Frequently Asked Questions - San Jacinto Regional Watershed

What is the San Jacinto Regional Watershed Master Drainage Plan?

The San Jacinto Regional Watershed Master Drainage Plan (SJMDP) is a comprehensive regional plan developed by local partners including the HCFCD, the SJRA, Montgomery County, and the City of Houston that identified and developed information for communities to use for hazard mitigation planning along the channels included in this study, including:

existing conditions flood hazard assessment,
analysis of historical storms,
data review and summary of information for sedimentation and vegetation management

primary and secondary flood mitigation measures

What information was developed during the study?

Information developed includes non-regulatory inundation maps (not intended to replace current FEMA effective Flood Insurance Rate Maps) for the studied streams that show the extent and depth of riverine flooding for the major streams within the watershed for an array of simulated storm events. Additionally, information was gathered about the number of structures, acres of land, properties, and miles of roadway as well as critical infrastructure and evacuation routes that are located within the inundated areas.

What is the purpose of the study?

The purpose of the SJMDP was to develop a comprehensive flood mitigation master drainage plan in the watershed. The study identified the watershed’s vulnerability to flood hazard, developed approaches to enhancing public information and flood level assessment capabilities, and recommended flood mitigation strategies for both the near and long-term.

What is the study area?

The study area covers approximately 2,900 square miles, located in seven different counties. The SJMDP includes approximately 535 miles of stream, including West Fork San Jacinto River, East Fork San Jacinto River, San Jacinto River, Lake Creek, Cypress Creek, Little Cypress Creek, Spring Creek, Willow Creek, Caney Creek, Peach Creek, Luce Bayou, Tarkington Bayou, and Jackson Bayou.

How is the study funded?

The SJMDP is funded jointly at 75 percent by the FEMA Hazard Mitigation Planning Program, conveyed through the Texas Division of Emergency Management, and 25 percent by the four local partners: the HCFCD, the SJRA, Montgomery County, and the City of Houston.

What is the Spring Creek Siting Study?

The Spring Creek Detention Siting Study is being conducted in parallel with the SJMDP and is funded by the HCFCD and several Municipal Utility Districts (MUDs) within the Woodlands, including MUD1, MUD7, MUD46, MUD60, and MUD386. The purpose of the study is to evaluate additional alternative detention sites within the Spring Creek subwatershed and incorporate them into the SJMDP. The study team evaluated a total of twelve detention alternatives in the Spring Creek subwatershed, two of which are recommended for implementation in the SJMDP (Walnut Creek Dam and Birch Creek Dam).

What are the primary sources of flooding in the San Jacinto River Watershed?

There are two primary sources of flooding in the San Jacinto River Watershed: riverine flooding and neighborhood drainage system flooding. Other sources of flooding are sheet flow and lake flooding.

Riverine flooding occurs when a river or channel overflows its banks. Riverine flooding can be a result of both intense bursts of rainfall and long duration rainfall events. Road crossings that are undersized or clogged with debris can also contribute to river flooding. Rivers also flow into lakes which can cause flooding.
Neighborhood drainage systems include infrastructure such as roadside ditches and storm sewers that carry runoff that ends up in nearby channels or collecting bodies of water (the receiving channel). Intense rainfall that exceeds the capacity of the neighborhood drainage systems can surcharge or back up and cause flooding even when the receiving channel is not flowing full. Proper drainage criteria standards can reduce the chance of neighborhood drainage systems being overwhelmed. At times, the receiving water body, such as a downstream river or lake, may back up into the drainage system and cause flooding.
Sheet flow is the movement of shallow runoff across the ground during a rainfall event as the runoff makes its way to the drainage system or river. Natural sheet flow patterns can be altered by development causing some areas to flood that did not before.

The San Jac study focuses on resolving riverine flooding impacts. Other studies are ongoing by HCFCD and others to address flooding along neighborhood drainage systems.

How can I provide feedback on the study?

Though the SJMDP study portion is scheduled to conclude in the Fall of 2020, comments are welcomed for the continuation of the study. For more information about the study and to provide comments, or to join the mailing list, visit www.23.102.189.58 and www.23.102.189.58/contact-us/.

What is a Hazard Mitigation Plan?

A Hazard Mitigation Plan is a document that identifies hazards and develops long-term strategies to reduce the impacts of disasters, such as flooding. Governmental organizations engage in hazard mitigation planning to identify risks and vulnerabilities associated with natural disasters and develop long-term strategies for protecting people and property. Mitigation plans are key to breaking the cycle of disaster damage, reconstruction, and repeated damage. The Hazard Mitigation Plans can be updated with the projects recommended in in the SJMDP.

What is Atlas 14 rainfall data?

