Frequently Asked Questions

At this time, there is no immediate concern with the Brazos River. However, the amount and rate of erosion will vary any given year as it depends on several factors. A few of these include:

• frequency of rain events
• magnitude and duration of future flooding events
• location of the erosion problem

Lack of planning and action could result in the potential of seeing property values impacted, increases in flood insurance rates, and the inclusion of some areas in the floodplain zone. One of the goals of the study is to develop plans to address the issue and reduce future risk to nearby areas.

Areas protected from the Brazos River by levees are not classified as being in the floodplain. As long as the river level is below the top of the levee or the levee is not breached, these areas would not experience flooding from the Brazos River. The ongoing erosion problem could change this.

The amount and rate of erosion will vary any given year as it depends on several factors. A few of these include:

• frequency of rain events
• magnitude and duration of future flooding events
• location of the erosion problem

Lack of planning and action could result in damage to the levee or a negative impact on the level of protection the levees provide. If this happens, there is the potential of seeing property values impacted, increases in flood insurance rates, and the inclusion of some areas in the floodplain zone. One of the goals of the study is to develop plans to address the issue and reduce future risk to nearby areas.

The City is using a the Observation Method for Meandering Prediction (OMM) developed by Dr. Jean-Louis Briaud at Texas A&M University. The methodology includes the following:

• observation of historical movement of the meanders of the river
  Historical maps and aerial photographs are used to determine the river movement (migration) with time. The bank migration is measured using the available aerial photos to perform a historical observation of the river bank movement.
• analysis of representative samples of the soil bank
  Soil samples are obtained at different depths along the critical bank locations to perform soil classification and laboratory testing with the objective of determining the erodibility of the soil at each location. Soils would be classified from very erodible category to non-erodible.
• quantification of the erodibility of the soils (EFA tests),
  A soil sample is collected in a thin-walled tubes (Shelby Tubes).  The soil is put through an Erosion Function Apparatus (EFA) apparatus, to determine their erodibility at different velocity. As a controlled flow of water is push thought he apparatus, the soil is extruded from the Shelby tube and the rate of erosion is determined. The Erosion Function Apparatus (EFA) test uses site-specific soil samples acquired via thin-walled tubes (Shelby Tubes) to generate the erosion rate and shear stress which is plotted to create an erosion plot. The information produced by the test can help an engineer accurately determine the depth of scour or level of bank erosion as a function of time.
• determination of the velocity hydrograph for the period of analysis,
  The river’s flow rate is plotted for different time intervals and different storm events. At each study location, and based on the river’s cross section, the corresponding average velocity for each flow is calculated for each time intervals analyzed. A hydrograph (plot showing the rate of flow versus time past a specific point in a river) is prepared showing the velocity versus time at each study location.
• calibration of the observed migration with predicted migration using the TAMU-OMS software
  This mathematical model based software, was developed by TAMU specifically for determination of erosion rate and river bank migration. It predicts the future migration of a river bank in a period of time based on the actual migration for an earlier time period.
• prediction of average future migration using the fitted soil erosion model
  The velocity data and soil type at each location are used as input for the MEANDER software to predict the average future migration for a time frame.
• performing probabilistic prediction to obtain probability of river meander to a certain location.
  A risk analysis is done using the 100 year and 500-year storm frequency hydrograph as the input values at different locations. The MEANDER software determined the probability of the river to reach a certain point in a giving period of time.
  
  

The stakeholders of the study are:

• Fort Bend County
• TxDOT
• Levee Improvement Districts (LIDs)
• Brazos River Authority

The city is partnering with:

• Greg Wine, PE
  Huitt-Zollars, Inc.
• Dr. Jean-Louis Briaud, PhD, PE, DGE
  University Distinguished Professor and Buchanan Chair Holder
  Zachry Dept. of Civil Engineering, Texas A&M University