Costello, Inc. was the prime consultant for the design, analysis, and construction management of the Brazos River - River’s Edge Bend Streambank Protection Project. As District Engineer for Fort Bend Municipal Utility District Number 140 (MUD 140), Costello worked with the MUD board to conceptualize, design, and manage the construction of this project to protect its residents. Costello also assisted the client by preparing and administrating a grant application to provide funding for the improvements. Costello coordinated with several governmental agencies throughout the process to establish design criteria and obtain regulatory approvals. The Costello team provided a hydraulic analysis of the proposed improvements and prepared the project’s final design, including construction plans and specifications, administrated the bidding of the project, and provided construction phase services.
Fort Bend MUD 140 is a special purpose district established by the State of Texas to provide infrastructure for the community of River’s Edge, along the east bank of the Brazos River. A significant meander bend exists at this stretch of the river, with the outside edge being the east bank. Over time, the meander bend moved to the east, eroding the eastern bank, and imminently threatening homes within River’s Edge and another residential community to the north, Rio Vista. During major Brazos River flood events in 2015, 2016, and Hurricane Harvey in 2017, considerable portions of the east bank eroded and were within 120-feet of back property lines in River’s Edge. Additionally, the continued migration of the bank would threaten a flood protection berm the district had previously constructed along the bank to prevent floodwaters from reaching its residents from the north, leaving the district at a much higher risk for structure flooding. Based on local soils investigation, the line of repose (bank slope that would structurally stabilize the bank from further erosion) was within feet of residential backyards and into the flood protection berm.
Costello worked with MUD 140 to investigate and evaluate engineering solutions to protect the residents. We also identified and secured almost $9MM in grant funding from the National Resource Conservations Service (NRCS) Emergency Watershed Protection (EWP) program under the Federal Declared Disaster DR-4332 to help communities fund bank stabilization projects to protect structures. This funding allowed for the design and construction of the first streambank stabilization project along the Brazos River in Fort Bend County.
The United States Corps of Engineers (USACE) was preparing their Brazos River Flood Risk Management Study analysis with the USACE Engineering Research and Development Center (ERDC) while our team was researching and developing various design solutions to meet the goals and requirements of the EWP grant program and provide the needed protection to the district. Costello’s work was focused on protecting MUD 140, while ERDC’s study aimed to investigate all bank migration and erosion locations along the Brazos River within Fort Bend County, provide solutions for the major locations, and develop a comprehensive solution that could be employed to arrest the erosion.
At the time the grant was awarded to MUD 140 and Costello began investigating project design, the ERDC study was not finalized. Costello, Inc. coordinated extensively with ERDC on a range of possible solutions while we were identifying specific design solutions for MUD 140 and ERDC was evaluating solutions throughout the Brazos. Through this coordination, two alternatives were selected for further evaluation: the Palisade River Training System, which is a proprietary product of Er-Con, Inc., and Longitudinal Peak Stone Toe Protection (LPSTP). Both solutions allowed for fortifying the riverbank toe (bottom of the bank at the flowline of the river) and would induce deposition of silt along the areas of improvements, which over time would invite vegetation, further increasing the resiliency of the design.
The primary goal of either solution is to fortify the bank toe and not allow any continued migration (movement) of the toe towards the residential homes. Costello worked in association with ERDC to evaluate the remaining two design alternatives. The Palisade system is a lower-cost project, but there was a concern that due to the tight radius of this specific bend in the river, implementation of this method may induce erosion at other locations along the streambank. The LPSTP protection is a continuous, direct stabilization method that solidifies the protection at the toe of the riverbank, preventing the continued migration of the toe into the developed areas. A particular feature of the LPSTP is the peak stone which allows for “self-healing” as the river erodes at the base of the stone and permits the stone to launch, or fall, into the river, armoring the newly eroded area.
After extensive coordination and discussion between Costello, USACE, ERDC, NRCS, Fort Bend County, and MUD 140 Board of Directors, the LPSTP alternative was chosen for final design and construction for the MUD 140 site. There are no prior LPSTP projects that have been constructed within the Lower Brazos River. Additionally, the implementation of the peak stone design magnitude in size is unprecedented in the Lower Brazos River. The total stabilization limits were 3,125-linear feet and resulted in a total of 68,800 tons of 18-inch rip-rap.
ERDC’s Brazos River Flood Risk Management Study was released in March 2020 and identified 13 specific sites for future streambank stabilization projects along the Brazos River (see sidebar and figure). The River’s Edge Bend Streambank Protection Project is the only one of these sites designed to date, with construction completed in March 2021. The results of this project will serve as an example and pilot project, proving a concept that is untested under the conditions which exist in the Lower Brazos River for the development, design, and implementation of the additional future erosion protection measures identified. Fort Bend County Drainage District was highly involved in the development, design, and construction processes and is incorporating lessons learned into their overall plan for the County.
