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Thank you Peter, for your answer. Much appreciated, Denise

If the local water board wants the runoff to be held for any length of time before discharging, then that sounds like a detention pond. If that is the case, then you would need to use the SCS method (Curve Numbers for the cover of the land)because time is now involved rather than just the peak...

I am reviewing an engineer's drainage report, showing both current and proposed conditions for a housing addition. In the proposed design, a detention pond is designed, with an outlet structure. The details are shown in the accompanying file. To figure the discharge at the elevations, would I...

All, I had to read each of the answers three or four times to understand the intent! The total of the impervious areas (roofs and driveways) came out to be 6.6% of the total drainage area, or 0.25 acres. So....since that is less than 30%, an adjustment would have to be made. By the way, the...

Thanks, Kevin. Your answer makes sense. I think I'm thinking too hard about this; I tend to do this! [ponder][hammer]

Say I have a pre-construction site which has a total area of 3.8 acres. In this 3.8 acres lies two homes (about 1400 sf - one floor), two separate garages (not connected to the homes and about 450 sf each) and a small shed. The rest of the acreage is grass, in good condition. When the runoff...

Hello, I am struggling with HEC-HMS, particularly with Control Specifications and Time Series Data. I don't understand what they are and how to configure them so I don't keep getting errors after errors. [banghead] As far as the time series data goes, my predecessor told me to use the Type II...

I appreciate all who answered my questions. Thank you!

Hello, I am reviewing drainage which has a detention pond with the outlet structure as shown on the accompanying file. The outlet structure is a 4' x 4' Riser Box. The top elevation of this box is 1300, while the bottom elevation is 1295.30. There are two circular openings on one side of the...

hello all, I am reviewing a proposed construction site's drainage report. Included in it is a detention basin to capture the water after construction, slow it down and then take it to the ditch of the adjoining state highway. The parking lot area of the proposed construction site has a storm...

Thank you very much cvg. Quick and down-to-the-point answer!

Hello, In reviewing a detention basin with a single outlet structure being that of a 18" pipe with no riser attached, how do I analyze the pipe? I'm wanting to use this analysis to put together a table with elevations and discharges of the pipe. Would I analyze it using HY8 or using Orifice...

Thank you everyone, for your response. Tailwater will only occur if there is higher flows; fortunately, discharges will not get that high, so the pipe is operating with much less tailwater. I'm going to charge forward using the v-notch weir, now that I won't have to worry about tailwater...

Hello everyone, The detention basin has an outlet structure of a 3' x 3' box, with a V-notch weir on the entrance side and a 12" RCP stubbed into the opposite wall. I work with HEC-HMS. The pipe has a very flat slope (0.26%); it has tailwater. How would I figure the discharge going through the...

Thank you SMIAH and GBAM. I think I'm going to analyze the pipes in Modified Puls Method, similar to a Reservoir Routing. Come up with a stage-storage and stage-discharge tables/curves and Inflow hydrograph and use them to come up with the outflow, based on the configurations of the pipes...

hello, I've only been using HMS for a little over a year now, so I may not have come across this in the program yet. I have a drainage area flowing through a double 24" RCP. Can I analyze the RCP as a reach in HMS? Once the water flows this double pipe, it combines with water which has flowed...

Thank you Twinkie. I appreciate your time and knowledge.

Hi Twinkie, By the greater-than sign, do you mean for me to route the water through the toewall first, then through the weir? Thanks!

Hello, I use HEC-HMS to route water through a detention pond. To find the elevation - discharge curve, I use Excel to find the discharge relating to its relevant elevation - using the Weir or Orifice Equations as appropriate. I'm working on a detention pond that has a 4' wide by 45' long...

I'm fairly new to the Dam / Reservoir hydraulic modeling, so I'm sure there a million questions zooming around in my head, but, for now, I have just a couple. I'm working on a Dam that was built in 1967. Before the previous drainage engineer retired, he told me to use the sediment pool...