Seasons – June 2022

Water gives life to the natural world. Without water, soils become dirt, plants perish, and animals vanish. Other than water stored in lakes and rivers, rainfall is the only source of life-giving water.

In Texas, the amount of water that falls on a particular piece of property varies greatly depending upon its geographic location. The Piney Woods of East Texas can receive 50-60 inches of rain in a year while the deserts of West Texas can barely count on 8-10 inches of annual rainfall. Annual rainfall in the rest of Texas falls between these two extremes. The amount of water that is available through rainfall on any given piece of property can be referred to as the “water budget” of that property. In order for landowners to establish what the water budget is on their property, they need to first understand where their property lies geographically in Texas. The map below, created by the Texas Water Development Board, illustrates the average yearly rainfall by county in Texas.

Once the amount of rainfall (the “income” in the water budget) is determined, then a landowner can begin to plan for the best way to manage that budget.

Considerations for Water Retention

Like all budgets, the income must be balanced against expenses. Savings accounts should be developed to protect against variances in income and increases in expenses. In order to devise an effective water budget, it is important to understand the things that affect the amount of water that can be retained from the original rainfall input. These “expenses” are:

• Evaporation – the return of water to the atmosphere from the surface of leaves, bare ground, water bodies, and impervious surfaces (roofs, roads, etc.).
• Transpiration – the exhausting of moisture from plants and animals.
• Interception – plant cover that does not allow for rainfall to reach the ground and is a source of both evaporation and transpiration.
• Runoff – the flow of water across the surface of the land.

Water retention can be considered the “savings account” in the water budget. Water can be retained in ponds and lakes, wetlands and marshes, moist soils, and, ultimately, by infiltration that may eventually recharge aquifers for underground storage.

Things to consider when managing land to maximize the retention of water are:

• Local climate – humidity levels affect evaporation rates.
• Aspect – the relationship of a property to the sun, i.e., west, and south-facing slopes have a higher evaporation rate and are drier than east, and north-facing slopes.
• Slope angle – steep slopes can allow for more runoff and less infiltration.
• Impervious cover – exposed rock, hardened soils, roads, and rooftops.
• Plant Cover – density and types of plants that are located on the property.

The illustration above shows how the “Water Cycle” works. Inputs from rain are balanced against evaporation, transpiration, runoff, infiltration, and recharge.

Now that the planning parameters have been established, it’s time to come up with a water budget for a sample piece of property:

Let us say that a landowner has a 60-acre piece of property located in Blanco County. The terrain is rolling hills with an intermittent creek flowing through the middle of it. Along the creek are flat, deep-soiled “benches”. Most of the hills are south facing and the hilltops have very shallow, rocky soil. According to the map above, the average rainfall for the area is 30-35 inches per year. The climate is moderately humid.

In order to maximize water retention on the property, the best approach would be to increase infiltration by slowing the flow of water across the deep soil areas along the creek and on the hilltops and decreasing runoff from the hills intercepting rainfall on the steeper slopes. The runoff of water in the intermittent creek could be decreased during high volume rain events by the establishment of trees and woody shrubs within and along the banks of the creek.

Photo and graphic provided by the Natural Resources Conservation Service. On the left shows a riparian corridor with trees along the banks to slow the surface flow of water. On the right shows how nutrients are trapped in the ground when you slow surface flow.

With these management parameters in mind, how would the landowner actively manage the property to achieve these goals?

• Reducing grazing pressure on the hilltops and creek sides would allow for tall grasses to grow, slowing the flow of water across the land, thereby improving infiltration.
• Planting a diverse blend of native grasses and perennial forbs (wildflowers) could help speed up infiltration.
• Allowing trees and shrubby plants to grow on the steep slopes would increase interception of heavy rainfall and allow it to slowly move through the leafy vegetation and be absorbed in the ground beneath the woodlands. Some water, captured by the bark and leaves of the trees would be infiltrated into the soils through stem flow within the trunks of the trees. Evaporation rates would be reduced by the increased shade provided by the woodlands on the slopes and the tall grasses covering the shallow soils on the hilltops.
• The planting and natural recruitment of trees and woody plants along and within the banks of the creek would both provide shade to reduce evaporation of any standing water in the creek and, with the presence of roots and trunks, slow water flow during heavy rains and facilitate the development of gravel beds that would act as small dams, creating more permanent pools of water within the creek bed.

Once these practices are established, periodic management of the grasslands by short-term grazing, mowing, and/or the application of prescribed fire will be needed to maintain them. The wooded areas will be self-tending.

These management practices not only help increase the infiltration and retention of water, but they also provide habitat for wildlife and are aesthetically pleasing. It takes patience for landowners to manage their land to slowly become a natural sponge. Planting native grasses can be expensive and natural recruitment of woody plants takes time. However, the benefits to the water budget, wildlife, and the pride of ownership make these management practices very much worthwhile.

Have questions about improving the water retention on your land? Please contact us at [email protected] or (512) 894-3479.