The ERDC staff provided expertise based on their experiences with other rivers in the United States with similar flow and soil conditions. The engineer’s probable cost estimate for the LPSTP of $8.18MM, which was within the award grant amount of $8.95MM.
The project bid price was $6.72MM, and the estimated construction timeframe was six months. As of March 9, 2021, the project was fully completed under the construction deadline and below the projected grant award amount.
Upon completion of the stabilization measures, spring rains kept the Brazos River at mid to top of bank flood levels for an extended time (March 2021 to July 2021) which are the conditions that loss of toe and bank erosion would occur. The flooding covered the main portion of the peak stone, not allowing for visual inspection during the high-water event. Upon the water receding, Costello performed an inspection to assess the functionality of the system. The main portion of the peak stone was as constructed. No lateral toe erosion was experienced, and silt was already deposited on the rip-rap, which is the first step toward full-bank re-establishment for vegetation and resiliency.
Preventing further migrations of the streambank provides extensive protection to existing residential structures along the bank protecting the residents and their investments. Unmitigated, the bank would have eroded into the homes and onto roads within MUD 140, impacting individual property owners and the water and sewer infrastructure for the district.
When evaluating the protection solutions, it was determined that either option would require environmental permitting with the USACE Galveston District due to the placement of fill below the ordinary high-water mark. Costello directed the environmental consultants (Bio-West) to evaluate both solutions and provide recommendations for permitting options. Both solutions were beyond the length limits of the Nationwide Permit (NWP), but the LPSTP was within the fill limitations. The Palisade option was outside the NWP limits because of the possible indirect impacts associated with the design. Both solutions required archeological and endangered species assessments, which resulted in relocating a protected mussel species and protecting a Native American burial ground that would have eroded into the river without the streambank stabilization. With the support of ERDC and NRCS, an NWP-37 was obtained with the Galveston District Colonel, providing an exception for this project for the overall length.
Once the LTSTP option was identified as the preferred alternative, the measures designed and constructed by Costello preserved the Native American burial ground as well as prevented additional impacts to the existing flood protection berm. Erosion impacts to this berm, would allow the Brazos River to flood the interior areas within MUD 140. As previously mentioned, the success of this project will provide confidence in future projects along the Lower Brazos, allowing for significant protection of critical infrastructure.
The project location itself, the Brazos River, was a challenge. The majority of the work was performed at the bottom of the river, which has a 50-ft high bank and limited to no access to the construction site. Additionally, work inside the Brazos Riverbank limits is highly regulated and environmentally sensitive. Most of the land where project construction occurred was not owned by the district. Extensive coordination and negotiations were required to obtain construction and permanent easements to execute the project. The hydraulics and condition of the soils created a complex design environment and led to many deliberations on solutions between the various regulatory agencies and engineers. The lack of other similar projects within the lower Brazos River further complicated the design, as there were no examples of success from which to learn. All design considerations and decisions occurred based on theoretical design conditions, not on practical application related to the Brazos.
When Costello initially identified and evaluated solutions to protect the residents of MUD 140, all reasonable protection options were not financially feasible for the district solely to fund. The preliminary solutions required additional upstream protections that were on lands not owned or controlled by the district. The solutions investigated included structural stabilization of the entire bank through the MUD 140 boundaries, sheet piling, Palisade River Training system, rip-rap protection, Longitudinal Peak Stone Toe Protection, bendway weirs, and bank regrading.
We continued to look for ways to help the district. Following Hurricane Harvey, Costello prepared an application for the National Resource Conservations Service (NRCS) Emergency Watershed Protection (EWP) grant program under the Federal Declared Disaster DR-4332, designed to help communities fund bank stabilization projects to protect structures.
Costello successfully aided the district residents by securing an $8.95 MM grant for this project, where the NRCS covers 90% of the construction cost and the district will cover the remaining 10%. Costello worked closely throughout the process with the MUD 140 board and NRCS in all project discussions and decision-making processes. The total project cost of $8.18 MM was under the award grant amount of $8.95 MM. This allowed the MUD board to sell infrastructure bonds to cover their share in accordance with the EWP contract.
Without the assistance of Costello and their desire to support MUD 140, this funding in excess of $8M would not have been available to help the district serve its residents and establish a benchmark for future streambank protection projects in the region.
The project fortifies and protects the toe, preventing further bank migration, which will ensure that the flood protection berm, residential structures, and lives will not be at future risk.
The Costello team successfully developed and secured funding for this complex, first of its kind project that the district would not have completed under normal circumstances. This streambank protection project provides security to the residents of the district that their homes are at much less risk of flooding, and they are less likely to lose the investment of their homestead to the Brazos River.