Flood Studies

Dodson & Associates, Inc. is recognized as a leader in providing comprehensive flood protection plans and studies for cities, counties, and special districts. Some of these plans include the entire jurisdiction of a particular political entity; others deal with only one watershed. In all cases, however, these plans include comprehensive hydrologic and hydraulic analysis, consideration of structural and non-structural flood control alternatives, careful preparation of implementation plans which include short-range as well as long-range goals.

Brays Bayou Re-Study

Federal Emergency Management Agency

Dodson & Associates, Inc., as a part of a joint venture, is preparing a re-study of the Brays Bayou watershed in Harris County, Texas.  The study serves as a pilot project for additional re-studies to be completed in the future.  The results of the study include updated flood hydrologic and hydraulic modeling data for the watershed and updated flood plain maps that are based on the same up-to-date topographic data on which the updated hydraulic models are based.  In addition to providing the final mapping results, the study is establishing methods, procedures, criteria, and requirements for future study efforts in Harris County and other areas in the U.S. that are subject to ground subsidence.  The project also includes an analysis of the effects of subsidence on flooding depths in the Brays Bayou watershed.  In addition to these issues, the project includes traditional hydrology and hydraulic analyses such as unit hydrograph preparation, definition of design storms and floods, flood and reservoir modeling, rating of hydraulic structures, backwater profile computations, and flood plain mapping.  

The scope of the study is extensive.  It includes the main channel of Brays Bayou as well as several major tributaries.  In all, approximately 67 miles of channels with 165 roadway crossings is being analyzed.  To efficiently perform such a large project, relatively new technologies will be used.  The scope of work involves a completely digital database of ground elevations and other data.  Much of this data has been obtained by LIDAR sensing technologies.  Global Position System (GPS) surveying technology is being used for on-ground data collection.  The latest in Geographic Information Systems (GIS) computer software provides for collection and processing the data as well as generating digital terrain models of each flood plain area.  Using these digital terrain models, data is directly transferred to up-to-date hydraulic analysis software for computing water surface elevations.  The resulting flood plain boundaries are delineated automatically, again using GIS technologies.

This completely digital FIS approach is consistent with FEMA’s move toward digital technology for processing requests for map changes.  More accurate study results, faster study completion, and easier study revision all result from these new procedures. <<< Select image to enlarge

Tropical Storm Allison Recovery Project (TSARP)

Harris County, Texas

Dodson & Associates, Inc. will be providing technical support services for the Tropical Storm Allison Recovery Project.  Dodson & Associates will provide technical advice and consultation to the entire project team regarding base mapping, hydrology, and hydraulics. This will include the development and presentation of technical training sessions to other team members. It will also include responsibilities for quality assurance and consistency of data and methods used in various parts of the County.  We will provide technical support for those using the various computer programs required for this analysis. This technical support includes providing the latest available program versions and documentation, and maintaining contact with the program vendors about program updates and other important information.  We will generate a preliminary set of stream channel locations for Harris County, using available digital topographic data. We will compare the stream system with the streams included in earlier Flood Insurance studies.  Dodson & Associates, Inc. will play a very active and aggressive role in providing quality assurance reviews of mapping products, and in working with the study contractors and other team members to integrate different map-based data sets and place them in a format that is readily available for use by team members.  We will provide guidelines for modeling the June 2001 flood event using the hydrologic models developed for the restudy effort.  We will prepare and present a two-day seminar for the hydrology teams for the purpose of discussing the findings from the previous effort and providing direction.

Visit the project website for more information at: www.tsarp.org

Hurricane Creek Analysis

Lufkin, Texas

Hydrologic and hydraulic analyses completed in an effort to identify existing flood hazards in the Hurricane Creek watershed in Lufkin, Texas and to develop a plan for mitigating those flood hazards. The major objectives of the planning studies are as follows:

-           To provide flood plain and floodway data for the purpose of updating the Flood Insurance Rate Maps for the City of Lufkin.

-           To develop a long-range drainage plan for each watershed that accommodates future development without exacerbating existing flooding problems and provides relief from existing drainage problems.

-           To develop a plan for implementing short-term drainage (interim) improvements to address the most critical existing flooding problems in the watershed.