Developed by T. Endreny at SUNY ESF in the Department of Environmental Resources Engineering
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# Explanation of Measuring River Reach Length & Slope Exercise

### Exercise Objective

To assess how river length and slope for the South Brush River Reach were measured using topographic maps and aerial photos.

### Exercise Explanation

1. ImageJ software was used to view the map provided in this exercise, and then set the 1000 m scale for later measurements of Valley features. The scale is approximately 120 pixels for 1000 meters.
2. Point B, along the downstream section of the South River, below the USGS Gage, is at an Elevation for B of 2450 m, as stated on the map and determined by the thick Elevation contour of 2500 m upstream of Point B.
3. Point A, along the upstream section of the South River, is at an Elevation for A of 2650 m, as determined by counting contour intervals and incrementing 50 m for each interval from Point B.
4. The river length between South Brush River points A and B is about a distance of 5930 m.
5. The river slope is computed as the change in Elevation per change in distance, or (2650 m - 2450 m) / (5930 m - 0 m), for a slope of 0.0337 m/m or 3.37%.

Image courtesy of USGS
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