flow structures (option 14)

[ocampero]

Hi Chris,

My model has two ponds (upper pond and lower pond) one next to the other. The bottom elev for the upper pond is 1247 m and for the lower pond is 1242 m. The top elevation of the earthen embankment that divides these two ponds is 1250 m. There is also an emergency spillway in the upper pond that discharges into the lower pond. I want to simulate a breach of the embankment. I have as input the inflow hydrograph and pond volumes for both ponds. The floodwater will eventually fill the lower pond and then continue to the downstream channel (approx. 3 km) I'm using DAMBRK option 14 for this model. One of the potential problems is that the inflow hydrograph is very low and that the model requires a "fake" flow at each flow structure.

Questions are:

1) If I compensate this fake flow by adding it to the inflow hydrograph, up to which point should I stop adding it if I don't know the time when the dam will breach?

2) Do I need to have a minimum channel distance between flow structures? In my model they are just one next to the other divided by an embankment that will be breached eventually

3) Do I need to declare a fake a flow at each flow structure every time?

4) How can I take into account the inflow hydrograph for the lower pond in the same system? Option 14 only allows to use the inflow hydrograph at the most upstream flow structure only.

Thanks,
OC

[Chris Maeder]

Dear OC:

Note that DAMBRK will model it as a single system. Therefore, you need to define the desired model flow at the upstream reservoir, and then the routing will take that inflow all of the way downstream.

You can try increasing your base flow for the upstream reservoir inflow hydrograph, and then to route that larger base flow into the next downstream reservoir, specify this larger flow for the "Turbine (or Other)" discharge value for the upstream reservoir.

I don't think that you need to worry about a minimum channel distance between the reservoirs. You can specify as short a distance as you want.

Sincerely,

Chris E. Maeder, M.S., P.E.
Senior Technical Engineer
chris.maeder@bossintl.com