Mother Nature knows how to keep high water at bay

A fraction of earth — a mere 9 percent — of the 4.8 million acres of land that make up the eight counties of the Houston-Harris County region are protected, areas that have been set aside to detain floodwater, provide recreation for people and habitat for wildlife, maintain native vegetation for erosion control and preserve flood-mitigating natural waterways.

But to do all its many jobs well, this “naturebased infrastructure” requires maintenance. In response to Hurricane Harvey, Harris County Judge Ed Emmett developed a 15-point plan to reduce the worst effects of the next flood event. Along the same lines, the regional business community put together its own Harris Plus Flood Solutions plan. Both propose to restore the dams and detention areas of Addicks and Barker reservoirs to first-class condition, including removal of sediment and invasive species that have accumulated since the structures were first built.

In the complex system developed to keep water at bay in our flood-prone area, the U.S. Army Corps of Engineers owns, operates and maintains the two reservoirs, including the operation of outlet gates that control water discharge into Buffalo Bayou. For its part, the Harris County Flood Control District devises and implements flood damage reduction projects and assists with maintenance of the channels that flow into and out of the reservoirs. This system was designed to hold more rainfall than a 1 percent rain (or 100year flood) event.

But the aftermath of Hurricane Harvey has exposed structural and ecological weaknesses inside the 26,000 acres of the two reservoirs, including years of silt and sediment buildup from upstream water flow, invasive trees and non-native grasses that have out-competed native species and feral hogs that have destroyed

functionally crucial vegetation. What’s more, the reservoirs are home to exotic armored catfish that burrow into and destabilize stream banks, causing more erosion and sedimentation. The result is that the reservoirs no longer hold and absorb water at original capacity, and they can’t effectively clean flowing water, prevent erosion, improve air quality or provide enhanced wildlife habitat and recreational space.

To restore these important functions, we must understand the role that “restorative maintenance” plays in our waterway-based region, make funds available to pay for restoration and for regular cleanup. In addition, the benefit-to-cost ratio of maintaining naturebased land use can be substantially greater than maintaining “gray infrastructure” equivalents (sewers, culverts, wastewater treatment and the like).

If the Army Corps and county flood control are to implement reservoir recovery plans in a way that is both costeffective and ecologically beneficial they must:

Remove years of silt and sediment build up in the upstream channels, in both reservoirs and downstream, and use it along bayous and streams severely eroded during Harvey. Harris County Flood Control has begun assessing channels and de-silting where needed to restore capacity to original design. Silt and sediment removed along Buffalo Bayou can provide material for rebuilding in high-erosion areas if a plan existed to do so.

Replace the non-native trees and exotic woody and herbaceous plants and grasses that have invaded Addicks and Barker reservoirs with native species to reestablish what had historically been a healthy coastal prairie ecosystem.

Enhance and maintain the upstream channels leading into the reservoirs to mitigate pressure on reservoir capacity and the system of bayous and banks downstream, which would both enhance green spaces and improve flood control.

Excavate Addicks and Barker reservoirs. Harris County and the Corps of Engineers should partner to excavate the reservoirs so that as much water as possible is stored exclusively on government-owned land. The Corps is working with the county and other stakeholders to fund a study for this purpose. In the meantime, regional officials need not wait for federal funding to start on many of the nature-based infrastructure improvement projects, which would speed completion of needed flood mitigation measures.

Even as counties await federal and state funding for needed flood control, this region could undertake “restorative maintenance” projects adjacent to the reservoirs to repair ecological functions, increase floodwater retention capacity and create new community assets for outdoor recreation. Maintaining the 9 percent of preserved and protected nature-based infrastructure in our region, including the Addicks and Barker reservoirs and their tributaries, is a critical piece of the multi-project plans to make Houston stronger and more resilient.