Extreme Rainfall Event Swales

Extreme Rainfall Event Swales

Last Modified: 02/19/2021 07:19 PM

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PROJECT DESCRIPTION 

In early 2021, the Harris County Flood Control District completed construction of extreme rainfall event swales on six vacant buyout lots in flood-prone areas of the Cypress Creek watershed. Construction began in late December 2020 and was completed in January 2021. Turf establishment follows construction.

Extreme rainfall event swales are shallow channels that help direct stormwater that collects inside neighborhoods during heavy rain events. This can happen when storm drains are overwhelmed, and when stormwater sheetflows (crosses overland) to reach a bayou, creek or drainage channel.

These shallow, gently sloping swales connect the street to the nearby bayou or channel in key locations, providing a way to reduce street ponding and other flooding risks.

The swales are grass-lined, approximately six inches to 12 inches deep, and are designed to engage during extreme rainfall events of approximately 5-7 inches.

Swale locations and how they were chosen

Flood Control District staff initially examined 348 potential sites in the Cypress Creek watershed. All were:

  • Located within the 1 percent (100-year) floodplain
  • Within 500 feet of a Flood Control District open channel
  • Involved in repetitive flood losses
  • Built prior to 1984 per Harris County Appraisal District records*
  • Not within 2018 Bond Program Subdivision Projects areas

Following this analysis, it was determined to consider only Flood Control District buyout lots. After field assessments, six vacant buyout lots in flood-prone areas were chosen. All are near and flow into a tributary of Cypress Creek. Click this link for the map.

  1. 13650 Salt Grass Trail, Dry Creek K145-00-00
  2. 18811 Casper Drive, Lemm Gully K120-00-00
  3. 17811 Butte Creek Road, K129-00-00
  4. 17823 Butte Creek Road, K129-00-00
  5. 17922 Pinto Circle, K126-01-00
  6. 19402 Enchanted Oaks Drive, Senger Gully K120-01-00

*Subdivision regulations changed in 1984. In 1984, developers were required to design subdivisions to address extreme rain events. Post-1984 neighborhoods already have swales, or streets were sloped to the nearest stormwater detention basin or channel so as to prevent ponding.

Extreme Overflow Swale Sites

Phase 3: Field Assessment Results (6 Proposed Sites)