NOAA Atlas 14 is a peer-reviewed publication that serves as the official government source of precipitation frequency values for the United States. NOAA Atlas 14 rainfall data is used for infrastructure design and planning activities under federal, state, and local regulations. The data is also used to help delineate flood risks, manage development in floodplains for FEMA’s National Flood Insurance Program and are used to monitor precipitation observations and forecasts that can indicate flooding threats by NOAA’s National Weather Service. The most recent Atlas 14 publication for this region, Volume 11, was released in September 2018 and showed significant increases in rainfall depths compared to previous studies.

What is hydrologic and hydraulic analysis and modeling?

Hydrologic and hydraulic analysis and modeling are the tools engineers use to simulate natural rain events to predict the runoff response of the watershed to better understand how stormwater is collected and drains downstream. Using hydrologic and hydraulic data from the U.S. Geological Survey, FEMA, and organizations like the HCFCD, engineers can utilize an integrated system of software to simulate real‑world conditions in our region’s bayous, streams, and channels. These simulations are completed using hydrologic and hydraulic, or H&H, models. These models predict how precipitation will impact the landscape with estimates of how deep the water will get at different locations and how frequently this water depth will occur under certain weather conditions. Other models are used to estimate the monetary damages that can be expected when these events occur in developed areas and damage property.

Hydrology is the scientific study of the water cycle. It involves analyzing rainfall, soils, land use, and topographic data to calculate the amount of rainfall that enters rivers, channels, and drainage systems.
Hydraulics is the study of water moving through conveyance systems. It involves analyzing the carrying capacity of the drainage system to calculate velocity, flood depths, and flood extents.

How will the projects in the San Jacinto Regional Master Drainage Plan be funded?

As projects move forward, there may be opportunities to leverage multiple funding sources, including through federal and state grant programs. The study team will consider various funding sources. Each grant program may have differing procurement, administrative, and environmental requirements. Evaluation of funding opportunities and applications for specific grants or other sources will be conducted during implementation planning. Another option is to fund projects through local sources. These could include local tax revenue, bond funding, special purpose districts, or other mechanisms. Given the estimated costs of these projects, partnerships among the local jurisdictions who benefit are recommended.

How were projects in the San Jacinto Regional Master Drainage Plan ranked?

The study partners evaluated several metrics to be considered in the ranking of the projects. The metrics considered are as follows: historical damages, predicted damages, the reduction in structural flooding instances over a 50-year period, the number of structures with reduced flood risk during the 1 percent ACE storm, the benefit–to–cost ratio of the project, the improvement to roadway mobility, benefits to socially vulnerable areas, benefits to low-to-moderate income areas, and project cost.

What are the identified short-term measures (Additional studies, recommended policy changes, etc.)?

Vision Group – This group would establish a regional entity across county boundaries for continuing to cast a vision for regional project implementation and common drainage criteria throughout the watershed. The group could foster collaboration to evaluate the path forward in reducing vulnerabilities to flood hazards and improve resiliency. The Regional Flood Planning Group that is being formed as part of the State Flood Plan process would be the ideal candidate.
Policy – While each entity may not need identical drainage criteria, common base criteria would standardize the minimum requirements needed for future development. Policies that could be standardized include detention methodology, and hydraulic methodology, floodplain analysis, and minimum finished floor elevations.
Floodplain Preservation/Conservation Areas – Identify areas along major streams that could be set aside as conservancy areas to preserve the floodplain and prevent increase in flood risk.

Flood Monitoring/Warning Enhancements – Adding rainfall and water surface elevation gages to provide both the emergency managers and the public with additional information to determine flood risk.
Flood Response – Improve flood response by enhancing communication, identifying and prioritizing improvements to critical infrastructure in flood prone areas, and developing public education strategies.
Buyouts – Acquiring property and removing it from potential flood risk is often the most cost-effective approach. There are over 600 structures identified within the 20 percent ACE (5-year) floodplain at an anticipated buyout cost of $190 million. The counties and regional groups should seek funding to develop a buyout program for these frequently flooded structures.
Floodplain Re-Mapping – The updated modeling for the existing flood hazard assessment showed that current elevations and floodplains used within the watershed are outdated. The average 1 percent ACE (100-year) water surface elevation increased between 0.5 and 4.5 feet in the watershed, meaning structures built to current standards could still be within the 1 percent ACE and are more susceptible to flooding. Re-mapping the watershed would provide updated flood risk information to agencies and the public.
Watershed Protection Studies – Watershed protection studies for each of the watersheds would further analyze the flooding potential on the tributaries of the major streams and identify local drainage improvements needed. The recommended study prioritization begins with Spring Creek, followed by the West Fork, Caney Creek, Peach Creek, Lake Creek, Luce Bayou, and the East Fork.

What are the identified long-term measures (Structural measures)?

Long–term measures consist of the recommended projects which will take longer than five years before implementation due to funding, environmental permitting, construction time, and project constraints. These projects consist of structural solutions, including:

Stormwater detention basins are excavated man–made impoundments (dry dams) that capture runoff, detain it, and release at a slower flow rate. The result is lower water surface elevations downstream. Each detention facility was conceptually designed to provide flood damage reduction benefits along the major study area streams.
Channel conveyance improvements consist of excavating channels to allow for more capacity of flow thereby reducing the water surface elevations in the immediate project area. Channel conveyance improvements can range from concrete-lined sections, to man-made channels that incorporate environmentally friendly features.

What policy recommendations are included in the San Jacinto Regional Master Drainage Plan?

The study team recommends that local jurisdictions consider adopting and implementing the following:

Requiring detention for new development and for capital improvements projects that increase conveyance,
Requiring drainage analyses for development and capital improvement projects that demonstrate no adverse impact,

Requiring analyses be performed for multiple storm events ranging from frequent to infrequent to ensure sufficient detention is provided to prevent impacts,
Using common criteria when analyzing detention and floodplain analysis being mindful that runoff does not consider political boundaries,
Implementing consistent policies that encourage limiting development in the floodplain,
Acquiring floodplain property when it is available, including through buyout programs, and
Requiring that losses to floodplain storage be mitigated and that adverse impacts are avoided.

Why are there no planned projects in the Cypress Creek Watershed?

The San Jac study considered flood reduction improvements across the region that can provide benefits in both the project watershed as well as further downstream. Many of the watersheds have no current planning study in place to address these issues. Cypress Creek already has a number of studies that have been completed as well as several flood reduction projects that are identified. There have been extensive studies at the upper end of the watershed conducted by the Harris County Flood Control District and the US Army Corps of Engineers in relation to the “Third Reservoir”. While this project could provide significant benefit to the western portion of Harris County by reducing or eliminating the overflow into the Addicks watershed, it would not provide benefits downstream of the overflow and toward Lake Houston. Other study efforts along Cypress Creek include a recently completed retention study, an active watershed planning study, and others that have documented flooding and recommended both short-term and long-term projects. 

The Regional Drainage Plan and Environmental Investigation for Major Tributaries in the Cypress Creek Watershed (K100-00-00) was completed in February 2020. The goal of this work was to identify projects to reduce or eliminate existing flooding risks in the Cypress Creek watershed. As funding allows, individual recommendations from this study will proceed to right-of-way acquisition, environmental investigation, and preliminary engineering. The three projects in this scope of work included:

An update to the 2003 Texas Water Development Board “Regional Drainage Plan and Environmental Investigation for Major Tributaries in the Cypress Creek Watershed,” Bond Project CI-035. This study update identified options to reduce existing flooding risks in the Cypress Creek watershed. During the course of the investigation, the scope of work was expanded to include the investigation of additional potential detention sites along the main stem of Cypress Creek and of flooding issues related to bridge crossings along Cypress Creek.

An investigation of the potential benefit of expanding Cypress Park Stormwater Detention Basin, HCFCD Unit K500-01-00 (formerly Bond Project CI-36.) This basin is located on North Eldridge Parkway near the confluence of Little Cypress Creek and Cypress Creek.
An investigation of the potential benefit of possible stormwater detention sites near Cypress Creek and Stuebner Airline Road (formerly Bond Project CI-020.)

In August 2018, Harris County voters approved a $2.5 billion bond program for flood risk reduction projects. This includes more than $291 million in projects for the Cypress Creek watershed, all of which have been initiated and are now in various stages of development. Other efforts in the watershed include the Little Cypress Creek Frontier Program. This is one component of the Harris County Flood Control District’s overall Frontier Program, which is an organized effort to plan for regional drainage infrastructure in advance of future land development. The Little Cypress Creek Frontier Program includes multiple projects in the watershed, including nine stormwater detention basins and stormwater conveyance improvements along Little Cypress Creek and its tributaries. The program will be funded under several Bond IDs included in the 2018 HCFCD Bond Program. Given all the ongoing efforts in the Cypress Creek and Little Cypress Creek watersheds to address flooding issues, the study team felt it was important to focus on areas where more planning is needed to work toward reducing flooding in the larger San Jacinto River Watershed.

What are the next steps recommended for the region and stakeholders?

Submitting this study to the new Regional Flood Planning Group (RFPG) led by the Texas Water Development Board to set both short–term and long–term goals for inclusion in the Texas State Flood Plan.

Identifying a Regional Facilitator as part of the RFPG to coordinate flood mitigation projects, policy, and procedures.
Coordination among the study partners and other stakeholders to develop common drainage criteria for hydrology, detention, and floodplain analysis.
Installing rainfall, stage, and discharge gages to enhance the existing flood warning capabilities.
Continuing a coordinated response among emergency managers during flood events and implementing the recommended improvements for communication, flood monitoring, and public education.
Continue to buy out structures that are repeatedly flooded.

Re-mapping the floodplain within the basin for Atlas 14 rainfall consistency and accuracy of existing flood hazards.
Developing watershed protection studies for the tributaries into the major streams to identify the flood risk and assess potential flood mitigation strategies.