Issues

Original Issue: The issue for which the planned research was originally undertaken is the unknown extent of change to storm water flooding throughout the Cypress Creek Watershed as a result of full urban land development within this watershed.

The CCFCC June 2003 grant application submitted to Houston Endowment reads,

“While participating in our advisory role as a TSARP Stakeholders Committee member, CCFCC’s representative quickly learned this $24 million project will result in the flood maps to be published in 2004 being based on the urban “as built” development existing in late 2001when the LiDAR air borne measurements were made. Therefore, for purposes of knowledgeable, effective planning to accommodate land development, disaster loss reduction and emergency preparedness in the immediate and long term future, the TSARP data will be out-of-date at the time of publication in 2004 and become immediately subject to increasing degrees of inaccuracy as unrecorded urban development growth progresses throughout this watershed [emphasis added]. After expressing strong objections to FEMA and HCFCD, the CCFCC collaboration efforts successfully concluded with a recentagreement to use the FEMA-HCFCD TSARP data as a platform for a baseline to model flood scenarios through computer simulationreflecting conditions when the watershed is fully urbanized. This will allow a determination to be made as to where the new TSARP calculated floodplains will expand in the future under “worse case” conditions.” [1]

Additional Issues: As stated above, our original project plan was based on using the computer models developed in theFEMA TSARPprogram “as a platform” for simulation of the urban development “Future Conditions” research. When the project was implemented, the first step taken prior to simulating “future conditions” was a technical review by CCFCC’s consultant to verify the TSARP models calculations were accurate. This verification was done by comparing the TSARP computer model data calculated for peak flood elevations / flow volume and rates to what had historically occurred in the past (informationwhich had been measured and recordedduring actual flood events in l994, l998 and 2001) The findings of Mr. Dunbar’s review concluded that factors intrinsic to these computer models wereresulting in inaccuracies of a magnitude which rendered them as being not suitable for the purpose intended. However FEMA adopted the flawed base flood elevations / floodplains, FIS and FIRMs (flood insurance rate maps) generated by these models; this action thereby creating additional issues as described below: [2]

1. The latent defects, left uncorrected, would carry forward into calculations in the “Future Conditions” research thereby making the “Future Conditions” findings invalid.

2. HarrisCounty issuance of land development permits in areas where the floodplains had been under calculated would unknowinglyallow construction of roads, infrastructure and buildings absent from the requirement to comply with more stringent government flood

mitigation regulations which would otherwise apply ifsuch floodplains were accurately calculated andthe applicable regulations were enforced.

3. NFIP flood insurance mandated per government regulations for developed properties within the 100-year floodplains would not berequired for properties in floodplain areas erroneously omitted onFEMA’s TSARPFIRMs (Flood Insurance Rate Maps).

4. An unknown degree of increase in flood risk to downstreamcommunities as aresult of new developmentin upstream, higher elevation locations being allowed to build and alter the existing topographyin areaswhere identification of the true floodplains had failed to be done as noted above.

5. An unknown degree of error / inaccuracies in identification / quantification of depth, width, volume, flow rates and exact locations in what is known to be the largest overflow area between watersheds throughout all Harris County watersheds. Resolving these ambiguitiesby establishing more precise / reliable data will benefit in improved fact-based land development management of floodwater drainage flowing from WallerCounty andother upperCypress Creek stream reaches into (1) the AddicksWatershed and onward into the Buffalo Bayou system and (2) downstream intoestablished Cypress Creek communities.

6. The improved water quality and flood protection benefits derived from thousands of acres of existing wetlands are at risk of being lost because suchwetlands have not been shown as being within the true 100-year floodplain perimeter; this being the criteria used by the U.S. Corps of Engineers to delineate their jurisdiction in regulating development under provisions of the Clean Water Act. (See Attch. #3 photos).

7. An additional issue independent from the flawed computer modeling calculations mentionedabove became apparent to CCFCC during our consultant’s review of revisions to development regulations governing design and construction of storm water flood mitigation infrastructure; such changes being unexpectedly proposedby HCFCDat a point in time which overlapped start of the “Future Conditions” research. Because such regulations were to be a basic element for which their adequacy would betested during this research, a technical review at that timewas deemed to be prudent. Our consultant advised that under conditions existing within the Cypress Creek Watershed, the rate / volume at which storm water would be allowed by such regulations to be released from flood mitigation detention ponds constructed by land developers would resultin a cumulativeunintended increase in the elevation of floodwaters flowing into areas containing downstream communities.

CCFCC requested a more stringent release rate and submitted supporting technicalrational toHCFCD. It was rejected and their rate (greater by a factor of 10) was adopted by Commissioners Court at that time. If the cumulative increase is actually occurring, it constitutes a serious shortcoming in existing HCFCD storm water management regulations within this unique watershed; a shortcoming that will not be detected by the “Future Conditions” research due to design limitations in FEMA’s existing HEC-HMS computer models capabilities.

Note: Professional experts in the industry believe resolution of this dilemma can beaccomplished through field researchemploying the “No.Adverse Impact” criteria established by the Association of State Floodplain Managers (ASFPM). (Refer to Attch. #13 for more information).

Issues HEI

1

[1] CCFCC letter to Houston Endowments Inc., June 23, 2003, Page 5, 3rd paragraph.

2 Based on recorded actual peak flow depths and locations during major historical flooding, it was determined the FEMA TSARP computers were significantly under calculating these key elements in areas of the Upper Cypress Creek Watershed. Although CCFCC filed an appeal seeking corrective recalibration of the models, FEMA denied the appeal and subsequently officially adopted the flawed models and their corresponding flood data / maps effective June 18, 2007. (Ref: FEMA letter to Judge Robt. Eckels, 12/18/06).