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I reviewed your PDF diagram and StormNET model file. The model appears to be handling the setup as you described.

The only concern I have about your model is that you are using the Rational Method for your runoff computations, and this method is really inadequate to check the detention pond size since it does not include the storm duration in its computations. I recommend either switching to the Modified Rational Method or one of the other event-based hydrology methods (i.e., TR-55, TR-20, EPA SWMM, HEC-1, etc.).]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16210.html Mon, 05 Jan 2009 12:43:48 -0700 Summary Err, Warn, Notes. Looking at the finished computations window it says: " **** Matrix Solution Failed **** Minimum error exceeds allowable tolerance at 01JAN2008 1200 River upper 154.* Finished Unsteady Flow Simulation" Is the hydrograph output the same as the view profiles button? That shows the EG line reaching 3,000,000 m over one XS (terrain El. is 2500 m and under). That suggests a problem (!) I'll try putting in more XS. The terrain is mountainous so relief does change between them. Thanks for the reply! Neil]]>
Those error messages are what I see when running unsteady calc (icon of guy running over hill), it fails, and I click on View > Summary Err, Warn, Notes.

Looking at the finished computations window it says:


" **** Matrix Solution Failed ****

Minimum error exceeds allowable tolerance at 01JAN2008 1200

River upper 154.*


Finished Unsteady Flow Simulation"

Is the hydrograph output the same as the view profiles button? That shows the EG line reaching 3,000,000 m over one XS (terrain El. is 2500 m and under). That suggests a problem (!)

I'll try putting in more XS. The terrain is mountainous so relief does change between them.


Thanks for the reply!

Neil]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16219.html Mon, 05 Jan 2009 11:08:25 -0700
SITUATION1: Based upon the attached info, do you think that I am adequately modeling for the backwater effect from the overloaded stormdrain? (Note, I rely on the volume calculation of excess water out of the junction, not elevation because ponding in my parking lot is irregularly shaped)

SITUATION2: Basically, instead of letting water back into the parking lot, if I wanted to divert excess backwater above a certain elevation via overland flow path, where could I fit a diverter into this scheme?

Thanks
Jesse]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16210.html Mon, 05 Jan 2009 10:17:22 -0700
"Warning: The velocity head has changed by more than 0.5 ft (0.15 m). This may indicate the need for additional cross sections.
Warning: The energy loss was greater than 1.0 ft (0.3 m). between the current and previous cross section. This may indicate the need for additional cross sections."

This is a steady flow computation warning. After performing the unsteady computations, RAS will perform a post process [steady flow] analysis on select profiles for more detailed output. So if this is what is going on: if the unsteady flow run goes unstable, the post process [steady] results are meaningless and the steady flow errors should be ignored.

If the unsteady flow model is unstable, you might try a shorter time step and examine the hydrograph output to try and determine why/where the unsteady is going unstable.

2km intervals may or may not be sufficient. If the cross sections are large and/or the cross sections do not change radically from one to the next, 2km may be more than sufficient (sounds like it probably is). If there are large changes in area, than 2km may be too far apart regardless of the ground slope.]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16219.html Mon, 05 Jan 2009 06:57:11 -0700
[url=http://www.hec.usace.army.mil/software/hec-ras/hecras-document.html]HEC-RAS Documentation[/url]

and download:

HEC-RAS 4.0 Applications Guide

This contains a bunch of example applications and a step-by-step tuturial on entering data.

Also, if you haven't already, install the example projects and look at them.]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16215.html Mon, 05 Jan 2009 06:46:18 -0700
I'm trying to get working an unsteady simulation model of a 130 km river reach that drops about 900 m. The flow data is given in daily intervals for 100 days and intially set the computation interval as 1 day.

At the moment it goes unstable within a few days of simulation-time. I have tried reducing the computation interval to no avail. The error log has lots of warnings such as:

"Warning: The velocity head has changed by more than 0.5 ft (0.15 m). This may indicate the need for additional cross sections.
Warning: The energy loss was greater than 1.0 ft (0.3 m). between the current and previous cross section. This may indicate the need for additional cross sections."

