Corps proposes area flood study
Research would review burdened drainage system, changing climate
The U.S. Army Corps of Engineers is proposing a wide-ranging study of flooding in the Houston metropolitan area in response to the region’s devastating deluges, including Hurricane Harvey, an undertaking that could examine nearly every aspect of flood control, such as the city’s overburdened drainage system, a changing climate and the impact of paving over prairie and rural landscapes.
The first-of-its-kind study in the Houston area — called a Metropolitan Houston Regional Watershed Assessment — would examine 22 watersheds in the region, analyzing how stormwater moves from rooftops and streets to bayous and creeks, eventually to Galveston Bay, said Edmond Russo, deputy district engineer for Programs and Project Management for the Corps’ Galveston District.
The study would reexamine the “frequency, distribution and magnitude” of rainfall trends given recent years’ severe
weather and whether the Houston region’s development sprawl has had a “cumulative effect” on increasing flood risks downstream, Russo said.
‘A smarter plan’
The resulting report is expected to include proposals the Corps, state, Harris County Flood Control District or city could implement, ranging from new widening and deepening projects on area bayous to utilizing “green” infrastructure and incentivizing developers to use technologies such as “porous concrete” that are capable of absorbing floodwaters.
Big-ticket infrastructure improvements could then be eligible for federal investment by Congress or the Corps. For example, if the study identified a need for a $1 billion retrofit of the city’s drainage pipes and basins, the Corps could finance roughly two-thirds of that cost.
“You create a smarter plan with the regional watershed assessment,” Russo said. “What do we want to look at 10, 15, 20 years later in terms of sustainable flood risk management?”
The study would require congressional approval, cost at least $3 million and take approximately three years to complete. The disaster-relief bill passed by the U.S. House of Representatives in December, if OK’d by the Senate and signed by the president, authorizes the Corps to conduct two regional watershed assessments in disaster-affected regions, with priority given to areas with multiple disaster declarations in recent years.
The Houston region has had three major disaster declarations in the last three years, during the Memorial Day 2015, Tax Day 2016 and Harvey floods.
Russ Poppe, executive director of the Harris County Flood Control District, said while he supported the Corps effort, he was waiting to see the full scope of what the Corps specifically wants to study, which would be finalized after a congressional vote.
Poppe said the flood control district, for example, would like to see the Corps look at tributaries in addition to larger waterways the Corps traditionally has worked on.
The watershed study proposal comes as local officials continue to revamp flood control strategies in Harvey’s wake. The storm dropped more than 51 inches of rain in some parts of the Houston area, killing dozens and flooding hundreds of thousands of homes and other buildings.
Harvey shattered national rainfall records, in some cases exceeding the amount of rainfall believed to be scientifically possible.
Updated data
Harris County Judge Ed Emmett in October outlined a series of proposals in the storm’s wake, including mandating disclosure of flood risk to homebuyers and renters, buying out or elevating all homes in the 100-year floodplain and identifying where old waterways have been paved over by development to predict and prepare for releases from Addicks and Barker reservoirs.
Harris County Commissioners Court has indicated a willingness to put a bond issue before voters, possibly upward of $1 billion, to finance some improvements.
The National Oceanic and Atmospheric Administration currently is updating rainfall statistics. Preliminary data released in November suggested that current data routinely underestimate a “100-year” storm — rainfall that has a 1 percent chance of occurring in a given year — which could mean floodplain maps and regulations are falling short. The data would be finalized in May.
Harris County Commissioners Court also voted earlier this month to work with Montgomery County to re-evaluate flood risks in the San Jacinto River watershed, which could examine the feasibility of using Lake Conroe and Lake Houston for flood control purposes. For example, operators of the two reservoirs, which are designed to hold drinking water, could consider lowering water levels in advance of storms to make room for rainfall and prevent big releases.
Comprehensive strategy
If authorized by Congress, the Corps’ watershed study would be one of the most expansive developments following Harvey and would be the first to treat the network of waterways around Houston comprehensively. Where the Harris County Flood Control District would have the ability to make policy within only the county’s boundaries, the Corps could make recommendations and take on projects in the entire region.
It still would require cooperation from local entities. For example, as part of an examination of the city’s drainage system, the Corps would need data and schematics from the city.
“Obviously, we would like to help in whatever aspects that they would like to have information from us,” said Steve Costello, the city’s chief resilience officer, also known as the “flood czar.” “I don’t know the full scope of the work just yet. When I see that, I’ll be happy to expand on how much success we can get from that.”
Russo said the study’s scope could include evaluating whether the region’s sprawl is having a cumulative effect on downstream flooding, identifying “choke points” in city drainage systems and suggestions of ways to manage private water.
“Years and years ago, people used to have these large cisterns on their house that would collect rainwater,” Russo said. “Could you reintroduce the idea of a cistern to retain water and let it out slowly? What would be the cumulative effect of something like that?”
Are the solutions realistic?
If authorized, the Corps would try to work with NOAA on updating rainfall statistics, Russo said.
Larry Larson, senior policy adviser for the Association of State Floodplain Managers, said an expansive study based on watershed boundaries instead of political boundaries could be the right approach. The challenge, however, will be rallying the political entities to act on it.
“Makes a lot of sense,” Larson said. “Now the question is, when you come up with ideas and potential solutions, are they implementable?”