Date post: | 18-Jan-2016 |
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Lake Volumetrics
Introduction
DEM from USGS◦ Digitized version of 1:24,000 topo quadrangle◦ Vertical accuracy 5m, 30m resolution
KML files, digitized from Google Earth◦ Lake perimeter◦ Drain line for dam
Drain depth estimations in 400ft increments
BING aerial imagery
Methods: Data
Drain Line
Depth
1st 400 ft ~ 1 ft
2nd 400 ft 3 ft
3rd 400 ft 4 ft
4th 400 ft ~ 6 ft
5th 400 ft ~ 8 ft
Remaining ~ 10 ft
Lake perimeter and drain line depths (m)
Methods Overview
• Edit DEM bottom topography• Translate depth to elevation
Create DEM of Lake Bottom
• Edit DEM 2 surfaces • Identify elevation of 2 surfaces
Create DEM of Lake Surface
(normal/ flood)
• Raster subtraction = depth values• Volume Estimations in Excel
Generate Depth Raster, Volume
Estimations
Convert 30m raster DEM to center points Edit points within the lake perimeter to
reflect drain depth estimations
Create DEM of Lake Bottom
Center-point values edited to reflect the lake bottom. Values are based on drain line depth
estimations.
Points file mass points for terrain creation Interpolate terrain to raster DEM with cell
size 6.35m*
Lake Bottom DEM Cont’d
Kml shoreline doesn’t make ‘elevational’ sense...
Modified using aerial imagery, DEM Flood level established from photos taken in
Summer 2011...
Establish shoreline
Select all points within lake perimeter at each height
Assign new value to selected points
Create terrain from points and interpolate to raster
Create DEM of Lake Surface
Condition
Elevation
Flooded 39.14m
Normal 38.2 m
Raster subtraction using Lake bottom DEM and Lake surface DEMs
Depth Raster
Depth Expression
Normal Normal Surface – Lake Bottom
Flood Flood Surface – Lake Bottom
Normal Height Flood Height
Performed in Excel Normal and flood depth rasters converted to
ascii and imported to Excel Volume: Cell Length x Width x Height
(depth)◦ 6.35m x 6.35m x (depth)
Sum all volume calculations
Analysis: Volume
Normal Water Level: 85,569.16 m3 (112,095.6
yd3)
Flood Water Level: 190,154.91 m3
(249,102.93 yd3)
Data: ◦ 30m DEM from topo contour digitization/
interpolation poor quality for scale of analysis◦ Lake depths estimations from lake users
Terrain to Raster◦ Raster grid size (6.35m): questionable
Should match input size (30m), but too coarse for lake perimeter—excludes large amounts of lake area
ESRI default: based on the overall dimensions of the minimum bounding rectangle and the number of input elevation points
Discussion
Questions?