Groundwater - Layers and soil properties

9 important questions on Groundwater - Layers and soil properties

What are the hydrogeologic layer types?

-phreatic aquifer/upper aquifer: groundwater table is located in this layer, top of layer is unsaturated. Because groundwater levels change, the conductance of this layer changes as well
-confined aquifer: always completely saturated
-semi-confined aquifer: the aquitard on top does not completely cover the aquifer
-aquitard/confining uit/poorly permeable layer
-aquiclude: resistance is so high that no water flows through it   
-hydrological base: In NL: impermeable geological deposition, about 300m below soil surface. Deeper waters can be both saline and warm (possibly above 100 degrees C)

What are the 2 distinctions made in sediment?

-consolidated sediment: bedrock
-unconsolidated sediment: sand, clay and gravel

What is effective conductivity?

The weighted average of the conductivities of separate layers. (keff in m per dag)

Effective conductivity of layer 1,2,3 is
(k1xD1+k2xD2+k3xD3)/(D1+D2+D3)
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Why does organic soil have a low conductivity?

Because it consists of decomposed plants which have much water fixed in stems in leaves.

What determines the saturated conductivity in peat soils?

The aeration.

How is the conductivity of flow of certain directions described?

-anisotropic: conductivity is higher in one direction than the other, common in consolidated sediments, where fractures in the bedrock have a large impact on the flow direction
-isotropic: conductivity is the same in all directions

What is the saturated hydraulic conductivity?

The maximum conductivity reached when the soil is saturated. In groundwater conductivity is always the saturated hydraulic conductivity

What is the difference between phreatic aquifers and confined aquifers?

Phreatic aquifers include the groundwater table and confined aquifers are enclosed by an aquitard on top.

What is the hydrological base?

A certain lower boundary beneath which water does not take part in the hydrological cycle any more.

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