Stormchaser wrote:
Would have been an non-issue if the rest of the site was graded such that an overflow didnt reach the building...
I think you can compare this kind of spiked water flow to high voltage electricity, aka lightning. Normal rules don't apply anymore. A single coil becomes a huge inductor. Normal insulators, when more conductive than the surrounding material, become conductors. Heat rises to vaporization temperature in milliseconds. Explosions from steam or other vapor pressure occurs at the conductance path.
Velocity is going to be a factor if a clog occurs, heck, it's a factor without a clog. Water will have the kinetic energy to flow uphill quite a ways at a clog site. To grade the entire area for this scenario would make the schlep around KBL way worse than it is now, as dikes would be in your way.
I watched a pond wash away in hurricane leftovers when the dam failed a while back. The outlet stucture was sized correctly for maximum flow, and it would have been fine given the amount of r*in, except it got clogged with sticks and leaves and no one thought to check it/clear it. The water rose until the earthen dam was breached and after that it went very fast.
My point here is that in peak r*in events you need to plan not only for the peak water flow, but for the trash that gets washed into the culvert opening obstructing the flow. The opening must be many multiples larger than the expected trash debris, ie large branches should be able to pass through KBL's culvert.
I don't think the design of running the culvert under the lodge was necessarily a bad idea. It might be the best thing for that spot to do it again, as an open channel would really impede the kind of congestion that occurs around KBL, both front skier traffic and rear car traffic. (Or whatever side is considered the 'front' of KBL). Imagine how annoying it would be to have a two lane bridge over an open channel where the busses now unload, or in front of the first aid entrance.
A big box culvert would be a better idea. Better still is a second pipe with an invert higher up than the primary that is only used for emegency overflow. That way most trash is collected at the lower culvert, and the emergency pipe can pass spiked flow. If memory serves, the old pipe looked to be 30 or 36 inches.
If this is a once in several hundred year storm, I'd think it's worth it to risk damaging the lodge again in a few hundred years, rather than compromise the best traffic flow design that you live with year in year out, day in day out.
Prior to '79 I didn't think tornados hit new england. Prior to 2011, I didn't think flash floods hit Vermont. Structures that have stood for 200 years were washed away. We are living through historic times.
