Wetland Pond Design

[WILDWINGS27]

I am designing a wetland style pond and need to keep the total water inundation time under 72 hours during a 100 year event in order to not kill the plants. The site is about 10 acres and the pond is only about 2-2.5' deep. Using TR-20 with a Huff rainfall distribution, my total time is over 80 hours. Is their anything I can do to lessen the amount of time water is in the pond?

 

[cvg]

make the outlet larger?

 

[WILDWINGS27]

I can only release 0.15 cfs/acre. I am already at that in my design.

 

[cvg]

put in a dry well

 

[Drew08]

Do you need to drain the entire 100-year storm stage in 72 hours, or just down to some stage that floods more often and contains hardier plants?

What kind of hyper sensitive wetland plants are you using that won't die if flooded for 72 hours every 100-years, but will die if flooded for a mere 8 hours longer every 100-years? It seems an arbitrary line in the sand. Perhaps the risk, and potential replacement costs, of some plants dying in the event of the 100-year storm is worth avoiding the added cost of a floodplain study, or culvert replacement project downstream.

What is the factor limiting the design discharge?

 

[francesca]

I'd be more worried about a 10-acre site not being able to maintain a level of inundation to support wetland plants. Obviously it depends on climate, but where I am the minimum for a wet pond is 20 acres.

 

[sammyk]

You'll never be able to design the pond to drain below 72 hours and meet your release rate. Your wetland pond should be planted with wetland style plants which will be water tolerant to a point.

But even if that point is reached the wetland style plants will establish a "seed bank" which will allow renewal of the wetland plants when conditions are better.

When you say you are designing a wetland style pond, do you mean that you will be planting "plugs" in a 6"-12" depth wet-bottom or seeding a dry bottom basin with wetland plants?

Just as a curiosity, why did you design your pond with only 2-2.5' of bounce?