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 ft2nd 400 ft 3 ft3rd 400 ft 4 ft4th 400 ft ~ 6 ft5th 400 ft ~ 8 ftRemaining ~ 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 ExpressionNormal Normal Surface – Lake BottomFlood 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?