Dear Patrick Delaney,


Thanks very much for your help and adivce. I have tried to send an E-mail to DHI
for technical help. Whereas, I haven't any reply from them yet.

Time step of MIKE11 is 5 min, while that of overland flow is 1 hour. To increase
the stability as you suggested, I increase the delta value in MIKE11 HD
parameters to 0.7. Warnings 3 and 4 still exist, but the reduction percentage is
largely decrease, which may be a piece of good news.

As for the evaporation redcution from pond water in warning 3, errors were
focused on 4 grid cells only. All of them are not sinks. I am confused about the
UZ classification mentioned in the warning. What requirement it should meet
with?

In addition, I am encountered other problems. For instance, simulated depth of
phreatic surface is positive value in some part of the catchment and the
simulated discharge is extremely large.

I would like to despcribe a bit about some settings of my model.

1/ MIKESHE resolution: 50*50 m

2/ MIKE11 river branch: kinematic rounting using Muskingum_Cunge routing. No
loop part is included. By the way, this rounting method is not suitable for loop
parts?

3/ Cross-section is set for almost every river point. Distance between 2 points
are around 50 - 100 m. River bank elevation is equal to that on the
corresponding MIKAESHE grid. Depth of the channel ranges from 1 m to 1.4 m,
while the width ranges from 3 m to 4.5 m.

4/ As for groundwater, lower level of aquifer in UZ zone is -15 m relative to
ground and the intial potential head for computational aquifer is -2 m relative
to ground.



Thanks a lot again,
Stephy




--- In hydrologymodel@..., Patrick Delaney <patrickgdelaney@...>
wrote:
>
> Hello Stephy,
>
> The warnings you are seeing are fairly well explained, but if you are
uncertain, it's always a good idea to contact DHI Technical Support for
assistance on these issues. Without seeing your actual model, it is difficult
to offer up anything more than anecdotal suggestions, but here goes:
>
> 1/ It is difficult to determine what the problem is without knowledge of the
river cross-section geometry and topography of the adjacent land surface, but
judging from the error, it seems to be a numerical instability issue and I would
try reducing the MIKE 11 time step.
>
> 2/ no idea
>
> 3/ This one is pretty self-explanatory and can likely be addressed by reducing
your overland flow time step.
>
> 4/ Again, reduce the MIKE 11 time step.
>
> 5/ This one might be helped by reducing time steps as well, but I am not as
confident about this one.
>
> In general, the MIKE 11 1D river flow model should have time steps ranging
from 1-15 minutes depending on a wide range of factors. If it's a deep slow
moving river, then you can probably get away with larger time steps, but that
doesn't seem to be the case with your model.
>
> Hope this helps.
>
> Patrick Delaney
>
>
>
> To: hydrologymodel@...
> From: stephychanym@...
> Date: Sat, 8 Aug 2009 08:06:52 +0000
> Subject: [hydrologymodel] Warnings related to MIKESHE coupling with MIKE11
>
> Dear friends,
>
> I got warnings as follows when using MIKESHE coupling with MIKE 11 to simulate
stream discharge of a small catchment. How I could find out the problems and
solve them? Thanks a lot.
>
> 1/ Warning no 42: The lateral outflow in BRANCH173 at chainage 613.646 was
> greater than the amount of water available.
> The lateral outflow has been modified to avoid the local water
> level falling below the bed level. This modification has occured 9506 times.
> First time at time step 145.
>
> 2/ Warning No 53: The total corrected volume is 0.000 m3.
>
> 3/ WARNING: Evaporation from ponded water on ground surface has been reduced
> in UZ class(es) with less ponded water in transfer point(s)
> than in the corresponding computational point(s).
> Total apriori : 171.4545 [ catchment mm ]
> Total used : 23.13893 [ - - ] ( 13.50 % of apriori ).
> Please check the applied UZ classification.
>
> 4/ WARNING: Exchange flows FROM RIVER TO SZ reduced to avoid drying river.
> No. of time steps: 63510
> Total outflow before reduction: 19147.67 m3
> Total reduced outflow : 7581.811 m3 ( 39.59652 %)
>
> 5/ WARNING: Retention curve too steep. Processed water contents
> and/or capacities have been adjusted.
> - average reduction of Theta = -2.4895095E-03
> Max = -4.3501346E-03 from 1.0971338E-02 to 6.6212039E-03 at pF =6.950000
> - average rel. change of capacity = 9.9819386E-04
> Max = 3.3869114E-02 from 4.8696500E-09 to 5.0345808E-09 at pF =6.950000
>
> (The soil I use in my study is decomposed grantie soil with the hydraulic
conductivity of 1.1E-005 m/s. no specific value for other parameters )
>
> Thanks very much for your kind help!
>