City planning channel improvement with $4.75 million loan to reduce flooding in Oso Creek
The City of Corpus Christi’s Public Works department is planning and designing channel improvements that will address flooding issues in the Oso Creek Basin through funding provided in a grant awarded by the Texas Water Development Board in 2022.
The TWDB award is a $4.7 million financial assistance loan through the Clean Water State Revolving Fund, one of numerous programs into which the Texas Legislature directed money in 2023 through the new Texas Water Fund to provide low-cost financing for planning, acquisition, design and construction of water, wastewater, reuse and stormwater infrastructure.
Entitled the Oso Creek Channel Bottom Rectification Project, the project is supported by $3,561,000 in financing and $1,190,000 in loan forgiveness for stormwater system improvements, along with a contingency fund of $344,754, with proposed improvements that would impact a 12-mile section of the creek.
The project scope includes preliminary designs to smooth the bottom of Oso Creek between Greenwood Road and Yorktown Boulevard, stabilize the banks to reduce the risk of contamination, contain large capacity runoff and convey flood water more quickly out of the urban area.
TWDB approved financing on the loan in January of 2022 during its first session of the year, which also includes loan forgiveness for qualifying disadvantaged and small and rural disadvantaged areas, emergency relief and green projects. The board estimated that the city could save $350,000 for the life of the loan through the fund in addition to loan forgiveness.
On March 26, the Corpus Christi City Council awarded a $4.2 million contract with Hanson Professional Services Inc. in Corpus Christi to begin design services to enhance the capacity of Oso Creek, leveraging fiscal year 2024 funding available from the loan.
Oso Creek is located entirely in Nueces County northeast of Robstown and runs about 28 miles southeast along Corpus Christi Bay to its mouth on the Cayo de Oso. The area is known among recreationists as a place for hiking the interconnected trails and watching for wildlife in the habitat ecosystem of Oso Bay. Cayo de Oso is also the site of one of the largest prehistoric cemeteries in Texas.
The creek is a natural stormwater conveyance that is subject to severe flash riverine flooding, which can result in stormwater and drainage issues. The Federal Emergency Management Agency proposed updates to outdated flood maps in 2018 showing that the area lies in a high-risk flood zone, underlining the exigent need to not only plan and design better stormwater systems with places to hold water, but ensure those plans are implemented properly.
Gabriel Hinojosa, assistant director of the Corpus Christi Public Works Department, noted that the city’s residents have been seeing more frequent and extreme rain events.
“Our creeks are what we call storage devices, because the water stores there until it can slowly run off to bays, creeks and receiving bodies,” he said. “We’ve had a lot more development in recent years, a lot more impervious cover and a lot more runoff.”
The loan won’t cover the cost of construction. Project leaders will look for other grant sources of funding to support shovel-ready projects for Oso Creek, which are estimated to begin in two to three years after they have completed planning and environmental permitting.
The estimated construction cost is about $45 million, which is about the same amount that the city submitted in a previous grant application to obtain Federal Emergency Management Agency loans through Community Development Block Mitigation (CDBG-MIT) grants for Oso Creek channel bottom rectification and bank stabilization to support flood control and mitigation measures. Known as the Hurricane Harvey Competition, that proposal also included a request for $26 million in funding to support an upgrade to Williams Ditch, a detention pond and other drainage improvements in the Tanglewood neighborhoods.
That grant defined a regional investment in risk reduction to develop natural storm infrastructure with sufficient design for flood conveyance and capacity. To address non-point pollution, the natural channel design will provide reduction in storm water pollution through preventing erosion and providing infiltration of runoff water into the soil.
Both Oso Creek and Oso Bay are listed as impaired waters in the most recent report from the Texas Commission on Environmental Quality, with high bacteria levels and depressed, dissolved oxygen in their waters.
The FEMA grant application's project activities for improved quality of urban runoff concentrated on reducing the risk of Oso Bay contamination specifically through reductions in Chlorophyll A, bacteria and algal blooms to maintain marine ecosystems and minimize adverse effects on public health and commercial and recreational fish harvesting.
Designated as an oyster harvesting area by the Texas Department of State Health Services, Cayo de Oso bacteria data was gathered through TCEQ's Total Maximum Daily Load Program to assess water quality for the FEMA grant. According to the grant application, nutrient and Chlorophyll A limits exceed TNRCC Water Quality screening criteria to such an extent that is considered normal. The large percentage of dissolved oxygen and pH concentrations accumulate in creek sediment, so that when the creek floods, it causes sediments to re-suspend and flush downstream and out into the Cayo de Oso.
While Oso Creek is defined as a mostly undeveloped area consisting of defined riverine channels with shallow, flat overbank areas, perennial flows and tidal streams, many local groups that test water quality recognize it as part of the greater ecosystem that can be impacted by stormwater runoff.
“Pollution from runoff can come to the sites through a variety of ways, flowing downstream from rivers as rain runoff, pasture manure, human or animal waste or damaged infrastructure, such as sewage lines,” said Tommy Shilts, Blue Water Task Force Coordinator for the Texas Coastal Bend Chapter of the Surfriders organization, a volunteer group that maintains a water quality monitoring program in partnership with Texas A&M University-Corpus Christi’s marine biology department to detect bacteria including Enterococcus and E.coli in water that would make it a threat to public health.
The TWDB loan establishes a commitment for all phases of the project, allowing program managers to plot the construction portion of the project to be ready to proceed before construction phase funds were released, and also to work in accord with the Stormwater Master Plan, a document that the city began working on in 2021 in partnership with Pape Dawson Engineers to develop a master plan for the city’s stormwater infrastructure, Hinojosa explained.
The FEMA grant application gathered data from an engineering analysis through the Hydrologic Modeling System (HEC-HMS) developed for the SMP to model existing conditions, 25-year interim buildout and ultimate development conditions on Oso Creek. The project was determined to benefit a population of 104,324 people living in the Oso Creek Basin service area and the entire 175.9-square-mile service area of the Oso Creek Stormwater Basin.
The SMP included an updated assessment of the city’s drainage infrastructure, with GIS data compiled and compared to as-built project data and formatted to be input into hydrologic and hydraulic (H&H) models for the Oso Creek watershed in Corpus Christi and outside of the city limits. Both 10-year and 100-year storm events were considered in evaluating infrastructure capacity and identifying areas with potential flood risk.
“The Stormwater Master Plan identified improvements that were needed for Oso Creek, though the creek was already at capacity with flooding,” Hinojosa said.
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This article originally appeared on Corpus Christi Caller Times: City designs channel improvement to Oso Creek with $4.75 million loan
