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  1. chaa

    PMF Equation

    It seems to me that the 5-point distribution PMP can be utilized in determining the PMF for small watersheds (10 mi2 or less). I assume that PMP6 (6 hour PMP) in the equation can be read directly from Figure 18 (D.A.=10 mi2) of the NOAA/ACOE Hydrometeorological Report 51 (if east of 105th...
  2. chaa

    PMF

    Thank you for the answers.
  3. chaa

    PMF

    Is anybody familiar with a method of calculating the probable maximum flood? It's a dam site in New York State, Putnam County. I was able to locate a "rule of thumb" procedure used in the past (30-40 years ago) in the ACOE Phase 1 dam evaluations but I'm not sure if it's still valid. I will...
  4. chaa

    HEC-RAS Question

    I appreciate a lot your effort and the time you guys spend in trying to help. The flow regime at the immediately downstream section is also subcritical and the water surface elevation does not change between the two models (before and after improvements)- the water surface elevations are...
  5. chaa

    HEC-RAS Question

    Thank you all. Francesca, I understand what you said, but...Does it mean that in most cases when you increase a waterway cross section you reduce velocity and increase water depth? For uniform channels doesn't happen. As a test, I used an old natural waterway (brook) HEC-RAS model and at two...
  6. chaa

    HEC-RAS Question

    By increase of cross sections I mean a new sream alignment; excavating the channel at one of the banks. This is because the structural engineer would like to eliminate/reduce a flow impact area.
  7. chaa

    HEC-RAS Question

    Sorry. I mean, reply.
  8. chaa

    HEC-RAS Question

    Thanks Rookie2 for the replay. The flow regime is subcritical in both situations.
  9. chaa

    HEC-RAS Question

    I'm doing a waterway analysis using HEC-RAS. An increase of the channel crosssections in a certain reach of the stream leads to lower velocities but an increase of the water surface elevations. I can't really explain why the water surface is higher. Can anybody help? Thanks.
  10. chaa

    Flood Routing Question

    Thank you both. The situation is very close to what Francesca described. I made the condition quite unusual because I was trying to calibrate the model to some known discharges. Calibration is tricky...we have to be very carefull.
  11. chaa

    Flood Routing Question

    Thank you Francesca. The remaining 3 sq. miles is to the mouth of the watercourse. The model covers the whole watershed. Yes, I'm modeling as you are suggesting and the schematic shows it. It's my understanding that "is quite typical for the peak flow reduction of a dam to be lost more and more...
  12. chaa

    Flood Routing Question

    I'm modeling an 11 sq. mile watershed using WinTR-20 for the first time. The drainage area at an existing dam is 6 sq.mile. Approx. 1,500 feet downsream of the dam there is highway crossing A (D.A.=7 sq. miles). Approx. 6,000 feet from highway crossing A there is another crossing, let's call it...
  13. chaa

    CalibratingWinTR-20

    Thanks RWF7437. The article is pretty general but I'm sure I'll learn something.
  14. chaa

    CalibratingWinTR-20

    Please, does anyone know how you calibrate a WinTR-20 model for known discharges (developed from gauging station records)?
  15. chaa

    Detention in lower sections of a watershed

    It appears that detention basins located in the lower sections of a watershed are not necessary. They might even be detrimental because of peak discharge increase. For a 12 square mile watershed what kind of analysis can be performed in order to identify the lower section of the watershed where...

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