Dr. Martin T. Auer Michigan Tech Department of Civil & Environmental Engineering Water Supply

The Hydrologic Cycle (overview) Units = m 3 per year = 12 x the volume of Lake Superior per year

The Hydrologic Cycle (detail)

Drinking Water Sources Approximately two-thirds of the population of the U.S. receives its supply from surface waters. However, the number of communities supplied by groundwater is four times that supplied by surface water. This is because large cities are typically supplied by surface waters and smaller communities use groundwater.

Kankakee River Basin

The Hydrograph Discharge Time Direct Runoff Hydrograph Base Flow

Unconfined Aquifer water table

unconfined aquifer water table unconfined aquifer re-charge water table well Unconfined Aquifer confined aquifer re-charge confined aquifer confining layer piezometric surface = f (K) Confined Aquifer

water table Unconfined Aquifer Confined Aquifer piezometric surface aquiclude Piezometric surface (manometer)

unconfined aquifer water table unconfined aquifer re-charge water table well Unconfined Aquifer confined aquifer re-charge confined aquifer confining layer piezometric surface = f (K) Confined Aquifer

Groundwater Supply

Flow through a cylinder

Cone of Depression

Effect of Pumping Rate on Cone of Depression

Effect of Multiple Wells

Small soil particles pack together more closely than large particles, leaving many small pores. Large soil particles pack together less closely, leaving fewer, but larger, pores. Most soils are a mixture of particle sizes. Poorly sorted soils (greater range of particle sizes) will have a lower porosity, because the smaller particles fill in the "gaps“. Porosity and Packing A given volume of spherical solids will have the same porosity, regardless of the size of the particles. The significance of porosity lies in role of surface tension (higher for small pores) in retaining water and frictional losses in transmitting water.

Clays are small soil particles and thus one expect tight packing. However, the net negative charge of clay particles separates them, resulting in a higher porosity than for a sphere of equivalent volume. Sands are large particles, more regular in shape than silts and thus having a porosity similar to that expected for spherical particles. Porosity of Specific Soils Silts are intermediate in size between clays and sands and are irregular in shape. This irregularity leads to poor packing than for spherical particles of similar volume and thus a higher than expected porosity.

Porosity Values MaterialPorosity (%)Comment Clay55negative charge Loam35irregular shape Coarse sand30regular shape soil particles pores The net effect of the physicochemical properties of clay, silt and sand particles is that the porosity and thus water content tends to decrease as particle size increases.

Specific Yield This is the amount of water, expressed as a %, that will freely drain from an aquifer

Specific Yield Having a lot of water does not mean that an aquifer will yield water. Surface tension effects, most significant in soils with small pores, tend to retain water reducing the specific yield. MaterialPorosity (%)Sp. Yield (%) Clay553 Loam355 Coarse sand3025 A better expression of the water available for development in an aquifer is the ratio specific yield to porosity. MaterialRatio of Specific Yield : Porosity Clay0.05 Loam0.14 Sand/Gravel0.83

Hydraulic Gradient

Hydraulic Conductivity and Transmissibility

H M2M2 M1M1 E S1S1 S2S2 h1h1 h2h2 h = H - s r1r1 r2r2 An extraction well (E) is pumped at a constant rate (Q) and the drawdown (S) is observed in two monitoring wells (M) located at a distance (r) from the extraction well. Determination of Hydraulic Conductivity Hydraulic conductivity (m 3 ∙m -2 ∙d -1 ) is then calculated using the equation below:

At maximum drawdown, conditions at r 1 (the well radius) are s 1 = H and h 1 = 0 and conditions at r 2 (the edge of the cone of depression) are s 2 = 0 and h 2 = H. Estimating Well Production H E S1S1 S2S2 h1h1 h2h2 h = H - s r1r1 r2r2 And the maximum pumping rate (m 3 ∙d -1 ) is calculated using the equation below: