Question:

Does groundwater affect optimal population size?

Definitions:groundwater services: conditions &

processes through which groundwater provides benefits to human society

extractive groundwater

services:• drinking water• irrigation

• industrial uses

non-extractive groundwater services:• soil moisture for

vadose zone• base flow for rivers &

streams

saprolite

Fractured bedrock

alluvium

water table

Question:

How much groundwater is there?

Answer: Lots! *

* but it’s not evenly distributed & we need to leave most of it in the ground anyway to protect non-extractive groundwater services.

sustainable groundwater management:

non-extractive groundwater services

receive primacy over

extractive groundwater services

or…(maximum sustainable extraction

volume) equals

(volume of groundwater supplied by recharge)

minus

(volume of groundwater required to support non-extractive services)

How do we quantify non-extractive groundwater

services?

percentage of impervious land cover

is a proxy for

degradation of non-extractive groundwater services

5-20% impervious land cover, equivalent to 5-20% reduction in recharge, causes degradation of aquatic ecosystems due (in part) to decline in stream base flow….

80-95% of groundwater recharge is needed to supply non-extractive groundwater services.

5-20% of groundwater recharge is available for extractive groundwater services under a sustainable groundwater management paradigm.

a community’s sustainable population size is determined, in part, by

availability of sustainably managed groundwater

…not byavailability of groundwater for

unthrottled extraction

quantitative example: 1000 acres, EBRF

theoretical recharge available: 1.08 MGDunder sustainable management,

volume required for non-extractive services: 80-95% of recharge (.8 -1.02 MGD)

theoretical maximum sustainable extraction: 5-20% of recharge (.05 – .2 MGD)

theoretical sustainable maximum, entire EBRF:

3.9 – 7.8 MGD (25 – 49% of projected municipal demand at build out)

policy recommendations: adopt principles of sustainable groundwater

management that couple allowable groundwater extraction volumes with protection of non-extractive groundwater services

protect groundwater recharge by limiting watershed impervious land cover & maximizing storm water infiltration

use community wells to serve rural residential development densities greater than 1 house per 2 acres

research recharge and groundwater flow relative to areas of high potential for sustainable extraction

use sustainably managed groundwater to augment municipal water supply in Charlottesville and Albemarle