Comment 32592

By Another Hammerite (anonymous) | Posted August 05, 2009 at 16:52:30

I knew the RHVP would cause problems when I thought about childhood experiences of the valley and the creek. There were deep valleys between Albion Road and the ravine where the creek ran, and those were also part of that system and its floodplain. Those are now paved over. The soil there, as indicated on the geological maps, was very sandy. There were small marshes scattered across that sandy soil. In fact there were sand dunes in a few spots, under the grass. This was nearer to the escarpment. Water used to follow that system, but mostly it would disappear underground, into the porous sandy soils. You could watch the magic of its disappearing. The creek itself entered its lower valley which was also partially filled with sandy sediment, washed down from higher ground. That too was porous, and although Albion Falls was a rushing torrent, low and behold, by the time you got to King Street, there was much less water visible. Where had it gone ? Into the sandy soil, the porous accumulation of millenia of creek activity, beneath the more obvious little stream. Now, shove that little stream into a concrete pipe, thinking you have enough pipe based on surface flow characteristics, even if carefully measured year round. No. That isn't enough. You have now stopped the water from entering that porous sandy soil and the UNDERGROUND portion of the stream is now having to move above ground through the manmade pipe and channels. If the water can get there. Some can and some cannot.

The computer model used to determine the engineering of the new water course could not possibly have taken into account the many square kilometers of underground stream activity. It is the underground, invisible, Red Hill Creek, that carried MOST of the water, not the visible little trickle that danced its way across the top and under King Street.

Similarly it is unlikely that the calculations for the visible stream were supplemented by the massive amounts of water underground from its tributary system of sand dunes, flood plain, and little marshes nearer to Albion Road. That was not likely taken as being "Red Hill Creek" proper. Unfortunately that _is_, or rather was, a major part of the Red Hill Creek system.

It is very sad when excessively simplistic calculations are used to model such complex systems, that in reality includes groundwater flow, soil characteristics,... a hydrogeology that is far beyond the limits of the modeling system. Now, did anyone actually construct a scale model, to test flow effects in the redesigned valley ? Not likely. It's very expensive and even that is fraught with risk due to crude approximations.

Expect more floods.


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