Author Question: What conditions contribute to saltwater intrusion? What will be an ideal ... (Read 47 times)

debasdf · **on:** Jul 15, 2018

What conditions contribute to saltwater intrusion? What will be an ideal response?

Question 2

How did use of groundwater affect surface water resources in the case of the San Joaquin River,
California? What will be an ideal response?

jlaineee · **Reply #1 on:** Jul 15, 2018

Answer to Question 1

Seawater and freshwater occur as separate bodies in the subsurface because of density differences.
Freshwater floats on top of denser saltwater. This occurs even in open water bodies until currents or
waves mix the two. Underground, these water bodies are isolated from forces that would tend to mix
them and are layered or stratified as a result. The position of the boundary between these water masses
is a function of water pressure. In coastal areas, increased outflow of freshwater will push the
boundary seaward, and decreased outflow will bring about saltwater invasion. Decreased flow of the
Nile River, after completion of the Aswan High Dam, has deprived the Nile Delta of water, thereby
causing saltwater to invade the area. Saltwater invasion can also occur locally as the result of pumping
in coastal areas. Not only is the water table drawn down, but the boundary between the fresh and
saltwater bodies is also drawn upward.

Answer to Question 2

Heavy groundwater withdrawals lowered the water table to the extent that the river changed from a
gaining stream in 1906 to a losing stream by 1966. This had a profound impact on surface water flow
because of losses to the subsurface.