city is in charge of drainage in neighborhoods and along city streets and ditches wherever it owns the roads. Other agencies, such as the Harris County Flood Control District, have flood control responsibilities when flood waters reach the bayous or other bodies of water.

Drainage Fee

A proposed drainage fee that would have been used for maintaining city drains and solving other flooding problems was killed by Houston City Council. Instead, funding for such projects was added to a water bill.

Harris County Flood Control District

HCFCD is not a regulatory agency. The city regulates development, and private developers are responsible only for ensuring that construction will not create or exacerbate current flooding conditions; they are not held accountable for already present flood risks. HCFCD’s responsibility is to attempt to manage flooding, not to prevent it by imposing restrictions.

Nevertheless, HCFCD has been restudying the flood risk in Harris County by mapping and assessing the region’s flood patterns. The data collected is used in conjunction with a newly approved (October 2004) Criteria Manual so that developers for HCFCD and others can build more flood-resistant projects. HCFCD, together with local partners, is about to start a study that will look backward to see whether previous criteria and regulations are working.

Three methods of flood reduction have been particularly effective. Most often used is channel enlargement. In this approach, a section of a bayou is widened and planted again with grasses or other material. A second method is to create storm-water detention basins, which handle overflow until water surface levels are low enough to move safely through the bayous. Third, home buyouts are increasingly used to reduce the risk of flooding. Agencies or other organizations buy houses located on flood plains, and development is restricted in the area to keep it as a natural flood plain. As agencies buy house by house, checkered neighborhoods begin to emerge. Some have used the land for community gardens, and tightly squeezed neighborhoods with small yards have installed recreational areas. Landscaping agreements can be entered into with HCFCD.

HCFCD has been working with the Katy Prairie Conservancy to buy flooding easements. There has been some work, too, with Armand Bayou.

Mapping

The Tropical Storm Allison Recovery Project is a multi-year joint study effort by the Federal Emergency Management Agency and the Harris County Flood Control District. The TSARP project will comprehensively assess the flood risks associated with major flooding sources within Harris County and develop technical products that can assist the local community following devastating flooding. An end product of the study will include new flood insurance rate maps, with new delineations of special flood hazard areas, so that the public, government officials, and other Harris County stakeholders can make informed flood management decisions about the places where they work and reside.

New technology

The agencies are using innovative scientific techniques to determine the current flood risks posed by streams and bayous throughout the county’s approximately 1,700-square-mile area.

LiDAR, a new light detection and ranging device developed by NASA, is mapping flood plains. The device projects millions of laser signals at the ground from low-flying aircraft in order to measure the elevation of every 15×15-square-foot surface throughout Harris County. The technology is being used to identify areas that are at a higher risk than others by providing a detailed representation of the shape and layout of the ground.

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