How seriously should take these error messages? I've got XS at 2 km intervals, meaning that the overall gradient between XS is 0.007. If I were to put in enough cross sections so that the energy loss between them is less than 0.3 m I would need on average one every 42 m! Is this really necessary? Or is there something else I should be checking?

Thanks,

Matty]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16219.html Sun, 04 Jan 2009 11:22:30 -0700
A quick summary of the WSEL calculation for a steady flow simulation is this:

1) Start with a known water surface elevation at a cross section. This WSEL is from your boundary condition.

2) Assume a WSEL at the next upstream cross section (assuming a subcritical analysis).

3) Calculate conveyance and the velocity head. The conveyance calculation takes into account the wetted perimeter that you originally asked about.

4) With the conveyance calculation, determine the average friction slope.

5) With the results of the two previous steps, calculate the energy head loss between the two cross sections (equation 2-2 in the manual).

6) Then solve for the WSEL using the energy equation (equation 2-1 in the manual).

7) Compare the calculated WSEL with the assumed WSEL and if necessary repeat the calculation until the assumed and calculated WSEL match within your specified tolerance.]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16216.html Fri, 02 Jan 2009 05:01:59 -0700 I tried to do a water quality model and my problem arose when editing meteorological conditions. I think that this part of the program is still unestable.
Best regards.
Javier]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16209.html Thu, 01 Jan 2009 04:33:34 -0700
I have a check by myself and know that R = A/P. It is fine.

But the next question is how HEC-RAS calculate the water surface elevation.

Best regards,

Tri Van]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16216.html Wed, 31 Dec 2008 07:44:12 -0700
As I know they have new version of Checkras which is compatible with HEC-RAS 4.0

Best regards,]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16212.html Wed, 31 Dec 2008 06:09:54 -0700
Can anybody let me know how HEC-RAS calculate the hydraulic radius?

It is clear that the calculated Hydraulic Radius (R) (from HEC-RAS) plus the lowest point (LP) of a cross-section does not equal to the water surface elevation. In addition, the difference between the the water surface elevation and the combination of R+LP change according to the hydraulic roughness applied at a cross-section.

Could any body explain more how HEC-RAS do the calculation?

Many thanks and happy new year.

Best regards,

Tri Van]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16216.html Wed, 31 Dec 2008 06:07:22 -0700
Thank You.]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16215.html Tue, 30 Dec 2008 18:11:03 -0700 http://www.bossintl.com/forums/showthread/s/1/threadid/15652.html Tue, 30 Dec 2008 08:01:20 -0700 http://www.bossintl.com/forums/showthread/s/1/threadid/16214.html Tue, 30 Dec 2008 07:18:47 -0700 = 2.80 THEN PUMP Pump-2.2 STATUS = ON RULE PS2_P2.2.2 IF NODE Pond-2 INFLOW >= 1.5 THEN PUMP Pump-2.2 STATUS = ON RULE PS2_P2.2.3 IF NODE Pond-2 DEPTH <= 1.6 THEN PUMP Pump-2.2 STATUS = OFF [/QUOTE] the DEPTH condition is working properly both for the switch ON & OFF... (note that the Pond-2 element is a detention pond and NOT a junction... but i take it this is not a problem) what does not work properly is the INFLOW condition. what am i doing wrong? the units in the conditions are the same as all the rest volumetric units in the project. right? (in my case cms) note that: the last parts (pipes) of the drainage network is always filled with water and i figured, there is a chance that the water does not 'flow' as fast when the pipes are filled. but i checked the time series plot of the 'total inflow' to the pond and it seems that (after the initial transients) there is an steady state inflow to the pond of 1.35cms.... so i reduced the critical inflow value to 0.5. and removed the DEPTH condition of the specific pump (i commented out RULE PS2_P2.2.1 using ';' as a comment separator)... now the pump does not switch ON anymore... any clues? thank you in advance for your help nass]]> i am trying to get some rules for pumps to work on a drainage model i'm working on.

the topology is: 3 separate parts of a drainage network are connected to a detention pond. the pond is a storage tank and there are 3 identical pumps that pump water out of the tank and to a higher level...

