I want to ensure my understanding how to use r.lake for my need.
It would be good to produce animation of flooded area with increasing
precipitation; use of the '-o' option is required. But, perhaps I need to
produce a large series of individual maps.
Under what condition is use of the '-n' option appropriate?
If I want a final water_level of 1 m above the elevation of the specified
coordinates in increments of 0.254 mm how can I specify this for the
animation? The manual's description tells me that the 1 m water_level is the
final height and the elevation of the specified coordinates is the starting
height. How are map-to-map increments specified? A related question is
whether the water level associated with a given map can be produced. That
is, can individual maps in the animation be related to specific water
levels? This quantification of output map and water level above the starting
elevation is very important.
All thoughts, suggestions, and pointers to more information are welcome.
Rich
Rich,
You understand, don’t you, that the point you are using to define your ‘dam’, delineates a watershed; so, there is runoff from the watershed, which will not be uniform in its contribution – a fundamental issue in hydrology, which is more critical to quantify accurately at smaller spatial scales – knowing the rainfall rate alone will not give you what you need. You also need to generate a storage-elevation curve, which will relate the water level (which r.lake needs) to the volume behind your dam (assuming none escapes, otherwise the problem gets more complicated) – the change in volume depends on the inflow rate, which a hydrologic model will provide. Typically, hydrologic models are calibrated against observed flow data. There is the further assumption that the inflow spreads over the lake surface instantaneously, which for a small surface area is not altogether unreasonable…
Tom
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On Wed, Oct 5, 2016 at 11:48 AM, Rich Shepard <rshepard@appl-ecosys.com> wrote:
I want to ensure my understanding how to use r.lake for my need.
It would be good to produce animation of flooded area with increasing
precipitation; use of the ‘-o’ option is required. But, perhaps I need to
produce a large series of individual maps.
Under what condition is use of the ‘-n’ option appropriate?
If I want a final water_level of 1 m above the elevation of the specified
coordinates in increments of 0.254 mm how can I specify this for the
animation? The manual’s description tells me that the 1 m water_level is the
final height and the elevation of the specified coordinates is the starting
height. How are map-to-map increments specified? A related question is
whether the water level associated with a given map can be produced. That
is, can individual maps in the animation be related to specific water
levels? This quantification of output map and water level above the starting
elevation is very important.
All thoughts, suggestions, and pointers to more information are welcome.
Rich
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On Wed, 5 Oct 2016, Thomas Adams wrote:
You understand, don't you, that the point you are using to define your
'dam', delineates a watershed;
Tom,
Yes, I do understand.
You also need to generate a storage-elevation curve, which will relate the
water level (which r.lake needs) to the volume behind your dam (assuming
none escapes, otherwise the problem gets more complicated) -- the change in
volume depends on the inflow rate, which a hydrologic model will provide.
This is flat, agricultural land with no defined streams. The only inflow
comes from precipitation; what does not infiltrate into the soil and drains
to the swale adjacent to the county road, along with surface runoff, flows
through a culvert (the 'dam.')
Typically, hydrologic models are calibrated against observed flow data.
There is the further assumption that the inflow spreads over the lake
surface instantaneously, which for a small surface area is not altogether
unreasonable...
My reading of the manual pages for r.sim.water and Itzi suggest they, too,
require perennial streams in defined channels. There should be a set of
modules that work for my need here. If you have suggestions please share
them with me.
Thanks,
Rich
On Wed, 5 Oct 2016, Rich Shepard wrote:
This is flat, agricultural land with no defined streams. The only inflow
comes from precipitation; what does not infiltrate into the soil and
drains to the swale adjacent to the county road, along with surface
runoff, flows through a culvert (the 'dam.')
Let me refine my answer; perhaps that will help. Given a LiDAR DEM and
coordinates for a point on the map, what modules will predict (and display
on an output map) the area flooded for a given height of standing water with
higher elevations that that point?
Rich
On Wed, 5 Oct 2016, Rich Shepard wrote:
Let me refine my answer; perhaps that will help. Given a LiDAR DEM and
coordinates for a point on the map, what modules will predict (and display
on an output map) the area flooded for a given height of standing water
with higher elevations that that point?
There's a simple solution to this: using r.contour I created a contour map
of the area. I can mark the 'dam' elevation and calculate areas of higher
elevation. That should suit the purpose.
Without a perenial stream, or even stream channels, normal hydrological
models have nothing with which to work. So, the above solution is the most
parsimonious one.
Thanks, all,
Rich