STORAGE AREAS

[giacomo]

Hello,
I’m quite new in Hecras, even If I studied lots of documents.
Actually I’m trying to do a very simple model, a short river flowing into a storage area in unsteady flow analsys.
My task is to understand how much the water level of the storage area increases during the time of the flood wave to understand if it overflows the dam or not.
In first hypotesis, the model is as simple as I told, later I’ll add a lateral structures and I have to verify the dam breach, but firstI have to fix problems here.

Even if it’s so easy, when I do the simulation, It goes to the end but the resaults are not reasonable.

Just to try to find the problem, I did some try and now my input conditions are:
– upstream bundary condition as flow idrograph in the river of 0.1 m3/s for 2 hours (so very small – actually it’s not a proper river, it’s a channel of derivation from a river so not big)
– initial water level of the storage area at 317 m (I set volume/elevation storage, the dam top is at 318.50 m – just to better understand the volume from 317m to 318.50m is about 90’000 m3)

The program runs, maximum error of 5,2 but it goes to the end but the postprocessor show me that almost immediately the level in storage increases to 318.75 so it overcomes (increasing 1.75 m). But that is not possible, because the volume brought in 2 hours for that flow is 720m3 that is nothing compared to the storage capacity!

I arrived to think that this problem could be due to the difference in hight between the last section upstream the storage (that is higher) and the initial water level in the storage. For example if I set the initial water level in the storage at 318.70 than the process increase it only of few cm!

Or eventually I thought that the program imposes as water level of the storage area the water elevation on the last section upstream (for continuity I think) and beasue this is higher, then the storage seems to be higher, even if the stock volume is risible.

Could I be right? And if so, is it possibile to avoid it? Maybe modifing some bundary conditions or adding a different section usptream the storage? Or using a sort of inline structure?

Actually I need to see the right increase in the storage area.

Thank you veru much for help
Giacomo

[Chris G.]

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Subject: Re: STORAGE AREAS
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Please read this post on The RAS Solution. It should help.=20
http://hecrasmodel.blogspot.com/2010/08/how-to-use-storage-area-to-define.ht=
ml?m=3D1

Chris
Sent from my iPhone

> On Jul 10, 2015, at 4:38 AM, giacomo [via HEC-RAS Help] wrote:
>=20
> Hello,=20
> I’m quite new in Hecras, even If I studied lots of documents.=20
> Actually I’m trying to do a very simple model, a short river flowing into a=
storage area in unsteady flow analsys.=20
> My task is to understand how much the water level of the storage area incr=
eases during the time of the flood wave to understand if it overflows the da=
m or not.=20
> In first hypotesis, the model is as simple as I told, later I’ll add a lat=
eral structures and I have to verify the dam breach, but firstI have to fix p=
roblems here.=20
>=20
> Even if it’s so easy, when I do the simulation, It goes to the end but the=
resaults are not reasonable.=20
>=20
> Just to try to find the problem, I did some try and now my input condition=
s are:=20
> – upstream bundary condition as flow idrograph in the river of 0.1 m3/s fo=
r 2 hours (so very small – actually it’s not a proper river, it’s a channel o=
f derivation from a river so not big)=20
> – initial water level of the storage area at 317 m (I set volume/elevation=
storage, the dam top is at 318.50 m – just to better understand the volume f=
rom 317m to 318.50m is about 90’000 m3)=20
>=20
> The program runs, maximum error of 5,2 but it goes to the end but the post=
processor show me that almost immediately the level in storage increases to 3=
18.75 so it overcomes (increasing 1.75 m). But that is not possible, because=
the volume brought in 2 hours for that flow is 720m3 that is nothing compar=
ed to the storage capacity!=20
>=20
> I arrived to think that this problem could be due to the difference in hig=
ht between the last section upstream the storage (that is higher) and the in=
itial water level in the storage. For example if I set the initial water lev=
el in the storage at 318.70 than the process increase it only of few cm!=20
>=20
> Or eventually I thought that the program imposes as water level of the sto=
rage area the water elevation on the last section upstream (for continuity I=
think) and beasue this is higher, then the storage seems to be higher, even=
if the stock volume is risible.=20
>=20
> Could I be right? And if so, is it possibile to avoid it? Maybe modifing s=
ome bundary conditions or adding a different section usptream the storage? O=
r using a sort of inline structure?=20
>=20
> Actually I need to see the right increase in the storage area.=20
>=20
> Thank you veru much for help=20
> Giacomo=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
> If you reply to this email, your message will be added to the discussion b=
elow:
> http://hec-ras-help.1091112.n5.nabble.com/STORAGE-AREAS-tp1817.html
> To unsubscribe from HEC-RAS Help, click here.
> NAML

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Please read this post on The RAS Solution.  It should help. 
http://hecrasmodel.blogspot.com/2010/08/how-to-use-storage-area-to-define.html?m=1

Chris
Sent from my iPhone

On Jul 10, 2015, at 4:38 AM, giacomo [via HEC-RAS Help] <[email protected]> wrote:

Hello,

I’m quite new in Hecras, even If I studied lots of documents.

Actually I’m trying to do a very simple model, a short river flowing into a storage area in unsteady flow analsys.

My task is to understand how much the water level of the storage area increases during the time of the flood wave to understand if it overflows the dam or not.

In first hypotesis, the model is as simple as I told, later I’ll add a lateral structures and I have to verify the dam breach, but firstI have to fix problems here.

Even if it’s so easy, when I do the simulation, It goes to the end but the resaults are not reasonable.

Just to try to find the problem, I did some try and now my input conditions are:

– upstream bundary condition as flow idrograph in the river of 0.1 m3/s for 2 hours (so very small – actually it’s not a proper river, it’s a channel of derivation from a river so not big)

– initial water level of the storage area at 317 m (I set volume/elevation storage, the dam top is at 318.50 m – just to better understand the volume from 317m to 318.50m is about 90’000 m3)

The program runs, maximum error of 5,2 but it goes to the end but the postprocessor show me that almost immediately the level in storage increases to 318.75 so it overcomes (increasing 1.75 m). But that is not possible, because the volume brought in 2 hours for that flow is 720m3 that is nothing compared to the storage capacity!

I arrived to think that this problem could be due to the difference in hight between the last section upstream the storage (that is higher) and the initial water level in the storage. For example if I set the initial water level in the storage at 318.70 than the process increase it only of few cm!

Or eventually I thought that the program imposes as water level of the storage area the water elevation on the last section upstream (for continuity I think) and beasue this is higher, then the storage seems to be higher, even if the stock volume is risible.

Could I be right? And if so, is it possibile to avoid it? Maybe modifing some bundary conditions or adding a different section usptream the storage? Or using a sort of inline structure?

Actually I need to see the right increase in the storage area.

Thank you veru much for help

Giacomo

---

If you reply to this email, your message will be added to the discussion below:

http://hec-ras-help.1091112.n5.nabble.com/STORAGE-AREAS-tp1817.html

To unsubscribe from HEC-RAS Help, click here.
NAML

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