Pond Boss Forums POND CONSTRUCTION Selecting a site Dam break inundation risk models?

Hi all. So I am looking at buying a 6-acre pond that is classified as Low Hazard damn by the state. They are planning to re-assess hazards this coming year and I may pass on it if its obviously going to be put into a higher category. I know there was a house built downstream after it was first rated.

Is there simple damn-break inundation model or approach to estimate flood hazard on dam break based on 1 or 2ft topo maps, height of dam, and volume? its an 8 foot dam, 17 acre-ft storage I think. I realize that an engineering firm would do this, but im looking back of the envelop at this stage. I attached a topo map with 2ft lines- do those houses look obviously at risk? Yes, I know no one can know for sure... no one is getting sued. Just looking for opinions.

In the map, the front parcel with the outflow is 10 acres.

I have no idea. Talk you your counties NRCS office.

Jim,

The last time I looked into dam risk charts it was amazing how little influence a body of water that small would have during any rain event. I had a friend who's dam partially failed during a large rain event (over 10 inches in under an hour). When the engineers finished the calculations for height, resistance, ect, it turned out his water added .1 of an inch to the flooding down stream and extended the duration only 20 or 30 minutes. In short, not his fault or issue. His dam was under 20 feet tall and his dam held back somewhere around 60 acre feet of water as I recall.

Of course, your milage may very. Asking an engineering firm is the right way to cert your dam.

Thanks Brian for your thoughts. Very helpful. It's hard to have time to due all this diligence correctly for a purchase decision Any Idea on the cost range for that analysis?

Not there, he had to pay for a post failure calculation which I believe cost more due to timing. I would bet that with today's access to information(G Earth and all), it would be easier than in the past.

Let us know if you find out the cost and timeline.