Evaluating Slope
Definition: Slope is the steepness of the land expressed as the amount (in percent) of vertical fall per 100 feet of horizontal distance. For example, a 3% slope means a three-foot change in elevation per 100 feet of horizontal distance.
Importance of slope: Slope, along with soil texture (sand, loam, clay) and ground cover, determines how fast water will drain from an area. Water drains quickly from steep slopes; however, erosion may be a problem. Flat surfaces may result in saturated soils. Slope can be managed during road design and layout.
Estimating Slope: Slope can be divided into three broad categories: flat, moderate and steep. Standing downhill and facing uphill, try to look level back into the hill. To help keep your line of sight level, face uphill with your arm stretched out in front of you with a pencil (or a rolled-up dollar bill) pointing up out of your fist. Looking over the tip of the pencil will keep your sight level. Estimate the horizontal, level distance between you and where your line of sight hits the ground. Divide the height distance by horizontal distance to determine the percent of slope. Instruments can be obtained to increase accuracy: an Abney level for $100+, a clinometer for $100 or a slope gauge for $40.
Other sources of slope information:
- USGS topographic maps
- Soil surveys
- Soils maps
On the web:
Google Topographic Maps
USGS Topographic Maps
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| Last Updated: 4/7/2009 12:20:46 PM |
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