As its population booms, one of Texas’ most pressing needs is to develop water management strategies that meet current and projected demand. Ron Cass explores several viable alternatives.
Despite recent torrential rainfall, drought remains a persistent concern in Texas. From 2009 through 2014, recurrent droughts were more damaging than even the historic droughts endured in the 1950s.
Many Texans remember 2011, the worst drought year in state history. Cities were scrounging for solutions while enacting burn bans and water restrictions. Landscape irrigation was prohibited in some regions, and many municipalities and industries were at risk of losing their water sources as rivers, lakes and reservoirs fell below the level of the intake.
To make water systems more resilient, projects were implemented on an emergency basis to provide alternate raw water supplies, lower lake and river intakes, and develop direct and indirect potable reuse alternatives. These investments have proved valuable in armoring against future drought conditions.
The effects of unpredictable weather patterns are not the only challenges to consistent water supplies. The population of Texas is anticipated to grow from just over the current count of 28 million people to more than 46 million by 2060. With increased demand, water sustainability becomes a more pressing issue. The good news is there are solutions, and each offers an opportunity to strengthen water supplies through diversity.
Six key alternative water sources
Here are six alternatives that sequentially decrease in cost although also offer diminishing returns in the water supply’s reliability.
1. Seawater desalination. The Gulf of Mexico has long been considered an abundant water supply, but one that would only be used as a last resort. Challenges include permits, brine disposal, time required to finance and build, high power costs, and extending treated water to high-demand areas, which are often far from the coast. The primary objection to implementing a seawater desalination plant is usually cost. It’s while treating seawater costs more compared to treating surface water, reuse water and brackish ground water, it’s also the most secure.
Seawater intakes, outfalls and finished water distribution drive the cost variability of these desalination projects. Emerging membrane technologies and material advancements are expected to provide significant energy savings and productivity in the coming years.
2. Brackish water desalination treatment has been used for decades in Florida. The application of reverse osmosis (RO) and nanofiltration to reduce salinity and total dissolved solids (TDS) in groundwater is being used more frequently inland. The availability and reliability of surface water increases interest in groundwater availability. With most potable quality groundwater already allocated, the remaining can offer poorer quality with high TDS, high hardness or brackish salinity levels. When groundwater quality is poor, use of RO for salinity and TDS or nanofiltration for high hardness are common solutions.
3. Potable reuse. Applications for direct potable reuse (DPR) and indirect potable reuse (IPR) are increasing around the globe, but there are still obstacles associated with public perception of the water’s quality and reliability. Treatment processes can be made more reliable through online, real-time monitoring of potable reuse as it’s processed. In the past two decades, monitoring tools have made significant advances by combining online analyzers, real time data, historic data logging and process algorithms to enhance treatment process control. Predictive analytics are being used in complex projects to identify departures from expected operation and recommend operator responses.
In the Austin, Texas suburb of Buda, DPR was considered as one of several water supply strategies. Currently, 40 percent of the City of Buda’s available water supply is from city-owned groundwater wells and 60 percent is treated surface water. AECOM performed a DPR feasibility study of Buda’s wastewater treatment plant that led to an effluent characterization study as the next step toward confirming the viability of DPR as an alternative water source. The effluent characterization study was completed in March 2018 and Buda officials are evaluating whether to proceed further with DPR.
The Buda DPR study and an additional DPR feasibility study for Alliance Water (comprising Buda and the neighboring cities of Kyle, San Marcos and the Canyon Regional Water Authority) advanced the understanding of approaches to implementing DPR in inland regions where RO concentrate disposal options are limited.
4. Aquifer storage recovery (ASR) is not technically a source of water — aquifers function more like a bank, naturally holding water in underground layers of rock. Aquifers provide operational flexibility to store vast amounts of water without the risk of evaporation in hot weather. When water is abundant and readily available, it can be injected into an aquifer and then, when demand is high, extracted as a raw water supply supplement. While evaporative water losses are not an issue for ASRs like they are for surface reservoirs, full return of water stored in aquifers is unlikely due to groundwater movement. Additionally, this approach is very much location dependent, requiring knowledge of the subsurface geology and aquifer’s nature.
5. Surface water is the most common water source for potable water treatment, but it’s also the most unreliable due to continued climate extremes. While rivers, lakes and reservoirs are dependable sources during normal weather conditions, the next severe drought reminds us of the unreliability of these supplies.
Climatic changes continue to impact our ability to make reliable predictions on calculable surface water availability. While permits are issued on available science, certain components of surface water availability remain unpredictable. A resilient water supply portfolio includes a variety of resources, some that are less and some that are more dependent on climate and weather conditions.
6. Ground water is easily the most affordable water available — so long as there is ready access to it. While ground water remains an acceptable alternative source, the question is always, for how long? During heavy drought periods, aquifer levels typically decline across Texas. While pumps can be lowered as water demands increase, the rate at which ground water supplies recharge can vary widely. Some regions exceed their aquifer yield, withdrawing so much water that the land could sink and settle, limiting future aquifer storage capabilities. It’s also worth noting that the price of this water source varies depending on aquifer characteristics.
Today, AECOM is managing large-scale programs to convert from ground water to surface water in areas like Harris County. The 1975 formation of the Harris-Galveston Coastal Subsidence District was driven by Houston’s growing population and its downward-shifting coastline. Unchecked withdrawal from groundwater sources created a risk to property, while the depleted water supply would constrain industry, business and population growth. Houston looked to reduce its need for ground water through pioneering programs including:
• Additional surface allocations such as Lake Conroe, Lake Livingston and Luce Bayou Interbasin Transfer
• Storage of raw water, when available, at Allen’s Creek Reservoir
• Surface water treatment expansion at the Northeast Water Purification Plant
• Transmission of potable water to demand, beginning in 1985 and continuing through 2025
Which alternative water source is the best?
Each option offers distinct benefits and cost impacts. Rather than considering just one source, a diversified portfolio of water source solutions is the best way to minimize risk and protect against population growth, demand increases and climate extremes.
For more insights into our industry, and solutions to some of the key challenges, visit AECOM’s 2018 Future of Infrastructure report here’