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thanks beej67. I used these depths to develop an IDF curve that I can use. I was hoping to be able to come up with an equation for use in our spreadsheets. I did some more research and realized that the coefficients from the equation were derived from the curve using Excel Solver, which I...

I'm trying to develop an IDF curve for Craig, Colorado. I'm using the UDFCD Rational Method spreadsheet and have the appropriate 1-hour rainfall depths but I can't seem find the appropriate coefficients for the Rainfall Intensity Equation (a, b, and c). Is there an adjustment factor or a table...

Is there a way to analyze a simple storm system for a user defined peak flow in Autodesk's Storm and Sanitary Analysis? If not what program (preferably free) would you use? I used to use Bently's stormcad for these quick calcs but we decided to drop the license. Thanks

Yes, very helpful. I was able to back into an impervioussness of about 60% Thanks!

What percent impervious/runoff coefficient would you use for the Rational Method for an area that has just been re-graded and probably has hydromulching or something similar but no actual vegetation yet? Also has steep slopes. I'm using 5% for undisturbed areas and was thinking 30% was...

Yes, you are correct, the floodway is the distance between the vertical black lines. Sounds like you're getting there

Thanks for your responses. I talked with a manufacturer who said that they used to make pre-fab flumes larger than the 20-cfs size but found that they were having to encase them in concrete anyway so now they recommend a custom concrete flume for anything that large. For this case I've...

I'm a little late on this but maybe it will help you in the future (or others with the same questions). You say you're not seeing anything - I'm assuming you're looking at the Cross-section window. First, make sure you're showing the correct "plan" (right click and select "Plans"), also, make...

I've always used a 0.2-ft drop in invert across a manhole as a rule of thumb. This corresponds to a theoretical 0.5% slope across a 4-manhole. The only time I've matched the crowns is when the pipe changes to a larger size (our municipality requires this for wastewater and I've just followed...

Any flume experts out there? I'm using WinFlume for the first time to design a ramp flume for an irrigation ditch intake. I'd be very grateful for some peer review of my design (see attached WinFlume file and output pdf's). The existing ditch is between 3'-4' wide at the bottom...

Anyone know where to find the Comparison of Nine Uncalibrated Runoff Models to Observed Flows in Two Small Urban Watersheds, (Zarriello, P, 1998) paper referred to in earlier posts? The links to the USGS page are no longer valid and a general google search has been getting me no-where.

I did - NSS=National Streamflow Statistics. I got 137-cfs, compared to 400-cfs (FEMA), and 812-cfs (new studies PCSWMM)

Thanks for your responses. I am looking into the FEMA regression equations more. The reason I'm so concerned is that the community has been using the FEMA flows for design of several major infrastructure projects in recent years and this new study indicates that they are all undersized and...

A little bit of background... I'm doing a peer review of a Stormwater Masterplan by another consultant. The watershed has ten sub-basins, six of which are included in FEMA's FIS for the region, meaning there are published peak flows for the 100-year flow (I'm focusing on the 100-year peak flow...

Just like sam74 said, you can use DEM files for USGS maps. I found this post a while back that tells you exactly how to find them and use them. I refer to it everytime I need to delineate large basin, which is a lot lately for some reason...

Thanks TerryScan - I hadn't found that you could change the energy dissipator. Also, you're right about the manning's n - thanks for pointing that out. I always feel that the recommended d50 is too small (4"!?). Anyone else have any thoughts on that?

Proposing a 60" culvert at an access road crossing of an intermittent creek on BLM land. Used HY-8 to analyze the culvert (file attached). Now I'm looking at outlet protection. The design flow is 54-cfs (10-yr storm) but want to protect against the velocity for 129-cfs (25-year storm). The...

I'm designing an 8'x4.2'' open bottom arch culvert to be used in a stream with a 100-year flow of 147-cfs. I'm using HY-8 for the culvert analysis - a HEC-RAS model is beyond the scope of this project. The footers for the culvert have to extend about 4.5-ft down to get below frost depth and...

I'm working with a FEMA effective HEC-RAS model that uses contraction and expansion coefficients of 0.6 and 0.8 instead of 0.3 and 0.5 at some culverts. Chapter 5 of the manual shows that these values are used for "abrupt transitions". I have always thought that you used 0.3 and 0.5 for...

Running CHECK-RAS version 1.4 for the first time and have followed all installation and setup instructions to the letter. When I get to the extract data step I get the "Error: data extract" error message (I do not get the "checkras id <> csid" message). I'm running HEC-RAS version 4.1.0 - my...