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  1. froude

    STORMCAD MODELING

    Could you not simply model it as a conduit of very short length with a slightly smaller height than the adjoining sections?
  2. froude

    HEC-HMS Modeling Help--Rectangular Weirs

    One option may be to specify a "Dam Top" for your reservoir with a Non-Level Overflow method. You can then specify a cross-sectional geometry of your structure. Another option would be to develop an elevation-discharge rating curve for your structure and use that as your outfall structure. I...
  3. froude

    Pond Storage Volume: Hydraflow vs. PondPack

    Hello All, I am trying to reconcile why, when using the same Modified Rational parameters, Hydraflow (Autodesk) and PondPack produce starkly dissimilar pond storage needs (Hydraflow calculates only half the storage need that PondPack calculates). Both programs seem to use storage-indication...
  4. froude

    Change Time Interval in Paired Data of HEC-HMS

    Bill, You might be able to use a Discharge Gage in the Time-Series data which will allow you specify the time interval of your choosing and specify the associated discharges. Hope this helps. Good luck.
  5. froude

    Estimating impervious cover for a large (~20 square mile) watershed

    It looks like a bevy of data is available through https://data.georgiaspatial.org/. This includes quad maps, imagery, soils, among other things.
  6. froude

    Estimating impervious cover for a large (~20 square mile) watershed

    QuantumGIS (QGIS) is an open-source GIS platform that is available for free. We have access to ESRI licenses at work, so I haven't tinkered with QGIS much. But from what I hear, it is very comparable and, well, free. I believe that 10-ft interval USGS topography can be downloaded for free or...
  7. froude

    HEC-HMS 3.5 and Multi-stage outlet stucture capabilites??

    You may be able to just do a regular Excel (.xls or .xlsx) spreadsheet and copy/paste the values into your HEC-HMS reservoir element.
  8. froude

    Design of Storm Water Structure

    It's hard to fully visualize the situation without a plan & profile, but here's a few thoughts... Regarding going over the gas main: I don't know what your municipalities clearance requirements are, but if the gas main is only 3' below the pavement, your proposed 12-inch storm drain line may...
  9. froude

    widen bridge vs detention

    Is the reviewer requesting it from a water quantity or quality standpoint? Is this a private development or a municipal/state/federal job? I don't know all the specifics/forensics/history of your project, but it seems stringent to require detention for what you are describing from a runoff...
  10. froude

    Modeling Diversion in HEC-HMS

    Rookie2, It sounds like you may be able to utilize the "Auxiliary Discharge Location" feature (see HEC-HMS User's Manual - Chapter 9 Reservoir Elements). Using this, you will be able to model both the riser and the weir with flow from the riser going into your downstream pond element and flow...
  11. froude

    Working out Flow through a stormwater pipe with only top water level known

    If it were just a culvert I would suggest using one of the FHWA nomographs. Since it's an entire network, my thought would be to set up a model of your network (in StormCAD or similar) which includes all your pipes, junctions, and appropriate losses. Then (I'm assuming you only have flow...
  12. froude

    Help - cannot copy basin file and got warning below. Any ideal to resolve it?

    It sounds like the folder that your basin file is located in may be write-protected. If that's the case, you can probably go into the the folder's properties (through windows explorer) and uncheck the read-only option.
  13. froude

    Detention Ponds and WSE

    Victoria, 1. Do you know which type of hydrologic method you will be using? Will it be a unit hydrograph? Modified Rational? This is something you need to know ahead of time and may be dictated by your local municipality or reviewing body. 2. Do you know what your target release rate is...
  14. froude

    RCP Wall Thickness and Weight by Class

    Hanson Pipe and Precast has technical specifications that can be downloaded as a PDF. I believe you'll have to create a login account (free) before they will let you download.
  15. froude

    LOMR - Duplicate Effective

    Rye1, Unfortunately, I've run into this situation a few times. In one instance, I was able to prove to the local reviewer and the FEMA reviewer that the FEMA library was unable to provide an effective model (I did this by documenting correspondence with the FEMA library in which the library...
  16. froude

    FEMA culvert freeboard requirements

    Yes, I believe all of what you said is correct. It may be that the levees end up having such a big impact on overall flood risk and flood insurance that FEMA has incentive to regulate those more stringently. Plus it could be a game of numbers - there are probably exponentially more culverts...
  17. froude

    FEMA culvert freeboard requirements

    SLOCivil, According to FEMA/NFIP the FF has to be at or above BFE (based on FIS flows or similar). That is just the minimum requirement. I don't believe that there is a requirement for culvert freeboard. Most local municipalities (in my area, anyway) enforce stricter measures (i.e. FF...
  18. froude

    HEC-RAS 4.1 / Check-RAS

    I can't speak towards the use of CheckRAS, but when I get the schematic errors, I usually save the project over to a different name and it starts working (most times). Hopefully that may work for you.
  19. froude

    Encroachments in Hec-Ras

    If you're doing a subcritical analysis, you may want to work downstream to upstream. Some of your downstream encroachment changes could very well affect upstream deltas.
  20. froude

    Encroachments in Hec-Ras

    Unfortunately I encounter this all the time. The HEC-RAS floodway engine is very sensitive and finicky. Even though you set a target rise using Method 4, I don't believe the program iterates enough to relegate encroachments to your specified "maximum." I've noticed that I get very high delta...

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