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Innovation: Royal Creek Channel Repair Study

INTRODUCTION

The City of Fort Worth requested that Freese and Nichols perform a feasibility study on Royal Creek to determine if the channel erosion in the study reach could be stabilized using natural channel design techniques. The City’s goals were to reduce erosion and “showcase” a natural channel design.

The City of Fort Worth had received complaints from residents along the creek about channel erosion and localized flooding, specifically about a failed concrete drop structure that resulted in a 13-foot vertical drop in the channel bed. 

Freese and Nichols conducted a stream geomorphic assessment where the entire study reach was walked, documenting channel conditions such as areas of instability, existing infrastructure, bed and bank sediment characteristics, knickpoints, bank failures, and density of vegetation cover. Hydrology and hydraulics (H&H) were modeled using HEC-HMS and HEC-RAS. The resulting data was used in conjunction with channel bed and bank sediment characteristics (sampled from the study reach) to estimate sediment transport potential and the equilibrium slope of the channel.

The results of the stream geomorphic assessment showed that a natural channel design was not feasible for the study reach of Royal Creek. The existing corridor width and limited access made for a poor location to design and construct a “showcase” project. Further, the channel was nearly stable and was experiencing only localized areas of bank erosion, primarily at the failed drop structure.

INNOVATIVE APPROACHES 

  • The sediment transport functions in HEC-RAS were used to generate a suite of stable channel dimensions that may be used for design in conjunction with the channel equilibrium slope. Site visit observations validated RAS sediment transport results.
    • Freese and Nichols studied the erodibility of the streambank soils using the submerged jet test.
    • The submerged jet test characterizes soil erodibility in the field. The jet test is simple, quick, relatively inexpensive to perform, repeatable and gives consistent results. The coefficients obtained from the test results were coupled with the H&H model data to predict erosion during different modeled storm events.
    • Submerged jet tests provided immediate results, instead of waiting for results of long-term erosion monitoring.
    • The erosion rates predicted using the submerged jet test were used to prioritize eroding streambanks throughout the reach. This will help the City develop capital improvement projects for bank stabilization or determine if continued monitoring is sufficient until funds become available.

BENEFITS

  • A natural channel design was not in the best interest of the City. Designing and constructing a natural channel for the study reach would have cost the City in excess of $500,000.
  • Freese and Nichols determined that the City should focus future efforts on stabilizing the failed drop structure. Design for this feature is moving forward using natural design techniques.
  • Freese and Nichols recommended long-term monitoring where streambank protection was not immediately needed.
  • Relatively inexpensive feasibility study resulted in savings for the City.

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