Cathy Ryan and Jerry Osborn

Transcription

1 Geoscience, Faculty of Science The Role of Groundwater in Flooding Cathy Ryan and Jerry Osborn CWRA (Calgary) March 25,2014

2 Groundwater and flooding

3 Groundwater Resources in the Calgary Area (Meyboom, 1961)

4 Cantafio, 2012 Typical vertical cross-section

5 Alberta flood mapping Flood Hazard Area: The flood hazard area is typically divided into floodway and flood fringe zones and may also include areas of overland flow. Floodway: The portion of the flood hazard area where flows are deepest, fastest and most destructive. The floodway typically includes the main channel of a stream and a portion of the adjacent overbank area. New development is discouraged in the floodway. Flood Fringe: The portion of the flood hazard area outside of the floodway. Water in the flood fringe is generally shallower and flows more slowly than in the floodway. New development in the flood fringe may be permitted in some communities and should be flood proofed. Overland Flow: Areas of overland flow are part of the flood hazard area outside of the floodway, and are typically considered special areas of the flood fringe.

6 Alberta flood mapping

7 Alberta flood mapping

8 Alluvial aquifers river-deposited usually under and on at least one side of the river can be highly permeable (esp. in upper reaches) lattice-like [gravel] substrate ; stream insects found up to 2 km away from river (Ward and Stanford, 1988) can have significant water exchange between groundwater in the alluvial aquifer and the river gw flow tends to be sub-parallel to river can be effectively mapped using air photo interpretation, geotechnical & water well logs, and till ground truthing glacial alluvial aquifer bedrock (not very permeable)

9 Bow R Alluvial Aquifer in Calgary Cantafio, 2012

10 C. Greene, A. Roome-Sandrin, T. Simieritsch, M. Towey

11 Flood 2005 lessons learned (ENSC502) Overland flow only accounted for 17% of the total damage reported by residents Underground seepage (not overland flow) responsible for most of flood damage Setback only moderately appropriate for minimizing damage Ground elevation was as predictive of damage as distance from river/floodway (50% of damage occurred to homes with ground elevations <3.0m above the river (90% to homes with ground elevations >3.7m above river)

12 A better approach to regulation (ENSC502) Regulate basement depths with respect to river stage and water table elevation consider zoning areas based on basement elevation above the 1:100 year river stage (and groundwater level)

13 2013 ENSC Field School project on Flooding in Redwood Meadows

14 ENSC501 Field School II, 2013 co-researchers N. Chin, A. Chung, L. D'Silva, M. DeCock, D. Doerksen, R. Donais, T. Fairfield-Bilyk, A. Grant, P. Jones, S. Karim, A. Kerford, A. Klein, J. Kolodziej, E. Kordich M. Kovacs, L. Laframboise, G. Lam, B. Linaker, R. Lorimer, A. Ma, K. McGeary, K. Moreira, S. Muminovic, T. Paradis, G. Perepelkin, A. Pulwicki, T. Rajabi, M. Revay, N. Rider, S. Ross, J. Sekhon, A. Smillie, S. Spaho, K.Stuart, K. Sutcliffe, M. Tang, E. Timmins, E. Webb, L. Wonneck and N. Taube, H. Jabusch

15 Provincial flood maps

16 Flooding in RWM homes Number of responses Clear Dark Odourous Non-Odourous Other 0 Characteristics of the water that entered the house?

17 Flooding in RWM homes Number of responses Sump pump Floordrain Foundation and cracks Others Where do you suspect water first entered your house

18 Flooding in RWM homes

19 Flooding in RWM homes

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21 Water level responses in alluvial aquifer measured river stage

22 Water level responses in alluvial aquifer Role of paleo-channels?

23 Role of paleochannels in gw flooding Tonina and Buffington, 2009.

24 What does groundwater flooding look like? ICLR, 2009

25 How does groundwater enter homes? ICLR, 200

26 What does the scientific literature say? Groundwater flooding is poorly understood, often confused with surface water flooding, and has not been widely recognized as a problem, either in the UK or internationally. Hughes et al., 2011

27 Groundwater monitoring wells tools of the trade Well Cluster Nested Wells Monitoring well casing Individual drive-point or drilled monitoring wells Sand packs Bentonite seals Screened intervals Large hole 14-27

28 Conclusions gw inundation can significant basement floor elevation w.r.t river state is relevant can look like sewer back-up paleo-channels might be important Field investigation, gw monitoring wells needed