Well Sustainable Yield from Specific Capacity
The sustainable pumping rate a well gives up without pulling the water below the pump.
Example
You enter
- Specific capacity (GPM per ft of drawdown) 1
- Allowable drawdown (ft, static to safe level) 30
You get
- Max sustainable yield 30
Details, formula, and sources
max_yield = specific_capacity x allowable_drawdown. A 1.0 GPM/ft well with 30 ft of usable drawdown (static to a safe level above the pump) yields 30 GPM; a marginal 0.3 GPM/ft well with 40 ft yields only 12 GPM. Answers 'how hard can I pump it' instead of the specific capacity from one test. Specific capacity declines with rate, so confirm with a constant-rate test. AWWA A100 / USGS; the well driller governs.
max_yield_gpm = specific_capacity_gpm_ft x allowable_drawdown_ft. The inverse of specific_capacity = discharge / drawdown.
AWWA A100 (Water Wells) standard; USGS well-testing methods (USGS Open-File Report 02-197).
awwa.org for the A100 TOC; pubs.usgs.gov for the USGS report.
Estimate. Operator of record and primacy agency govern.
Field names used by the API: specific_capacity_gpm_ft, allowable_drawdown_ft, max_yield_gpm
- Linear near the test rate specific capacity declines with rate (well losses); the linear yield holds near the tested rate, overstates it far aboveUSGS / AWWA field practice
- Specific-capacity floor < 0.5 GPM/ft flagged as a marginal wellAWWA A100 / USGS field practice