About

James M. Wilkinson, Ph.D., P.G.

Senior Hydrogeologist

The work behind this calculator spans more than two decades.

It began at the U.S. Geological Survey, where groundwater modeling of the Portland Basin aquifer system raised a question that proved stubbornly difficult to answer: how do you reliably estimate effective porosity — a fundamental aquifer property — without breaking the budget or the schedule?

Laboratory grain-size analysis and tracer studies can yield defensible results, but they are expensive, time-consuming, and in many field settings simply not practical. For the vast majority of the world’s water wells, that data never gets collected.

Specific capacity — the ratio of well yield to drawdown — is different. It is recorded routinely during well construction at no additional cost, stored in accessible databases in most countries around the world, and almost universally overlooked as a source of porosity information.

The Wilkinson equation changes that. Calibrated on well databases in Oregon, Texas, New Mexico, and South Sudan, it produces reliable effective porosity estimates in seconds, from data that already exists. It requires no additional field work, no laboratory analysis, and no specialized equipment.

The method is not limited to a single geology. Wherever there are water wells, there is specific capacity data — and wherever there is specific capacity data, this approach applies. The goal is to put a tool that was never available, directly into the hands of earth scientists and students everywhere, at the moment they need it.