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Barometric Efficiency

Barometric Efficiency. The observed influence of barometric pressure (BP) on water levels (WL) Defined using: BE = - WL / BP This method looks at long-term changes of BP on WL Another method accounts for short-term changes BE = - ∆WL/ ∆BP These assume that the response is instantaneous

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Barometric Efficiency

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  1. Barometric Efficiency • The observed influence of barometric pressure (BP) on water levels (WL) • Defined using: BE = - WL / BP • This method looks at long-term changes of BP on WL • Another method accounts for short-term changes BE = - ∆WL/ ∆BP • These assume that the response is instantaneous • Normally applied to confined aquifers • Because surface loading causes aquifer compression • Part of the load borne by water, rest by mineral skeleton • Also see a response due to trains, tides, precipitation

  2. Tidal Efficiency, TE TE = ∆TH / ∆BP = ∆ (WL + BP) / ∆BP = - BE + 1 • so that TE + BE = 1 • Inelastic BE = 1 TE = 0 • Elastic BE = 0 TE = 1

  3. Specific storage (Ss) • Aquifer porosity (n) • Aquifer bulk modulus of elasticity (Es) • Specific weight of water (w) = 9.8 kPa/m • Bulk modulus of water (Ew) = 2.2 GPa • Bulk modulus is reciprocal of the compressibility

  4. Delayed Response • For situations where the response is not instantaneous, we must use convolution: ∆TH(t) = ∑i u(i) ∆BP(t-i) = u(0) ∆BP(t) + u(1) ∆BP(t-1) + u(2) ∆BP(t-2) + where u(i) is the unit response function • Delayed responses occur for various reasons • water table (unconfined) • wellbore storage • dual porosity

  5. Effects of a barometric pressure step increase in an unconfined aquifer Diagram of locations of measurement points 1 and 2 within the well and aquifer, respectively pressure head total head water levels

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