Lab 10 - Soil Water Movement Flow Model Experiment 1 –Red dye is added to the waste lagoon and to a well in the unconfined aquifer. –Green dye is added to a well in the confined aquifer. –Without pumping and without streamflow, the aquifer is in a hydrostatic condition. Flow Model Experiment 2 –Red dye is added to the waste lagoon, underground storage tank, and all surficial aquifer wells. –Green dye is added to the two left confined aquifer wells. –An extension is added to the artesian wel l (we will learn what an artesian well is soon)

Darcy’s Law, Q = A K G –A = The area of flow The greater the area, the greater the flow. –K = The hydraulic conductivity or permeability The higher the conductivity, the greater the flow. –G =  H / L = The magnitude of the driving force The steeper the water slope, the greater the flow

Soil Water Movement Total Head: –h = z + p = z -  Hydraulic Gradient, G –  in energy w/ distance –G =  h /  x Hydraulic conductivity, K –a function of pores sizes and pore connectivity –K = C d 2

Typical Values –Gravel, lava, caves K = 10 cm/s –Sands K = 20 cm/hr –Soils K = 5 cm/day –Clays K = 0.9 cm/yr Hydraulic Conductivity

Unsaturated Hydraulic Conductivity Less than the Saturated Conductivity!! –q = K u G = K K r G –K u = K K r = unsaturated hydraulic conductivity –K r = relative hydraulic conductivity

Subsurface Potentials

Problem 1. Do in lab with your instructor Given: Most soils have a particle density of 2.65 g/cm 3. The porosity of a specific soil is A sample of this soil weighs 122 g at field capacity The soil sample weighs 103 g at the wilting point. The soil sample weighs 100 g after being oven-dried. The soil sample is part of a soil horizon that is 20 cm thick.

Questions: 1.What is the bulk density of this soil? 2.What is the gravimetric water content at field capacity? 3.What is the gravimetric water content at the wilting point? 4.What is the volumetric water content at field capacity? 5.What is the volumetric water content at the wilting point? 6.What is the maximum depth (in cm) of water available for plants for this soil?

Problem 3. Do in lab with your instructor Given: Irrigation has been applied to a row crop field, as shown in the figure. The field is one hectare (100 m x 100 m) in size. The soil water conditions are uniform over the field. The water tension at A is 1 m (pA = -1 m). The water tension at B is 3 m (pB = -3 m). The water tension at C is 5 m (pC = -5 m). Remember, one bar = 10 m, 0.1 bar (field capacity) = 1 m.

Questions: 1.What is the hydraulic head (h = z + p) at A and C? 2.What is the direction of flow between A and C? 3.What is the hydraulic gradient (i = ∆h/L) between A and C? 4.What is the specific flux (q = K ? i) between A and C? 5.What is the total flow (Q = qA) in L/s?