Flood risk does not stop at a county line. Neither should the planning, modeling and infrastructure investments used to manage it.
That is the message that guided our August 20 forum, Understanding the Impacts of MAAPNext. The discussion brought together Russ Poppe, Fort Bend County Drainage District, and Ross McCall, Waller County Engineer. Steve Costello, Vice President at Carollo Engineers and Houston’s former Chief Resilience Officer, moderated the conversation.
While MAAPNext is a Harris County initiative, the forum focused on what its improved modeling and flood-risk information mean for adjoining counties experiencing rapid development. Fort Bend and Waller counties share watersheds with Harris County, and decisions made in one jurisdiction can affect communities, infrastructure and investment across the region.
MAAPNext as a Regional Catalyst
MAAPNext is developing more comprehensive flood-hazard information for Harris County using Atlas 14 rainfall data, current terrain information and more advanced modeling. Although those maps do not automatically establish regulations outside Harris County, Poppe described the initiative as an important regional catalyst.
Harris County’s size and resources allowed the Harris County Flood Control District to advance an innovative modeling effort that smaller neighboring jurisdictions might not have been able to undertake independently. Fort Bend County has benefited from that work while updating its own drainage criteria and watershed master plans.
Poppe noted that Fort Bend County’s previous master planning and criteria dated back several decades. MAAPNext helped bring the county into a broader conversation about how flood-risk information and development standards should respond to rapid growth.
McCall described Waller County as being at an earlier stage, with fewer staff and financial resources. However, the county can learn from the experience of Harris and Fort Bend counties rather than building its approach from scratch. Waller County is currently developing six hydrologic and hydraulic models using methods similar to those employed through MAAPNext, including two-dimensional rain-on-mesh modeling. The county expects to finalize the models soon and then seek their acceptance by Commissioners Court as best available data.
“We do have the authority, but really, we have the responsibility for a regional approach,” McCall said. That responsibility includes building relationships with neighboring counties and developing the internal capacity needed to manage increasingly complex drainage questions.
When Watersheds Cross Political Boundaries
Differences among county maps, models and regulations create practical challenges for developers and engineers working near jurisdictional boundaries.
Both panelists encouraged project teams to engage public agencies early, especially when a property or watershed involves more than one jurisdiction. In those circumstances, the most conservative applicable assumptions or standards may provide the safest starting point. Early coordination can also prevent a project from advancing under one set of expectations only to encounter a significantly different analysis later.
Fort Bend County has incorporated many elements of Harris County’s approach, including coupled one-dimensional and two-dimensional watershed models. However, Poppe cautioned that neighboring counties should not simply copy Harris County’s criteria word for word. Soil conditions, infiltration rates, land use and other local factors can vary. Regional consistency is valuable, but the modeling must still reflect conditions on the ground.
Fort Bend County is also in discussions with Harris County Precinct 4 for coordination along their shared boundary. These conversations illustrate how neighboring jurisdictions can move from informal communication toward clearer processes for reviewing development and managing shared drainage systems.
Effective Maps and Best Available Data
One of the most important issues for the development community is the distinction between effective FEMA maps and newer best available data.
Fort Bend County’s effective FEMA maps predate Atlas 14. For federal flood insurance and certain map-revision processes, those maps remain the official reference. For local drainage impact analyses and development reviews, however, Fort Bend County uses its newer Atlas 14-based floodplain information.
This creates what Poppe called a “two-model situation.” A developer who looks only at the effective FEMA map may conclude that a property is outside the floodplain, only to learn during engineering review that current modeling identifies additional flood exposure.
Poppe strongly encouraged developers and consultants to review Fort Bend County’s best available data at the beginning of a project. The county hopes to update its criteria and master plans and eventually resolve the two-model system, potentially with support through the Texas Water Development Board’s Flood Infrastructure Fund.
Waller County anticipates confronting a similar issue once its six new models are completed and accepted. The FEMA maps will remain official until formally updated, but the county may use the new models as the best available information for local regulation and development review.
Defining “No Adverse Impact”
Fort Bend County applies a no-adverse-impact approach to development. In principle, when a project is completed, it should not worsen hydraulic conditions or transfer additional flood risk downstream.
New two-dimensional models provide a much more detailed picture of how water moves across the landscape than older one-dimensional channel models. That additional detail is valuable, but it also creates questions about what constitutes a meaningful impact.
A model may identify very small changes in water-surface elevation across numerous grid cells. The panel questioned whether every modeled change should be treated as an adverse impact, particularly when the result may be smaller than the margin of uncertainty in the underlying data.
Costello emphasized the need for engineering judgment and practicality. Public agencies must protect health, safety and property without allowing negligible modeled differences to create unnecessary delays or disputes. Developing a consistent regional understanding of what constitutes a meaningful impact will become increasingly important as more jurisdictions adopt two-dimensional modeling.
Measuring What Happens on the Ground
Models are essential, but the panel also emphasized the value of real-world measurements.
Fort Bend County is working with the Harris County Flood Control District to expand the regional network of rainfall and stream gauges. The county added 13 gauges last year and expects to add a similar number this year, including gauges in undeveloped areas.
Establishing baseline information before those watersheds are built out will allow officials to compare modeled assumptions with actual conditions. Over time, the data can help determine whether drainage criteria and mitigation requirements are working as intended.
Fort Bend County is also exploring how more of Harris County’s Flood Warning System functionality could extend across the county line. Features such as watershed boundaries, stream centerlines and inundation information currently become more limited outside Harris County, even though the waterways themselves continue across the region.
Planning Infrastructure Before Growth Arrives
Rapid development is placing additional pressure on drainage systems that were built for rural or agricultural conditions.
McCall compared Waller County’s planned drainage network to a major thoroughfare plan. By identifying ultimate outfalls, channel needs and future rights-of-way before full buildout, the county can communicate long-term requirements to developers and preserve critical drainage corridors.
Poppe described similar challenges in western Fort Bend County, where major industrial projects may discharge into shallow agricultural channels with limited capacity. Developers can respond with larger detention basins or pumped systems, but those requirements may consume so much land that a project no longer works economically.
The answer cannot always be to require an individual development to solve a regional infrastructure problem alone. Fort Bend County is examining impact fees and other financing tools that could help create drainage capacity while distributing costs more appropriately. Poppe emphasized that this infrastructure is essential to attracting the industrial development and employment centers county leaders want.
The closing discussion called for greater state investment in flood damage reduction infrastructure and for preserving local tools such as impact fees and tax increment reinvestment zones. Without those resources, counties may struggle to keep pace with growth and serve as effective partners to the development community.
Toward a Unified Regional Approach
Looking ahead, Poppe challenged the region to consider whether technology now makes a unified watershed model possible. Instead of separate models ending at county boundaries, jurisdictions could potentially work from a shared model covering a waterway from its upstream reaches through Fort Bend, Waller and Harris counties.
Such a system could improve consistency, help evaluate cumulative impacts and give developers a clearer understanding of expectations. Achieving it would require technical cooperation, political support and state funding, but the concept reflects the larger lesson of the forum.
MAAPNext is about more than new lines on a Harris County map. It is an opportunity to strengthen regional relationships, modernize planning and ensure that flood infrastructure supports both public safety and quality growth. For Greater West Houston, the work ahead is not simply to develop better models, but to use them together.