Calculate the radius of influence for dewatering wells or pumping tests from hydraulic conductivity, drawdown, transmissivity, storativity, and time.

Planning estimates only; neither method defines a sharp groundwater-impact boundary. Use site data and hydrogeologic assessment.

Material suggestions are illustrative; use measured site K where available.

Radius of Influence Formula

The calculator offers two pumping-related estimates: the empirical Sichardt dewatering radius and the extrapolated zero-drawdown intercept of the Cooper–Jacob late-time approximation. Neither defines a sharp physical boundary of groundwater impacts.

Sichardt: R = 3000 × s × sqrt(K); Cooper - Jacob: R = sqrt(2.25 × T × t / S)
  • Where R is the estimated radius in meters
  • s is drawdown at the well (m) for Sichardt
  • K is hydraulic conductivity in m/s for Sichardt; the coefficient 3000 requires these units
  • T is transmissivity (m²/s), t is pumping duration (s), and S is dimensionless storativity for Cooper–Jacob

Choose the method and enter positive site-specific inputs. The calculator converts units before applying the formula. Sichardt is an empirical unconfined-dewatering estimate. Cooper–Jacob assumes constant-rate pumping in a homogeneous, isotropic confined aquifer and uses a late-time approximation; its zero-drawdown intercept is not a true zero in the Theis solution.

What is radius of influence?

Definition:

A radius of influence is an approximate distance from a pumping well or recharge source beyond which the change in groundwater level (drawdown or mounding) is considered negligible or below a chosen detection/impact threshold.

How to calculate radius of influence?

Example Problem:

The following example outlines how to calculate a radius of influence.

First, determine the drawdown for a Sichardt estimate. For this example, s = 5 m.

Next, determine the hydraulic conductivity. In this problem, the hydraulic conductivity is .000005 (m/s)

The Sichardt method does not use a recharge-rate input. Use measured hydraulic conductivity where available rather than treating material suggestions as guaranteed values.

Finally, calculate the radius of influence using the formula above:

R = 3000*s*sqrt(K)

R = 3000*5*sqrt(0.000005)

R ≈ 33.541 m

FAQ

What factors can affect the hydraulic conductivity in a radius of influence calculation?

Hydraulic conductivity can be influenced by several factors including the porosity and permeability of the soil or rock, the presence of fractures or voids, the saturation level of the material, and the temperature and viscosity of the fluid. Changes in any of these factors can lead to variations in hydraulic conductivity, thereby affecting the calculation of the radius of influence.

How does the thickness of the aquifer layer impact the radius of influence?

Aquifer thickness is not an independent input in these two modes. It can affect transmissivity, which equals hydraulic conductivity times saturated thickness for a uniform layer. Sichardt uses drawdown and conductivity; Cooper–Jacob uses transmissivity, storativity and time.

Can the radius of influence change over time?

Yes, the radius of influence can change over time due to variations in recharge rates, changes in hydraulic conductivity due to sediment deposition or erosion, alterations in groundwater extraction rates, or shifts in the hydrological characteristics of the area. Monitoring and recalculating the radius of influence periodically can help in understanding and managing the effects of these changes.