Theis confined-well drawdown model
For constant pumping from an ideal confined aquifer, drawdown at radius r and time t is s=QW(u)/(4πT), where u=r²S/(4Tt) and W(u)=∫ᵤ∞e^(−ξ)dξ/ξ.
Key knowledge
For constant pumping from an ideal confined aquifer, drawdown at radius r and time t is s=QW(u)/(4πT), where u=r²S/(4Tt) and W(u)=∫ᵤ∞e^(−ξ)dξ/ξ. The response depends jointly on transmissivity T and storativity S. Fitting an observed curve estimates model parameters only if the aquifer and observation process satisfy the assumed model.
Values and equations
s=QW(u)/(4πT); u=r²S/(4Tt); W(u)=∫ᵤ∞e^(−ξ)dξ/ξ
- s,r
- drawdown and distance from well m
- Q
- positive pumping volumetric rate m³ s⁻¹
- T
- transmissivity m² s⁻¹
- S,u,ξ,W
- storativity, integral argument/variable and well function 1
- t
- time since pumping began s
Conditions and scope
- Q>0 begins at t=0 from a uniform initial head; t>0,r>0,T>0,S>0. Use a horizontal homogeneous isotropic aquifer of uniform thickness and effectively infinite extent, full penetration, negligible well radius/storage, no leakage/recharge and elastic storage.
- Boundaries, partial penetration, variable pumping, delayed yield, leakage, heterogeneity and well losses need adapted solutions. Fit residuals and parameter covariance do not certify geological validity or sustainable long-term yield.
Sources · 1
References
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Evidence and review
Read actual integral definition, aquifer/line-source assumptions and sensitivity/fit explanation. Corrected the HTML's swapped s/S equation typography using its explicit symbol definitions; retained no old FORTRAN implementation, numerical approximation or claim that least squares is automatically unbiased. Constant-start/zero-far-field/source conditions are explicit for this standard solution, whose governing PDE is independently checked by substitution.
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Entry details
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- uni-earth-theis-well-drawdown
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- University core expansion