Dam Break Model: Starting WSEL Issue

[Hawk]

I have put together a dam break model that utilizes a storage area to represent the dam (essentially the model construction is the storage area, two cross-sections ‘inside’ the dam and which the dam geometry is superimposed on, and 6 downstream cross-sections spaced at ~100′ intervals). I added 500 cfs of baseflow to the inflow hydrograph (represents less than 10% of the peak inflow).

The model is currently stable and running. However, I need to simulate an ’empty’ starting condition within the reservoir. I have set the initial elevation in the reservoir at an elevation which represents 0.5′ of depth (I figured starting with 0′ of depth would create a problem). I also set the two ‘internal’ dam cross-sections to start at this same WSEL (0.5′ of depth).

When I run the model the first time step essentially shows the WSEL within the dam as above the spillway elevation (this represents over 20′ of depth!). So immediately the inflow hydrographs starts spilling over and continuing downstream. This obviously ignores any type of attenuation affect the dam would have.

How can I simulate this ’empty’ starting condition in the reservoir? Is it even possible given the that velocities are practically zero at the two ‘internal’ sections?

Sorry for the lengthy post. Thanks for any help you can provide!

[Chris G.]

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Subject: Re: Dam Break Model: Starting WSEL Issue
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It sounds like you have everything set up except discharge through the dam. Y=
ou can use either gates or pilot flow. If you set your pilot flow equal to y=
our initial flow, your reservoir will stay at whatever elevation you set it a=
t. You are correct to be worried about too low of a depth. 0′ definitely wil=
l crash your model. 0.5′ may be difficult too. Very low depths=3Dunstable mo=
dels.=20
Good luck.=20
Chris

Sent from my iPhone

> On Feb 11, 2014, at 10:32 AM, “Hawk [via HEC-RAS Bloggery Forum]” wrote:
>=20
> I have put together a dam break model that utilizes a storage area to repr=
esent the dam (essentially the model construction is the storage area, two c=
ross-sections ‘inside’ the dam and which the dam geometry is superimposed on=
, and 6 downstream cross-sections spaced at ~100′ intervals). I added 500 c=
fs of baseflow to the inflow hydrograph (represents less than 10% of the pea=
k inflow).=20
>=20
> The model is currently stable and running. However, I need to simulate an ‘=
empty’ starting condition within the reservoir. I have set the initial elev=
ation in the reservoir at an elevation which represents 0.5′ of depth (I fig=
ured starting with 0′ of depth would create a problem). I also set the two ‘=
internal’ dam cross-sections to start at this same WSEL (0.5′ of depth). =20=

>=20
> When I run the model the first time step essentially shows the WSEL within=
the dam as above the spillway elevation (this represents over 20′ of depth!=
). So immediately the inflow hydrographs starts spilling over and continuin=
g downstream. This obviously ignores any type of attenuation affect the dam=
would have. =20
>=20
> How can I simulate this ’empty’ starting condition in the reservoir? Is i=
t even possible given the that velocities are practically zero at the two ‘i=
nternal’ sections?=20
>=20
> Sorry for the lengthy post. Thanks for any help you can provide!=20
>=20
> If you reply to this email, your message will be added to the discussion b=
elow:
> http://hec-ras-bloggery-forum.1091112.n5.nabble.com/Dam-Break-Model-Starti=
ng-WSEL-Issue-tp571.html
> To unsubscribe from HEC-RAS Bloggery Forum, click here.
> NAML

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charset=utf-8
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It sounds like you have everything set up except discharge through the dam. You can use either gates or pilot flow. If you set your pilot flow equal to your initial flow, your reservoir will stay at whatever elevation you set it at. You are correct to be worried about too low of a depth. 0′ definitely will crash your model. 0.5′ may be difficult too. Very low depths=unstable models. 

Good luck. 

Chris

Sent from my iPhone

On Feb 11, 2014, at 10:32 AM, “Hawk [via HEC-RAS Bloggery Forum]” <[email protected]> wrote:

I have put together a dam break model that utilizes a storage area to represent the dam (essentially the model construction is the storage area, two cross-sections ‘inside’ the dam and which the dam geometry is superimposed on, and 6 downstream cross-sections spaced at ~100′ intervals).  I added 500 cfs of baseflow to the inflow hydrograph (represents less than 10% of the peak inflow).

The model is currently stable and running. However, I need to simulate an ’empty’ starting condition within the reservoir.  I have set the initial elevation in the reservoir at an elevation which represents 0.5′ of depth (I figured starting with 0′ of depth would create a problem).  I also set the two ‘internal’ dam cross-sections to start at this same WSEL (0.5′ of depth).  

When I run the model the first time step essentially shows the WSEL within the dam as above the spillway elevation (this represents over 20′ of depth!).  So immediately the inflow hydrographs starts spilling over and continuing downstream.  This obviously ignores any type of attenuation affect the dam would have.  

How can I simulate this ’empty’ starting condition in the reservoir?  Is it even possible given the that velocities are practically zero at the two ‘internal’ sections?

Sorry for the lengthy post.  Thanks for any help you can provide!

---

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

http://hec-ras-bloggery-forum.1091112.n5.nabble.com/Dam-Break-Model-Starting-WSEL-Issue-tp571.html

To unsubscribe from HEC-RAS Bloggery Forum, click here.
NAML

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