GROUNDWATER RESOURCES MANAGEMENT IN HARD ROCK TERRAIN: A BALANCING ACT

Robert Earon, Bo Olofsson

Land and Water Resources Engineering

October 12, 2015

Supplying Water in Swedish Coastal Regions

• Traditional reservoirs not common or spatially limited

• While precipitation sufficient to meet water supply needs, shortages occur

• Problem worsened by increasing permanent residency in traditional cottage areas

• Difficulty in connecting some rural areas to municipal water supply

• More than 1 million depend on private wells, either continuously or seasonally

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

Potential ET Precipitation Balance

Outcrop

Clay

Till

Sand

Gravel

What are the specific challenges with implementing a water balance in this type

of terrain? • Parameter uncertainty - Heterogeneity

• Fractured Rock • Distribution/stratification of Soil Cover

• Storativity • Relative to extraction • Limited – soils (till and clay) and rocks

• Recharge • Time scale? Spatial scale? • Regional method?

• Extraction • Fracture system dependent • Preferential pathways?

• Subsurface flows • Homogeneity – Simple and efficient, but wrong • Heterogeneity – Better, but difficult and uncertain

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

Q R

Groundwater Balance

Soil Data

Topography Data

Soil Depth Model

Bedrock Data

Well Data

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

August 40% Permanent residency

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

General water balance (limited storage) (a) compared with spatial water balance (b) from Tyresö.

General agreement between models, extreme values seen towards coast due to low porosity , topography and hydraulic conductivity

(a)

(b)

August 40% Permanent residency

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

General water balance (limited storage) (a) compared with spatial water balance (b) from Tyresö.

General agreement between models, extreme values seen towards coast due to low porosity, topography and hydraulic conductivity

(a)

(b)

• Increased evapo-transpiration (+10%)

• Increased permanent Residency (25% to 60%)

• Impacts not distributed evenly, instead localized to specific problem areas

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

• Water levels estimated based on remaining reservoir and porosity in bedrock

• Low hydraulic conductivity in fractured bedrock leads to local differences in groundwater reservoir between models

• General agreement between two scenarios

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

No Subsurface Flow Subsurface Flow

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

Permanent Residency: 40% 80% 100%

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

Difference between 10 m cell size, 8 month scenarios, (a) 20% and 40% permanent residency (b) 80% and 100% permanent residency

(a) (b)

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

Difference between 80% residencey 8 month scenarios, (a) 10 m and 2 m cell size comparison (b) 20 m and 10 m cell size comparison

(a) (b)

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

Summary

• Method applicable in a GIS environment using existing databases, providing a general overview of existing and future groundwater scenarios.

• Heterogeneity in storativity, extraction illustrates the need for spatial approach

• General agreement with traditional methods, but a more complex picture emerges

• Temporal scale important, where issues appear on a monthly basis which may not be present yearly

• Impacts exist at very low permanent residency rates on a local scale

• Resolution of models influences local results

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS

THANK YOU

INTRODUCTION CONCLUSION APPROACH WATER BALANCE RESIDENCY EFFECTS SPATIAL EFFECTS