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Darcy's Law to Estimate

A waste disposal facility is to be constructed in the area shown over the page (please see attachment). Two piezometers have been constructed with water depths as shown. The facility will be 278m long parallel to the local flow direction, and 200m wide. The waste will be stored in trenches 13m deep into the oxidized till, which has a water table 5m below the land surface, and a hydraulic conductivity of 10^-7m/s. The underlying unoxidized till has a hydraulic conductivity of 10^-8m/s. Measurements have shown a hydraulic gradient of about 0.082 across the site. A trench 13m deep will be dug parallel to the width of the site, which will act as a drainage trench. Both till layers have an approximate porosity of 15%. Use darcy's law to estimate:

(a) What is the horizontal pore fluid velocity in the oxidized till layer?

(b) What is the volumetric flow rate into the drainage trench?

(c) What is the vertical hydraulic gradient between the aquifer and the oxidized till?

(d) What is the vertical pore fluid velocity through the unoxidized till layer?


Solution Preview

(a) The average fluid velocity within the pores, called the seepage velocity V, is the Darcy velocity divided by the effective porosity of the medium. It can also be expressed as:
V=q/n where q= -K (i)
V = seepage velocity, q = darcy's flow, n= porosity, -K = hydraulic conductivity, i = change in hydraulic head over length/hydraulic ...

Solution Summary

The expert examines Darcy's Law to estimate. The horizontal pore fluid velocity in the oxidized till layer is determined.