The land tract is approximately 200 acres of typical Texas Hill Country, a rolling topography with rock, brush and scattered oak trees. The project goal was to divert rain water runoff that was sheeting across the ground and threatening the house located down slope.
I see these types of problems all across the country. In most cases the problem is the result of poor, uninformed planning on the part of the landowner or urban development in a close proximity to the effected site which catastrophically effects drainage on surrounding properties. In this case the house was located in a flat water runoff area and was constructed with poor elevation and drainage techniques. A large and extensively long berm was required to divert the water around the house. Diverting water from a large area into a smaller area quite often channels the water into a narrower stream making the water run deeper and with more velocity and energy. Extreme soil erosion and deep washouts in the landscape can be an unwelcome result of re-directing the water without careful consideration of the results.
The water related challenges were four fold-
- Where to generate the dirt necessary to build the water diversion berm.
- How to integrate the berm positively into the surrounding aesthetics.
- How to slow the diverted water down so that erosion issues were not created.
- Since water is a precious resource and getting more valuable by the day, what can we do to make use of the diverted water?
The answer was to create a long and relatively narrow lake that would capture the water runoff reservoiring the water for recreational purposes. The excess water in the lake would then be released slowly by sheeting the water over a wide area in a shallow fashion. The lake discharge point would release the water in an area so that it would no longer threaten the house.
What size to make the lake centered on five requirements-
- Generating enough dirt for the dam.
- Generating enough dirt for the privacy berm along the county road.
- Generating enough clean dirt to cover the plastic liner once installed.
- Generating enough top soil to cover all of the areas to be seeded.
- Blending all of the aesthetics into the overall landscape and infrastructure.
Most of these requirements would be beyond the scope and capabilities of a local dirt contractor. Most of them have no idea of how to install a plastic lake liner. Most of them are not capable of aesthetically blending the lake construction project into the existing topography and infrastructure.
As with many Hill Country projects the soils were not conducive to holding water so a plastic lake liner was used. Plastic liners are great and will last a very, very long time if the proper materials are used and the plastic liner is installed properly. There are many types of plastic liners and ways to install them but only a few liners and installation practices are considered truly permanent. Improper liner materials and/or poor installation of the liner will result in a plastic liner failure.
On this lake building project the sub grade compacted smoothly and the liner cover dirt was clean so a 60 mil HDPE plastic lake liner was used. A geo composite liner cover was used to protect the liner where rip-rap rock fore erosion control was used on the inbound waterways.
An 8 inch PVC siphon pipe was used to establish the water elevation. The siphon pipe will discharge “dead” water (stagnant and low on oxygen) from the lower lake depths once the water elevation reaches a full level. Discharging the dead water lying in the lower depths is preferable to discharging the water on the lake’s surface because the surface water is fresh and full of oxygen. Quite often after a long hot summer when the fall rains come and your lake discharges for the first time the water will smell like a sewer