Steps for Modeling a Proposed New Reservoir in GIS Requirements: ArcGIS ArcMap, ArcScene, Spatial Analyst, and 3D Analyst There s a new reservoir proposed for Right Hand Fork in Logan Canyon. I wanted to estimate the footprint of the proposed reservoir and create a model that I could use to generate the elevation-storage and elevation-surface area relationships for the proposed reservoir. I also wanted to use the outline of the proposed reservoir to overlay with other datasets (e.g., roads and land cover) to see what the impact would be. The following are the steps I followed: 1. Download 10-m DEM from the MRLC website 2. Project the DEM into NAD83 UTM Zone 12N (ned10) 3. Create a polygon clip area feature class (clipsquare) to clip the larger DEM to a smaller area (I don t want to have to process the whole thing) 4. Clip DEM to a smaller area just to speed analysis (ned10sub this dataset is the basis for my analysis) 5. Convert clipped DEM to a TIN using 3D Analyst Tools à Conversion à Raster to Tin allowing 0.5 m elevation difference (elevationtin) 1
6. Create a Dam surface tin. a. Create a new line feature class (damlines). Start editing and add a line representing the alignment of the dam, but extending far beyond the dam edges. Use the copy parallel function of the editor toolbar dropdown to copy the line to the right 10 m (this creates a new line to represent the dam crest width of 10 m). Then use the copy parallel function to copy a line to the right 310 m to represent the slope of the dam face + the crest. This new line is the heal of the dam. Copy parallel to the left 300 m to represent the downstream face of the dam this is the toe of the dam. 2
b. Create a new column in the attribute table for the damlines feature class called Elevation as a double. Assign elevation values to each of the lines. The two crest lines were set to 1920 m. This is a total WAG based on the surrounding elevations. I don t know what the actual dam alignment or height would be. The upstream and downstream line elevations were set assuming a slope of 2:1 for the dam faces (1770 m for each). This extends below the earth surface, but that s what I want. c. Now convert these lines to a tin using 3D Anayst Tools à Data Management à TIN à Create TIN. Call the output damtin. 3
The Dam Surface Tin in ArcMap: 4
The Dam Surface Tin as shown in ArcScene: The Dam Surface Tin as shown in ArcScene with the DEM Tin: 7. Now create the outline contour of the potential reservoir from the elevation tin. It will never happen that the reservoir will get as high as the crest of the dam, but for the purposes of 5
creating the full elevation-volume, elevation-surface area curve, create this contour at the crest elevation of the dam (I set it at 1920 m). a. Create a flat tin surface at 1920 m elevation. i. Digitize a few parallel lines covering the whole area in a new feature class (surface1920lines). The first line should align with the upstream crest line of the dam. Use the copy parallel function in the editor toolbar to create the additional lines. ii. Create an Elevation attribute column as a double in the table for this feature class and assign an elevation for each line of 1920 m using the field calculator. iii. Convert the surface1920lines feature class to a flat tin surface (surface1920tin) using 3D Anayst Tools à Data Management à TIN à Create TIN 6
b. Now subtract the elevationtin from the surface1920tin produced in the last step to get a polygon representing the contour at 1920 m (polygon1920). Use 3D Analyst Tools à Triangulated Surface à Surface Difference 7
The DAM and the 1920 m surface in ArcScene: The DAM, 1920 m Surface and DEM Tin in ArcScene: 8
c. Now edit the resulting polygon1920 feature class to delete everything but the 1920 m elevation polygon representing the reservoir. 9
8. Now create the polygon footprint of the Dam (dampolygon). a. Use 3D Analyst Tools à Triangulated Surface à Surface Difference to subtract the elevationtin from the damtin. The following is the result: b. Edit the Dam polygon feature class to include only the dam footprint. 10
9. Now, we need a tin of just the reservoir for volume and surface area creation that includes everything below 1920 m elevation, but that also includes the slope of the upstream face of the dam. So do the following: a. Convert the polygon1920 feature class to a raster (reservoirrast) with value of 1 inside of the polygon and nodata outside using Conversion Tools à To Raster à Polygon to Raster. Set the environment settings so extent, grid sell size, and snap raster are the same as the input DEM (ned10sub) before doing this. 11
b. Now multiply the reservoirrast by the input DEM (ned10sub) to get a raster of the elevation for grid cells within the 1920m contour (reservoirelevations) using raster calculator. 12
c. Now convert the new raster of elevation values within the reservoir (reservoirelevations) to points using Conversion Tools à From Raster à Raster to Point (reservoirpointelevations) d. These points all have the right elevations except the ones that are on top of the new dam footprint (dampolygon) because they are based on the original DEM. So, use select by location to extract all points that do not intersect the new dam footprint and save to a new feature class (reservoirpointelevationsnodam) 13
e. Use select by location to select the points from reservoirpointelevations that intersect the dam footprint and convert to a new feature class (dampoints). f. Now the elevation values in the dampoints feature class are wrong because they are based on the ground elevation. So, I need to use the 3D Analyst Tools à Functional Surface à Interpolate Shape function to set the elevation values in the dampoints to 14
the elevations of the damtin surface. This function creates a new feature class (dampointelevations). 10. Now I can finally create a tin surface for the whole reservoir (reservoirtin) from the dampointelevations and the containpointelevationsnodam point feature classes using 3D Analyst Tools à Data Management à TIN à Create Tin. 15
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