Layering and Its Control on Groundwater Flow

Many rock types have a layered structure, individual rock layers varying in thickness from a few centimeters to tens of meters. Layered rocks include marine sediments, most continental sediments, lava flows and volcanic ejecta, and intrusive sills. The hydraulic properties vary from one rock layer to another, often resulting in abrupt changes along the vertical axis. In terms of the permeability coefficient (k) the lateral coefficient (kx) may significantly differ from the vertical coefficient (kz). The alternation of aquifers and aquicludes results from the layered structure of different rocks, and the occurrence of springs is often controlled by the layering of rocks. Fissures may be restricted to individual rock layers or cross several rock beds, in which case water flow is improved, mainly in the vertical direction. 

4 Folded Structures and Their Bearing on Flow Direction, Confinement, and Entrapment 

Marcel Dekker, Inc. 270 Madison Avenue, New York, New York 10016 

Confined aquifers (section 2.8) are rare in tectonically undisturbed regions with horizontal rock beds (Fig. 3.5). Tilting of the aquifer and aquiclude sandwich makes room for the formation of confined aquifers. It provides each case with a recharge outcrop section, forming a phreatic aquifer (section 2.8) and a confined section fed by the former (Fig. 3.6). 

Subsidence structures are common. They are formed by the gradual lowering of rock strata, forming basin shapes. Two major processes operate during subsidence burial of older rock beds and accumulation of new sediments at the surface forming new rock beds or lenses that eventually get buried as well, the water stored in them becoming trapped (Fig. 3.7). 

---