Question: Does groundwater affect optimal population size?
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Transcript of Question: Does groundwater affect optimal population size?
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Question:
Does groundwater affect optimal population size?
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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
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saprolite
Fractured bedrock
alluvium
water table
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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.
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sustainable groundwater management:
non-extractive groundwater services
receive primacy over
extractive groundwater services
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or…(maximum sustainable extraction
volume) equals
(volume of groundwater supplied by recharge)
minus
(volume of groundwater required to support non-extractive services)
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How do we quantify non-extractive groundwater
services?
percentage of impervious land cover
is a proxy for
degradation of non-extractive groundwater services
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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.
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a community’s sustainable population size is determined, in part, by
availability of sustainably managed groundwater
…not byavailability of groundwater for
unthrottled extraction
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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)
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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