Texas has a diverse array of rivers, aquifers and other ecosystems-these features maintain Texas' unique natural history while supplying water to meet the needs of people. However, the state's water supply is finite, and already stressed by an expanding population and natural drought cycles.
What does the Texas Water Explorer tell us about Water Quantity?
Modeled River Flow Alteration
When river flows are regularly depleted, both ecological integrity and water security for human populations are diminished. We used the TCEQ Water Availability Models to estimate the level of flow alteration in Texas' rivers and summarize alteration patterns across the state.
Flow Depletion - 14% of the state's rivers and streams have flows regularly depleted by more than 50% from the natural conditions.
Alteration of Natural Flow - Flow in 41% of the state's rivers and streams are regularly outside of a presumptive e-flow standard (+/- 20% of natural flows); 31% are frequently under the standard, 2% are frequently over the standard, and 9% are regularly both above and below the standard.
Water Use by Sector: Past, Current, Future
Texas freshwater supplies a growing population and helps maintain a varied economy. This indicator examines patterns in water use by sector across Texas and summarizes the information for river basins, aquifers and counties.
Water Use by Sector - Irrigation (59%) and municipal (28%) water use account for most of the total water use in Texas. Irrigation accounts for 80% of groundwater use and municipal water use is the largest surface water use sector, accounting for 45%.
Overall, use of water for municipal purposes is increasing and use for irrigation is decreasing; this pattern is most prominent in groundwater.
Municipal is the largest water use sector for eight Texas river basins, while irrigation is the largest use sector for six basins. Manufacturing is also the largest water use sector for six basins, while steam-electric power is the largest for two basins and livestock the largest for one.
This indicator examines reservoir storage across Texas river basins and the ability of the reservoir system to buffer against drought.
Reservoir Storage - Of the state's 23 river basins, five (Canadian, Trinity, Colorado, Nueces, and Rio Grande) have sufficient reservoir storage capacity for at least a full year's worth of total average annual flow in the basin.
Trends in 7-Day Minimum Flows
Many Texas rivers are experiencing longer periods of low flow due to increased water withdrawals and severe drought. This indicator examines patterns across Texas by analyzing changes in the 7-day minimum flow (the lowest flow during a year that lasts seven days).
7-Day Minimum Flows - Of 171 Texas streamflow gauges analyzed, 121 have seen declines in 7-day minimum flow over the last 20 years, and 51 of these are statistically significant declines.
Trends in Magnitude of Small Floods
Periodic high flow events are part of the natural flow patterns of Texas rivers, and are important to maintaining healthy freshwater ecosystems. This indicator examines how small flood magnitudes (the average peak flow magnitude of any small flood events during a year) have changed in Texas rivers over the last 20 years due to factors such as dam operations.
Small Floods - Of 256 Texas streamflow gauges analyzed, 80 have seen changes in small flood magnitude over the last 20 years, with 42 declining and 38 increasing.
Trends in Aquifer Level
Texas' aquifers are becoming increasingly stressed by a growing population, drought and changes in aquifer recharge patterns. We examined the pattern of changes in aquifer levels across Texas, which is an important indicator of aquifer health.
Aquifer Levels - Of 4,420 groundwater monitoring wells analyzed, about 50% (2,333) have experienced declining water levels over the full available measurement period. The highest incidences of water level declines are in the Hueco-Mesilla Bolson, Ogallala and Carrizo-Wilcox aquifers.
42% of wells have seen declines since the year 2000, with the highest incidence of declines in the Hueco-Mesilla Bolson, Seymour and Carrizo-Wilcox aquifers.
Some areas of the state (such as portions of the Gulf Coast, Pecos Valley, Edwards-Trinity and Trinity aquifers) have seen levels stabilize recently after periods of decline.
Trends in Groundwater Contribution to Baseflow
In Texas, groundwater and surface water are intimately connected and function as one unified resource. This indicator examines how the baseflow of groundwater-fed rivers has changed over time due to factors such as groundwater pumping and drought.
Trends in Baseflow - Of 118 Texas streamflow gauges analyzed, 14 (12%) have seen long-term declines in groundwater-fed baseflow over the full available period of record; 27 (23%) have seen declines over the last 20 years.
Groundwater Use Relative to Management Restrictions
To maintain Texas' aquifers, groundwater pumping for human uses must be balanced with the health of the surface and subterranean aquatic ecosystems that aquifers support. This indicator examines the compatibility of current levels of groundwater pumping with the pumping limits set by a state planning process designed to balance all these needs.
Groundwater Management Restrictions - 81 counties in Texas already have total annual groundwater pumping in at least one aquifer that exceeds management targets (2010 Modeled Available Groundwater) set to maintain desired future conditions for Texas aquifers.