The pump network is controlled by a microprocessor that uses as inputs the water level (DEPTH) in the tank, but also the INFLOW of water to tank...

using control rules i checked the manual and used the following conditions for the switch ON (these are the rules for pump 2. pumps 1 & 3 are identical)

[QUOTE]RULE PS2_P2.2.1
IF NODE Pond-2 DEPTH >= 2.80
THEN PUMP Pump-2.2 STATUS = ON

RULE PS2_P2.2.2
IF NODE Pond-2 INFLOW >= 1.5
THEN PUMP Pump-2.2 STATUS = ON

RULE PS2_P2.2.3
IF NODE Pond-2 DEPTH <= 1.6
THEN PUMP Pump-2.2 STATUS = OFF
[/QUOTE]

the DEPTH condition is working properly both for the switch ON & OFF... (note that the Pond-2 element is a detention pond and NOT a junction... but i take it this is not a problem)

what does not work properly is the INFLOW condition. what am i doing wrong? the units in the conditions are the same as all the rest volumetric units in the project. right? (in my case cms)

note that:
the last parts (pipes) of the drainage network is always filled with water and i figured, there is a chance that the water does not 'flow' as fast when the pipes are filled. but i checked the time series plot of the 'total inflow' to the pond and it seems that (after the initial transients) there is an steady state inflow to the pond of 1.35cms....

so i reduced the critical inflow value to 0.5. and removed the DEPTH condition of the specific pump (i commented out RULE PS2_P2.2.1 using ';' as a comment separator)... now the pump does not switch ON anymore...

any clues?

thank you in advance for your help
nass]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16214.html Tue, 30 Dec 2008 00:34:53 -0700
I'm trying to set up a distributed model in HEC-HMS for a catchment area in Greece, aiming to couple it with gridded precipitation from numerical weather forecast models. While trying to set up the ModClark files in GeoHMS I can see it only supports the HRAP and SHG projections (not applicable in Europe).

I'd be grateful if you could provide some feedback on how to use different projections in GeoHMS. Unless HEC-HMS can't be used for distributed modelling outside the US. One last thing: any alternative to ascii2grid for ascii import to DSS?

Thank you in advance.

Zisis]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16213.html Mon, 29 Dec 2008 23:13:11 -0700
Has anyone else encountered this?

Has anyone else overcome this?

Thanks.]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16212.html Mon, 29 Dec 2008 12:29:49 -0700
Make certain you are using the EPA SWMM hydrology method, and then in the Subbasins dialog, select the Flow Properties tab. There is an entry labeled "Groundwater Aquifer". Click on the [...] browse button to display the Groundwater Aquifer Assignment dialog to attach a groundwater aquifer to subbasin.]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16211.html Mon, 29 Dec 2008 09:20:33 -0700 http://www.bossintl.com/forums/showthread/s/1/threadid/16211.html Mon, 29 Dec 2008 08:40:16 -0700
Note, however, that you will want to run your model using the hydrodynamic routing method. As such, you do not want to use a flow diversion structure, since it will be converted to a junction when operating the hydrodynamic routing method. However, to model the overflow, simply connect the weir structure to the appropriate storage element. (This is were it got a little confusing in your description.) If the overflow is from the detention pond, then connect the weir to this element. If the overflow is from the storm drain junction box, then connect the weir to this element.

If you continue to have questions, please provide me with a sketch of what you are trying to represent and your StormNET model file.]]> http://www.bossintl.com/forums/showthread/s/1/threadid/16210.html Fri, 26 Dec 2008 07:50:24 -0700