Thursday, July 31, 2014

Raining on our parade?

An earlier posting on My Minnesota noted that the Metro Council's draft Northeast Water Supply Plan didn't yet address water conservation. Another question is whether the groundwater modeling that's being done will take into account the effect on groundwater recharge that's likely to occur over time as the Minnesota Pollution Control Agency's new (completed in 2013) Minimal Impact Design Standards (MIDS) for stormwater come into play.

impervious surfaces generate urban stormwater runoff
Photo by J. Harrington

A key provision, it would seem, is the requirement for
"Nonlinear redevelopment projects on site without restrictions that create one or more acres of new and/or fully reconstructed impervious surfaces shall capture and retain on site 1.1 inches of runoff from the new and/or fully reconstructed impervious surfaces.

"Linear projects on sites without restrictions that create one acre or greater of new and/or fully reconstructed impervious surfaces, shall capture and retain the larger of the following:
  • 0.55 inches of runoff from the new and fully reconstructed impervious surfaces
  • 1.1 inches of runoff from the net increase in impervious area"

precipitation laden storm clouds
Photo by J. Harrington

Over time, might we see sufficient groundwater recharge from following the new standards that, combined with a possible reduction in demand for potable groundwater due to water conservation retrofits, that we have materially affected which options might be preferable as a solution to the disappearing White Bear Lake? Further, do we think it would be helpful to know if there has been an evaluation of the anticipated change in frequency and intensity of precipitation events associated with global warming? A 2008 IPCC report on Water and Climate Change discusses such a pattern change. A 2009 report by the Union of Concerned Scientists on Climate Change in the Midwest notes:
"Precipitation is more likely to come in the form of heavy rains. Under either emissions scenario, Minneapolis-St. Paul is projected to experience a more than 66 percent increase in heavy rainfalls (defined as more than two inches of rain in one day) over the next few decades. Toward the end of the century, heavy rainfalls are projected to be almost twice as frequent under either emissions scenario. The maximum amount of precipitation falling within a one-, five-, or seven-day period is also projected to rise under both scenarios."
Not to seem flippant about any of this, but I'm starting to yearn for the good old days when our environmental issues were as simple as banning DDT and keeping our rivers from catching fire

In addition to the trials and tribulations managing our water properly can create, there's a whole series of very good reasons to better manage our impact on the hydrologic cycle and vice versa. Donella Meadows told us about them back in 1996.

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