Re: [GRASS-user] r.flow: define contributing area

[Rich Shepard]

On Tue, 4 Oct 2016, Rich Shepard wrote:


For current need, it is the opposite of what r.flood

 ^
  Er, make that r.lake instead.

Rich
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Re: [GRASS-user] r.flow: define contributing area

[Rich Shepard]

On Mon, 3 Oct 2016, Thomas Adams wrote:


The only way to -correctly- do this is with hydrodynamic modeling, such as
with HEC-RAS. It can be very crudely approximated with r.damflood (
https://grass.osgeo.org/grass70/manuals/addons/r.damflood.html).


Tom,

  I had tried using HEC-RAS long ago and found it required too much input
data for use with existing environmental data. It's great for research but
not so much in a regulatory context.

  Six years ago this would have been a great module for me to use for a
project had I been aware of it.

  For current need, it is the opposite of what r.flood does and the latter
is the appropriate one for the current purpose.

Thanks for making me aware of this,

Rich
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Re: [GRASS-user] r.flow: define contributing area

[Rich Shepard]

On Tue, 4 Oct 2016, Johannes Radinger wrote:


Maybe have a look at r.lake ... fills the area upstream a dam or a blocked
stream.


Johannes,

  This module looks like it will do the job. The example of flooding along a
small street somewhere in North Carolina is analogous to flooding of
agricultural lands with blocked drainage.

  Yesterday I did not read all of the manual page and missed this.

Thanks very much,

Rich





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Re: [GRASS-user] r.flow: define contributing area

[Rich Shepard]

On Tue, 4 Oct 2016, Johannes Radinger wrote:


Maybe have a look at
r.lake: https://grass.osgeo.org/grass70/manuals/r.lake.html. This module
fills the area upstream a dam or a blocked stream.


Johannes/Thomas,

  I considered r.lake and r.damflood. What I will try to learn from the
manual pages (and references thereon) is whether either of those modules
require the blockage to be on a defined stream/river channel. Some lands can
be on flat land without a stream running through it. These could be a
suburban residential area, industrial/commercial area, or agricultural.
Normally, when precipitation saturates the soils the excess runs off the
surface and has a flow path to prevent flooding. When a drain, culvert, or
swale is blocked the surface water accumulates where it's not wanted.

  This time of year this happens right outside my house where the storm
drain grate in the street just off the curb between me and my neighbor is
covered with dead leaves and the water backs up. Sweeping away the leaves
clears this. But, this is the type of situation for which I need a solution:
where will water back up and flood if drainage from flat land is blocked.

  So, I'll read what I can find about r.lake and r.damflood and see if they
are suitable for this situation.

Thanks both of you,

Rich

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Re: [GRASS-user] r.flow: define contributing area

[Johannes Radinger]

Rich,

Maybe have a look at r.lake: 
https://grass.osgeo.org/grass70/manuals/r.lake.html. This module fills the area 
upstream a dam or a blocked stream.

Cheers,
Johannes



 Original message From: Thomas Adams 
<tea...@gmail.com> Date:04/10/2016  04:32  (GMT+01:00) 
To: Rich Shepard <rshep...@appl-ecosys.com> Cc: 
grass-user@lists.osgeo.org Subject: Re: [GRASS-user] r.flow: define 
contributing area 
Rich,

The only way to -correctly- do this is with hydrodynamic modeling, such as with 
HEC-RAS. It can be very crudely approximated with r.damflood 
(https://grass.osgeo.org/grass70/manuals/addons/r.damflood.html).

Tom

On Mon, Oct 3, 2016 at 7:39 PM, Rich Shepard <rshep...@appl-ecosys.com> wrote:
  Reading the r.flow manual page suggests that the use of the '-u'
(upstream) option allows determination of flowlines and lengths that can be
used to delineate the area that would drain to a specific point. Is this
correct?

  To determine the area flooded if an outlet is plugged would require the
inverse of r.drain. That module calculates the area flooded with surface
water originating from a specific point; e.g., a hole in a dike or dam. The
closest I've seen to do the opposite seems to be r.flow. The quantity of
surface water and the rate of accumulation and infiltration into the vadoz
zone are not of interest, only the area flooded is needed.

  The modules listed under the Natural Hazards application page all appear
to delineate the area flooded from a point source. Can any of these be used
backwards to delineate the area flooded if an outlet is blocked?

  I'd appreciate pointers and suggestions based on cumulative experience
here for appropriate module(s).

TIA,

Rich
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Re: [GRASS-user] r.flow: define contributing area

[Thomas Adams]

Rich,

The only way to -correctly- do this is with hydrodynamic modeling, such as
with HEC-RAS. It can be very crudely approximated with r.damflood (
https://grass.osgeo.org/grass70/manuals/addons/r.damflood.html).

Tom

On Mon, Oct 3, 2016 at 7:39 PM, Rich Shepard 
wrote:

>   Reading the r.flow manual page suggests that the use of the '-u'
> (upstream) option allows determination of flowlines and lengths that can be
> used to delineate the area that would drain to a specific point. Is this
> correct?
>
>   To determine the area flooded if an outlet is plugged would require the
> inverse of r.drain. That module calculates the area flooded with surface
> water originating from a specific point; e.g., a hole in a dike or dam. The
> closest I've seen to do the opposite seems to be r.flow. The quantity of
> surface water and the rate of accumulation and infiltration into the vadoz
> zone are not of interest, only the area flooded is needed.
>
>   The modules listed under the Natural Hazards application page all appear
> to delineate the area flooded from a point source. Can any of these be used
> backwards to delineate the area flooded if an outlet is blocked?
>
>   I'd appreciate pointers and suggestions based on cumulative experience
> here for appropriate module(s).
>
> TIA,
>
> Rich
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