Winterbournes generally form in areas where there is chalk ( or other porous rock ) downland bordering clay valleys or vales.
22.
By some estimates, it may contain 18 trillion feet of natural gas in porous rock formations deep beneath the ocean floor.
23.
Deformation bands are present in a variety of porous rock types such as sandstones, limestones, siltstones, poorly welded volcanic tuffs, and breccias.
24.
The Freudenstein Tunnel is through the porous rock strata, which flows as a result of heavy rains on the hillsides above it.
25.
The porous rock must be capped by a layer of low permeability which acts as a seal, or caprock, for the CO 2.
26.
There are numerous sinkholes, where surface water disappears through the porous rock surface, and extensive cave systems have been formed in some areas.
27.
Over time, the water seeps through porous rocks under the butte and now emerges on the north side of Black Butte at Metolius Springs.
28.
Also, pumping so much water into porous rock confined between impermeable layers could, in theory, crack the ceiling or floor, some geologists have said.
29.
The method is based on the existence of the boulder zone, a layer of porous rock at the lower depths of the Floridan Aquifer.
30.
In times of surplus, water would be pumped into this layer of porous rock, then pumped out when supplies are low, city officials said.
