WELL HYDRAULICS

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# WELL HYDRAULICS - PowerPoint PPT Presentation

WELL HYDRAULICS. Well Hydraulics. What is well hydraulics? To understand the processes affecting when wells are pumping water from an aquifer Why is it important?

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Well Hydraulics

What is well hydraulics?

To understand the processes affecting when wells are pumping water from an aquifer

Why is it important?

Ground water withdrawal from aquifers are important to meet the water demand. Therefore, we need to understand well hydraulics to design a pumping scheme.

The easiest way to understand well hydraulics is to study a Single-well behavior in an aquifer under steady flow conditions.

Transient Flow to a Single Well

Confined aquifer

Assumptions

• Well is pumped at a uniform rate
• Well is fully penetrating across the aquifer thickness
• Aquifer is homogeneous and isotropic
• Well/screen losses are ignored
Transient flow in a confined aquifer with one pump

Question

What is the drawdown, s at distance r and time t for pumping rate Q?

s=h0-h

Theis Solution

Solution to the transient confined aquifer flow

equation is

where

Note: u is dimensionless

Theis Solution

Use the Well function [W(u)]table and find drawdown s as

Theis solution can be used to estimate drawdown in an unconfined aquifer as long as the drawdown s is not large; i.e., compared to the initial thickness of the aquifer.

Example

A well is pumping from a confined aquifer at a rate of 10,000 m3/day. The transmissivity and S of the aquifer are 1000.7 m2/day and 0.0001, respectively.

Find the drawdown with time at two locations 100 and 200 m from the well.

Example

Procedure

• Pick a series of times for each observation location.
• Knowing the radius, r, time, t, T, S, and Q, find u for each time value.
• Using the well function, find W(u) for each u
• Use the solution to find s at that r and t.