South Grape Creek flows into the Pedernales River just north of US Hwy 290E near the junction of Pfieffer Road and Wahrmund Rd.
Normally, South Grape Creek is a gentle flowing creek where children can safely play. When rainfall as little as 1-2″ combines with drainage from surrounding agricultural enterprises, the runoff can quickly increase the rate of flow of the creek to dangerous levels.
This video shows the runoff from surrounding agricultural lands flowing into the river after a 2.69″ rain event over 48 hours. (See CoCoRaHS)
The runoff has cut through the soil creating steep banks or cut banks, on its way to the creek. The runoff pours over the edge of the upper bank, further eroding the land.
Sediment is considered a pollutant. When water runs clear it has little to no sediment in it. When the water is muddy, it is clogged with sediment.
Usually, in riparian areas, you will find grasses, small bushes and trees trapping the sediment. Unfortunately, this gully has little to hold the soil in place.
Note the color of the runoff in this video. The runoff is a light brown indicating the water is carrying sediment downstream into the creek.
This area is at the north end of South Grape Creek, not far from its confluence with the Pedernales. The soil in this area is a fine sand and clay. This type of soil does not absorb water quickly and when thoroughly wet, not at all. Runoff happens.
See the Web Soil Survey website for more detailed information on soil types.
South Grape Creek is a much loved spring-fed creek in this area, where children play along the creek banks and wade in the water. If large developments are permitted to dump treated waste water, a euphemism for sewage, into the creek there eventually will be no creek to play in. The creek will clog with algae buildup and eventually slow the creek to a sewage-laden rivulet that will surge with thoroughly polluted water each time it rains. The polluted sludge will kill the fish and frogs, poison the animals that come to drink and the sludge-laden flow, with its sediments and sewage, will pour straight into the Pedernales River.
