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What is a watershed?

Everyone in the world lives in a watershed. A watershed is an area of land that collects the water within a specific area and drains into the same location or body of water. Our well being, economy, and quality of life all depend on healthy watersheds.

 

The Cypress Creek Watershed

Cypress Creek is a major tributary of the Blanco River located in the central Texas Hill County in southern Hays County. The Cypress Creek watershed rises from Jacob’s Well and flows through the city of Woodcreek and into the Blanco River at Wimberley. The Cypress Creek and the Blanco River combine at the confluence in the south side of Wimberley, just upstream from the Blanco River/RR12 junction.

 
 

It’s rugged terrain, narrow canyons, and cool, clear springs define the landscape. The watershed is home to a unique set of rural and urban communities, habitats, and ecosystems that rely on groundwater from the Trinity Aquifer. Used primarily for residential and commercial water supplies in the area, this groundwater supports the thriving economy of the valley. As a significant source of surface water base flows, it also provides valuable riparian habitat to a wide diversity of species, including fishes, waterfowl, reptiles and amphibians, mammals, and insects. A healthy, diverse riparian system in turn helps maintain water quality and quantity.

Based on historic streamflows, Cypress Creek has dry and flowing segments. Unless heavy rainfall occurs, the 9.5-mile segment above Jacob’s Well is usually dry (Figure 1.1). Jacob’s Well, an artesian spring, contributes perennial flow for the 5.5-mile long downstream segment, known as Cypress Creek. The lower part of the creek’s stream gradient is 21.4 ft./mi.

 

Climate

The Cypress Creek Watershed lies within the approximate boundary between the subtropical humid climate to the East and the subtropical subhumid climate to the West. Data from 1971-2000, suggests that the average annual temperature in Hays County was 76 to 78 °F (24.4 - 25.6 °C), average annual rainfall was around 35 inches (889 mm), and during the years 1950-1979, annual gross lake surface evaporation averaged around 60-65 inches (1,524 – 1,651 mm). The region also experiences extremes in weather patterns, observed over the decades as flash floods and droughts.

Climate in the area follows the general pattern of the Texas Hill Country; peak rainfall tends to occur in the summer and fall, and temperature in the area is highest from May through October, resulting in predictable summer weather patterns. The period of July through September is often both hot and dry, with average daily temperatures above 80°F and little rainfall.  Since water quality in the Cypress Creek is highly dependent upon flow, summer months are likely to have water quality impairments including low dissolved oxygen, high algal density, and increased water temperature.


Water flow in the Cypress Creek Watershed

The Cypress Creek watershed exemplifies the highly interactive groundwater and surface water systems characteristic of the Hill Country region. The creek flows through unincorporated portions of Hays County and the cities of Woodcreek and Wimberley where it meets the Blanco River near the town center. Jacob’s Well, an artesian spring about five and a half miles upstream of the confluence, is considered the lifeblood of the community as it perennially feeds water to the lower third of the creek. The spring is an expression of underground water stored in the Trinity Aquifer that surfaces in the bed of the creek. In the upper reaches of the watershed above Jacob’s Well, Cypress Creek remains dry most of the year. During rain events, however, water flows downhill from the distant hilltops in the watershed and into the creek. Once the water is in the creek bed, part of it flows back underground into the aquifer through karst recharge features. Recognition of the complex interconnections between groundwater and surface water is critical to protecting water quantity and quality in the watershed.

Why it's important

Hays County is projected to grow by approximately 300% in the coming years. This is an important consideration for all future natural resources management, particularly water. Such rapid growth exerts pressure on all natural resources, particularly water. Increased demand for drinking water in an area that already relies heavily on groundwater will likely result in significant aquifer drawdown. Lower aquifer levels translate into lower baseflow in springs and creeks; low or intermittent flows negatively impact riparian vegetation, wildlife habitat, and ultimately water quality. More residential and commercial development also means more impervious cover in the form of roads, driveways, and parking lots. Impervious cover causes greater volumes stormwater runoff directly into rivers and creeks. Without the benefit of filtration through plants and soils, increased runoff poses a serious threat to water quality. The Watershed Protection Plan is designed to mitigate these impacts through stormwater management practices that use green infrastructure to slow, capture, and filter water before entering surface water bodies and aquifers.