Beginning near the Texas-New Mexico border and flowing through to the Gulf of Mexico, the Colorado River is the largest river entirely contained within the state of Texas. The lower portion of the river issues from the Balcones Escarpment at Austin, an inactive fault zone that forms the boundary between the rugged Hill Country and the rolling Coastal Plain (Floodplain coalition, Historical Association).

The Colorado River basin is prone to drought punctuated by extreme flooding. Efforts to “harness” the river necessitated the creation of the Lower Colorado River Authority, a non-profit public agency that delivers flood control, electricity, and the water supply to over a million people (Hist Asso). The LCRA manages 600 miles of the Colorado, from San Saba to the Gulf Coast, through a series of reservoirs known as the Highland Lakes. By regulating flow through six massive dams, the LCRA balances the water supply needs of municipalities, industry, agriculture, and environmental flows through a state approved Water Management Plan, last updated in 2015. Although the Highland Lakes are located northwest of Austin, their influence defines the Colorado River all the way to the Gulf of Mexico (LCRA).

The river has supported agricultural irrigation for more than a century, including a $300 million rice industry on the coastal plain (Hist Comm). The LCRA manages a 1,100-mile network of irrigation canals in Colorado, Matagorda, and Wharton counties. When river flows are not sufficient, the LCRA can release water from lakes Travis and Buchanan; however, severe drought interrupted these flows from 2012-2015 (LCRA). While balancing human needs, the LCRA must meet environmental flow requirements as recommended by the TCEQ to maintain the ecological environment of the river basin, estuary, and bay system (TCEQ, LCRA). When there is enough water upstream, these daily releases are pulsed for the generation of hydroelectric power during peak demand, causing river level fluctuations (LCRA).

The LCRA holds the right through state issued surface water permits to up to 1.5 million acre-feet per year from lakes Buchanan and Travis and 636,750 acre-feet per year “under downstream run-of-river rights” from irrigation operations (LCRA). Excess runoff due to rainfall in the basin below the Highland Lake Reservoirs is considered lost (Kevin Anderson doc). The LCRA is in the process of increasing the water supply by 90,000 acre-feet per year with the construction of the Lane City Reservoir in Wharton County. The new reservoir will allow for downstream capture and storage, and is expected to be operational in 2018 (LCRA).

Below the Highland Lakes lies Lady Bird Lake, formed by Longhorn Dam and operated by Austin Energy. The dam has outlived its original function in forming a reservoir used to cool a power plant, and the City of Austin is currently contemplating its future (Statesman News). From here, the Colorado is freed from its narrow channel at the last dam it encounters for now, but the hydrologic alteration due to extraction and releases via the LCRA and Highland Lake Reservoirs are the primary threat facing the river.

Below Longhorn Dam, the river widens and slows as it flows southeastwardly across alluvial bottomlands of the Coastal Plains with its sand bars, shoals, deltas, creek mouths, and remnants of floodplain forest (Anderson). The river enters the Gulf of Mexico at Matagorda Bay, the second largest estuary on the Gulf Coast at over 352 square miles. This important ecological resource supports the production of commercial and sport fisheries. Freshwater inflows, influenced by dams over 200 miles away, are vital to the health of this ecosystem (TPWD).

Sources:

1. TX CO River Floodplain Coalition: http://www.tcrfc.org/wp-content/media/00FrontMatter.pdf
2. Texas State Historical Association: https://www.tshaonline.org/handbook/online/articles/rnc10
3. LCRA
4. TCEQ
5. Statesman news: http://www.mystatesman.com/news/news/local/austin-officials-exploring-an-overhaul-of-longhorn/nmwJX/
6. Kevin Anderson doc: https://www.nps.gov/ncrc/portals/rivers/projpg/colorado.pdf
7. TPWD: http://tpwd.texas.gov/landwater/water/conservation/freshwater_inflow/matagorda/