Extra attention to 500-year flood plains - University Green example

A University Green resident via social media pointed out an example of repeated flooding outside of any Special Flood Hazard Area (SFHA) and away from any bayous.

University Green is located in the southeastern portion of Clear Lake City immediately south of the University of Houston - Clear Lake campus. It is adjacent to the western border of Johnson Space Center (see first map).  

Drainage from the area flows into a ditch that runs southward ultimately connecting to Cow Bayou near the intersection of El Camino Real and East Medical Center Boulevard.

The resident mentioned repeated episodes of patio homes being flooded in the central portion of the neighborhood in the vicinity of Ivy Grove and Plumbwood (see second map).


The zoomed-in view shows that the 500-year flood plain (zone of 0.2% Annual Chance Flood Hazard) extends into this area from the east.  There is a bowl-shaped low area that is coincident with Barleton Way and Plumbwood Way.  During heavy rainfall water will enter this depression from Ivy Grove to the northeast and remain trapped until it dissipates via storm drains.  There is a similar feature covering Doverwood Way and Dale Oak Way immediately towards the south.

It appears that the flooding issues in this area are exacerbated by the topography.  There is also a very large area of open land on the Johnson Space Center property that would be susceptible to ponding during storms as shown by the 500-year floodplain. Depending on the inundation depth and rate of rainfall this could hinder drainage from University Green.

This example shows that given the increased frequency of 500-yr (and greater) storms in recent years residents may want to place more emphasis on the location and configuration of the 500-year flood plains and not just the SFHAs.  








Comments

Post a Comment

Popular posts from this blog

Considerations for neighborhood protected by levee

Image
Residents and potential home buyers in areas where protection from flooding is provided by levee systems may need to consider carefully the actual risk, which may be higher than many assume.  Levees are designed to reduce (but not eliminate) flooding risk.  There may often be no requirement for residents to be provided with an assessment of the specific risk by developers. However, the presence of levees indicates that significant drainage issues exist in the area. The levee system (usually composed of earthen berms, flood gates, and pumps) must perform two functions successfully to prevent flooding: Hold back flood water from outside of the protected area Remove water accumulating inside the protected area Failure of the levee system can result from multiple factors such as: Berms must have sufficient height and strength to hold back impinging flood water Gates must operate properly and be opened/closed at the appropriate times  Pumps must operate properly ...
Read more

Check flood control and drainage improvement projects in your area

Image
Residents of flood prone areas are well advised to stay informed regarding current and planned flood control and drainage improvement projects.  These projects by design will result in significant reductions to flooding risk.  In some cases the flood hazard maps will be revised to reflect the reduced risk.  This could allow a decrease in flood insurance premiums for the home owner. In my area I noted a project underway in Nassau Bay, a waterfront community in southern Harris County, Texas that has a history of repetitive flooding.  The project is being conducted by Harris County Flood Control District (HCFCD).  It is located on a lot that I had noted previously as the site of a home buyout and demolition after Hurricane Ike, which caused heavy damage to many Nassau Bay homes in 2008. HCFCD maintains an interactive map viewer on which the details of all Maintenance and Capital Improvement projects can be viewed at the link: https://www.hcfcd.org/int...
Read more

Drainage features without mapped flood plains

Image
All drainage features whether natural or man-made have flood plains, which are simply the adjacent low areas that fill with water during periods of overflow.  Water overtopping the banks will move to all connected lower areas and remain until drained away by other features.  However, these areas may not be mapped as flood plains on Flood Insurance Rate Maps (FIRM).  As a result, residents and property owners may not realize that they are located in a flood zone. Although unmapped these areas will flood during times when the nearby drainage features overflow. This issue was featured in an April 1, 2018 front page article in the Houston Chronicle article entitled "Damage outside flood plain exposes flaws - 'We just need to start again,' says professor about maps designating flood-risk areas".  The article was written by David Hunn, Matt Dempsey, and Mihir Zaveri and can be viewed at the link below: https://www.houstonchronicle.com/news/article/In-Harvey-s-delu...
Read more