Groundwater 101 – The City of Calgary’s Flood Mitigation Strategy


Groundwater is essentially the flow of
water through interstitial spaces in the soil so the spaces between
various soil particles During a flood event as the river rises you’ll also have the driving
head for groundwater it forces the water from the river into the floodplain
soils and eventually it rises as well so it rises in response to the river rising Groundwater is important
because it can enter basements Basements are not impermeable they’re not meant to hold out water so
naturally groundwater if it’s elevated it will enter the basement and that’s
why sump pumps are extremely important and effective because they collect
that groundwater preventing it from rising above the floor
of the basement It’s also important to have
an alternate power source for your sump because in a flood event it’s very
likely that the power will be turned off A flood barrier will reduce the risk of
groundwater flooding in three ways The barrier will actually help to lower
groundwater levels and this is because part of the barrier will be sunk into
the ground and the groundwater will have a longer path to flow across the barrier The barrier protects against groundwater flooding also by blocking overland flow
and overland flow seeps into the groundwater contributing to raising
the levels and also extending the propagation of the groundwater All things considered, this depends on the
makeup of the soils and its characteristics It also depends on the magnitude of
the flood event as well as its duration This will determine how high the
groundwater rises during a flood event For flood mitigation projects, this would be
confirmed through the design process The barrier prevent flooding due to
sewer backup so in many cases and this was a case in the 2013 flood
the flood waters make their way through into the sanitary system as well as a storm system
and that quickly overwhelms it and causes it to rise and the lowest point for it to rise
into is people’s basements and in fact during the flood the majority of basement
flooding was as a result to sewer backup so that’s a flood mechanism that will be
prevented from flood barrier on land During the conceptual design process
we use generalized soil types and layouts to estimate what the groundwater
response might be and what we found was that there is a chance for some groundwater
flooding but the benefits of blocking overland flooding far out way the residual
risks if you will from groundwater flooding so that was enough to understand that there’s significant value to the project During the design process get a better understanding of the
groundwater problem get more site-specific information and
investigation and reassess that those findings For more information on groundwater,
go to calgary.ca/floodinfo
and click on the understand section

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