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Tuesday, January 7, 2014

Coastal ecosystem work led to concerns about new reservoirs


Impact of reservoirs on Galveston Bay and estuaries along Texas coast

Surface-water reservoirs’ evaporative water losses aren’t the only reason that HARC President Jim Lester has been speaking out against over-reliance on such projects to meet Texas’ future water needs as the State Water Plan is implemented.

As Lester’s and other HARC scientists’ longstanding scientific involvement with coastal ecosystem issues has underscored, reservoirs can bring lasting environmental harm. Those impacts occur both in the immediate area where reservoirs are constructed along rivers and in the wildlife-rich bays and estuaries that those rivers nourish along the Texas coast.

Preventing that environmental damage at the same time that reservoir evaporation is avoided makes more sense to Lester. His recommendation – substituting underground water storage for some new reservoirs – is also in line with HARC’s mission of helping people thrive and helping nature flourish at the same time.

If Texas keeps damming rivers to meet its water needs, evaporation from reservoirs may reduce the hoped-for benefits. Meanwhile, those reservoirs may further reduce nutrients flowing into bays.

--Jim Lester

Lester’s recent public comments on the State Water Plan in interviews with reporters and a newspaper column have their roots in HARC’s continuing focus on coastal subjects, particularly around the Galveston Bay system.

“Texas has built so many reservoirs that have basically put the coast on a diet” in terms of the nutrients that rivers provide to bay ecosystems, he said. Bays and estuaries function as invaluable homes and nurseries for numerous coastal, marine and migrating wildlife species.

Every dam built in Texas reduces the volume of nutrients that flow downstream while trapping sediments that are part of the geological process that creates crucial natural formations such as deltas, estuaries and sandbars, he added.

Dam-blocked nutrients that formerly nourished coastal wildlife now feed the sport-fishing species such as Florida largemouth bass that have been stocked in the lakes created behind those dams.

Texas dams have been so effective at reducing nutrient flows to bays in the state that the excessively high levels of nutrients that damaged other coastal ecosystems such as Chesapeake Bay on the Atlantic Coast have never widely materialized in Texas, Lester said.

The coastal region fed by the Brazos River is the only one in Texas with a high-nutrient problem because there are no dams on that river near the coast, he said. By contrast, the Trinity River, a Galveston Bay tributary, has much lower nutrient levels below Lake Livingston than it does above the dam that created that reservoir.

Lester has served as an editor of two editions of “The State of the Bay,” a scientific report summarizing and assessing research findings about environmental trends in the Galveston Bay system. He is also currently vice-chair of the Trinity and San Jacinto Rivers and Galveston Bay Basin and Bay Expert Science Team, which advises state officials on how to manage flows in those rivers for the benefit of the organisms in those rivers and in the bay.

The Trinity-San Jacinto team’s recommendations were not as wildlife-friendly, in Lester’s opinion, as those produced by science teams for other rivers. He attributes the difference to the Trinity-San Jacinto team’s inclusion of engineers who work for the agencies that manage dams on those rivers along with wildlife biologists.

It was his experience on the Trinity-San Jacinto team that inspired Lester’s growing attention to the State Water Plan’s strong emphasis on building new reservoirs to serve future water needs in Texas.

Voters’ approval of funding for new reservoir proposals in the State Water Plan poses a dual concern, he explained: If Texas keeps damming rivers to meet its water needs, evaporation from reservoirs may reduce the hoped-for benefits. Meanwhile, those reservoirs may further reduce nutrients flowing into bays.

Some proposed reservoirs would also flood valuable riverside ecosystems, and Texas is “short on those good bottomland forests” already, because development has expanded into once-forested areas near rivers, he added.