Water Diversion Terraces

While looking at the freshly disturbed waterline right-of-way from Hamilton Pool Road one will notice that the waterline traverses slopes on all portions of the right-of-way that are visible from the road. No earthen water diversion terraces can be seen from the road. Loose soil along the slopes is protected only by temporary silt fences.

What is likely to happen is that during hard, washing thunderstorms, loose soil will wash downhill and accumulate against the silt fences. When soil washes downhill the structure and the texture of soil is irreparably damaged, so that soil damage occurs even though the LCRA may be able to blade some of the soil back into place. Silt fences are for construction phase erosion control only. Grass plants, yet to grow, would provide some protection from erosion; but warm season perrenial grasses normally require three to five years to mature. Vegetative cover is subject to damage by drought, by vehicular traffic, and by disease and should therefore be augmented by permanent terraces. Even with the right-of-way fully revegetated, permanent terraces will be needed to divert water from the right-of-way into more gently slopeing areas, thereby reducing erosion caused by water rushing down the right-of-way.

The U. S. Department of Agriculture, N. R. C. S. has provided some guidance addressing erosion along pipeline rights-of-way in a publication titled "Guideline for Re-establishment of Vegetative Cover on Disturbed Areas Along Pipilines" in which the U. S. D. A. recommends that diversion terraces be constructed across pipeline rights-of-way at intervals of about 50 to 150 feet depending on steepness of slope and safe outlets to prevent run-off water from following the pipeline. The U. S. D. A. guideline provides a rule of thumb formula for determining the hieght and spacing of terraces. Most such terraces are less than two feet high and do not create a visual problem or an obstacle to vehicular traffic. One helpful function terraces perform is to reduce erosion caused by water runing down trails made by livestock and by pipeline service vehicles used to operate and maintain the pipeline.

Correctly located and constructed permanent terraces reduce erosion by creating proper water diversion. Proper water diversion along the right-of-way is important to the health of the watershed. The LCRA should protect our watershed by providing water diversion terraces that are appropriate to the terrain and consistent with individual preferences of landowners along the right-of-way.

Henry