Design in a Time of Uncertainty
By Rives Taylor, Principal, Global Resilience Research Lead
Located 80 miles north of Houston on the Trinity River is Lake Livingston. Lake Livingston is the second-largest reservoir constructed for water supply purposes solely within the state. The reservoir is situated on the Trinity River which supplies more than half of Galveston Bay's freshwater inflows. It is an economic asset, drawing millions of visitors annually to the area for camping, fishing, and boating. for camping, fishing, and boating.
HARC and the U.S. Geological Survey (USGS) recently completed a Lake Livingston study for the Texas Commission on Environmental Quality (TCEQ)’s Galveston Bay Estuary Program, one of 28 National Estuary Programs. The purpose of the GBEP is to provide comprehensive ecosystem management through collaborative partnerships and to ensure the preservation of Galveston Bay's multiple uses. The Galveston Bay Plan is a comprehensive conservation and management plan for the Galveston Bay Estuary. The plan identifies freshwater inflows to the estuary as an essential management priority.
As freshwater flows from upstream watersheds to the Bay, it is vital to understand how sediments and nutrients move through the tributaries and reservoirs, and how this impacts sediment and nutrient loads in the Bay. The goal of this study was to determine if Lake Livingston traps sediments and nutrients as they move through the Trinity River system.
The completed report, entitled Impacts of Assimilative Capacity of Reservoirs, summarizes the assimilative capacity of the Lake Livingston reservoir and related impacts on freshwater inflows to the Galveston Bay estuary. In this context, assimilative capacity is the ability of the reservoir to absorb nutrient and sediment concentrations. As a technical partner, HARC worked with the USGS to establish site selection criteria and identify specific sampling locations.
HARC determined sampling design, including sample collection frequency, target flows, specific sampling procedures, and laboratory methods for water quality analyses. Conducted between May 2016 - August 2018, six water quality samplings occurred during the base, moderate, and high flow conditions.
The research team sampled inflow into Lake Livingston from the Upper Trinity River to the north and outflow into the Lower Trinity River south of the Lake Livingston Dam to quantify nutrient and suspended sediment concentrations. A GPS drifter was deployed to track flow patterns, currents, and collected depth profiles to determine the degree of stratification. The results of the sampling did not show elevated nutrient or sediment concentrations leaving the reservoir during the varying conditions.
The study results suggest that Lake Livingston is a nutrient and sediment sink. Most suspended sediments, phosphorus, and total nitrogen sample events resulted in a decreasing pattern from north to south. Overall, the sampling events do not show elevated nutrient or sediment concentrations leaving the reservoir during high or base flow conditions. That could be due to a lack of samples collected during high flow events, the time between sample collection, or turnover patterns in the reservoir. This study is limited by a lack of sample size and only one water quality sample collection during a high flow event. These early results suggest that as nutrients enter Lake Livingston, they assimilate into the reservoir.
The preparation of this report is available through funding grants from the TCEQ and the U.S. Environmental Protection Agency (EPA). For more information on the Galveston Bay Estuary Program, please visit their website.