Is this possible with HEC-RAS?
Is this possible with HEC-RAS?
(OP)
Hi.. Everyone,
I'm little new to the HEC-RAS and have following question,
Two streams connect together and forming one stream. Those two streams starting from two inland water bodies and final stream goes to sea. I know all the cross sections of all streams and starting and ending water surface elevations. I know manings n values, expansion and contraction co-efficients. What I don't know is, flows of each of these streams. I don't know any hydrographs either. My problem is to find the "FLOWS IN EACH OF THESE STREAMS"
Is this possible with HEC-RAS? If so can you please anyone explain me How can I do this?
I'm little new to the HEC-RAS and have following question,
Two streams connect together and forming one stream. Those two streams starting from two inland water bodies and final stream goes to sea. I know all the cross sections of all streams and starting and ending water surface elevations. I know manings n values, expansion and contraction co-efficients. What I don't know is, flows of each of these streams. I don't know any hydrographs either. My problem is to find the "FLOWS IN EACH OF THESE STREAMS"
Is this possible with HEC-RAS? If so can you please anyone explain me How can I do this?





RE: Is this possible with HEC-RAS?
Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve
RE: Is this possible with HEC-RAS?
I'm still learning this HEC-RAS package, I'm little confused with the capabilities of this software although i refered there User manual and Hydrolic reference. What are the things actualy we can do with this? and, if you know please mention what are the other software currently available, which are best for this kind of job?
RE: Is this possible with HEC-RAS?
Others include HEC-HMS, SMADA, and many commercial,and expensive, programs. Those I've listed are the least expensive and most available. If you have Google, or any decent search engine, search for them. If you don't have a good seach engine, get one ! It will save you thousands of dollars in money wasted on programs that promise more than they can possibly deliver.
Google, by the way, is also FREE.
good luck
RE: Is this possible with HEC-RAS?
Can anyone please give me the capabilities of HEC-RAS. I'm little confused with the capabilities of this software What are the things actualy we can do with this?
RE: Is this possible with HEC-RAS?
I read the Hydraulic Reference Manual and had no trouble understanding the software. I've used it for five 100-year flood elevation studies over the past year.
RE: Is this possible with HEC-RAS?
RE: Is this possible with HEC-RAS?
I have a topo that extends 500' left and right of the centerline of a creek. Is it accurate to import a USGS map and add the highest point with that elevation from the USGS map on to the cross-section for HEC-RAS. In other words, if the elevation from the sides of the creek keeps increasing until a distance of 5280 then it starts to drop. If you do not do this then HEC-RAS extends a vertical lines and analyzes based on the info you give it. Which is more accurate?
RE: Is this possible with HEC-RAS?
First, I'd suggest you start a new thread. You're much more likely to get an answer that way.
It is usually OK to extend your cross sections laterally but it depends on the range in elevation of the calculated water surface. If the flooded area is very wide, then you may want to consider field surveying the whole flood plain. But, if the flood plain is narrower than 1000' ( 500' on each side of the creek ) then the ground surface outside that doesn't matter since it is not "Wetted" by the flood flow.
Also look at the contour interval of the USGS map. Remember that the probable error in elevation at any point is equal to one half the contour interval. If you have 40' contours, your probable error at any point is plus or minus 20'.
By all means, visit the site and make a judgement about where you need additional topography and where a simple extrapolation would be good enough.
good luck
RE: Is this possible with HEC-RAS?
Neither option sounds particularly accurate, but it could just be the way you described it not being clear to me.
What are you using the HEC-RAS model for? Can you justify limited accuracy? How long would it take you to correctly enter the cross-sections? Is this extra time worth the accuracy? Is a USGS topographical map the best you can do?
I built some HEC-RAS models based on surveys of the main channel merged with a County Planning Commission-owned DTM created off aerial photographs to an accuracy of 5'. We were defining a 100-year flood zone adjacent to a residential subdivision. Acknowledging the inaccuracy inherant in the model, we allowed an additional 2' in setting the finished floor elevations.
By all means import your USGS topo, but remember that its accuracy is limited to the contour interval reflected on the map. Don't just add the highest point, add points at every change in slope, in order to correctly model the flow area. You'll need to specify roughness coefficients on the overbanks, and I'd wager that these will change horizontally along your cross-sections. You'll need to add a point where your manning's coefficient changes, too.
Good luck.