The Water Beneath Our Feet: Understanding the Groundwater Resource

Transcription

1 The Water Beneath Our Feet: Understanding the Groundwater Resource Kerry MacQuarrie Department of Civil Engineering & Canadian Rivers Institute University of New Brunswick Fredericton, NB

2 In a 1904 decision, Houston & Texas Central Railway v. East, the Texas Supreme Court refused to protect adjoining landowners (from the effects of pumping) because it thought that the principles that control the movement of groundwater were: "so secret, occult, and concealed that an attempt to administer any set of legal rules [would result] in hopeless uncertainty, and would, therefore, be practically impossible." Source: R.J. Glennon, 2004, Water Follies: Groundwater Pumping and the Fate of America s s Fresh Waters

3 Presentation Content 1. Some groundwater basics. 2. What are the hydrologic flow implications of groundwater extraction? 3. Groundwater and stream temperature. 4. Where are we now (it s not 1904 and we are not in Texas!)

4 Groundwater A water resource (renewable, or non-renewable?) that is: Widely available Generally of good quality Relatively inexpensive In many parts of the world there is no alternative to groundwater for meeting freshwater requirements.

5 The Global Hydrologic Cycle Source: Adapted from the United Nations Environment Programme

6 The Importance of Groundwater Globally, groundwater plays a central role in agriculture for example, 70% of all groundwater extracted in the US is used for irrigation. The natural discharge of groundwater also supports ecosystems (streams, wetlands, etc.).

7 The Importance of Groundwater Almost 10 million Canadians use groundwater for drinking water. Water supply for over 80% of Canada s s rural population. Especially important in PEI.

8 Aquifers are the geological units that transmit and store groundwater. They can be small, large, shallow or deep. Residence time of groundwater in aquifers can vary from years to millennia. Source: Council of Canadian Academies, 2009

9 Base flow index (BFI) = base flow stream flow Source: Grizard, in preparation

10 Source: Danielescu et al., 2009 Groundwater is typically cooler in summer than surface water (and warmer in winter).

11 Groundwater Extraction by Pumping

12 Pre-development Recharge Discharge aquifer Groundwater extraction Recharge (unaffected) Extraction Discharge

13 Groundwater Extraction Pumping wells first draw water from storage draining water from the water-filled pores and fractures close to the well. Then gradually begin to capture groundwater flow that would normally discharge to surface water. If pumping rate/duration is high/long enough, may reverse flow direction and induce surface water infiltration into the aquifer.

14 Source: Barlow and Leake, 2012

15 Groundwater Extraction When aquifer storage is no longer a source of water to the well(s), then all of the pumped water must result in decreased stream flow either by captured discharge or induced infiltration. But, it takes time for full stream depletion to occur (and it takes time to recover after pumping stops). Distance of well(s) from stream, aquifer parameters, pumping pattern, all play a role.

16 Groundwater Extraction hypothetical well 350 m Assumed some typical PEI aquifer hydraulic parameter values (need to know these values to make calculations).

17 Groundwater Extraction Cumulative impact of multiple pumping wells can be significant (and so must be assessed/managed). Consider the history of irrigation in western Kansas (semiarid climate; but overlies one of the major aquifers in North America).

18 History of groundwater allocation and rights in Kansas Source: Sophocleous, 2012

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20 Groundwater and Stream Water Temperature

21 Groundwater Temperature Annual groundwater temperature fluctuations are relatively small, so groundwater discharge provides a stable temperature environment for fish and other aquatic organisms. Source: Bartlett, 2011

22 If the groundwater discharge is localized, then it may also create thermal refuge for fish species during warm water events. Example from a New Brunswick river: Flow Source: Wilbur, 2012

23 Groundwater Temperature Groundwater pumping may cause stream temperatures to increase during the summer, but there is a lack of empirical evidence to determine the magnitude of such increases. Source: Barlow and Leake, 2012

24 Data from a small stream (Otter Brook) in central New Brunswick: Confluence East Branch West Branch Source: Somers, 2013

25 Source: Somers, 2013 June 2010

26 Effect of a hypothetical reduction in base flow of ½,, applied to each base flow location (reduced total groundwater discharge to brook by about m 3 /sec or 1000 igpm). Source: Somers, 2013

27 Summary

28 Summary The hydrologic understanding and methods used to evaluate groundwater-stream interactions have progressed significantly in the past 10 to 20 years. The extraction of groundwater should be expected to have some impact on surface water; the magnitude of the impact will depend on the nature of the pumping and the aquifer/stream properties. With information (data), there are tools than enable forecasts to be made.

29 Source: Council of Canadian Academies, 2009

30 Sustainability Goals for Groundwater Source: Council of Canadian Academies, 2009

31 An aquifer is like a milkshake glass and each well is the equivalent of a straw in the glass. What most countries permit is a limitless number of straws in the glass. This is a recipe for disaster. R. Glennon, University of Arizona, 2012

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