Bulletin No. 320 - Soil Erosion in Small Irrigation Furrows

This bulletin reports experimental procedure and data collected in a three-year study of the effect of irrigation furrow slopes and size of streams on the amounts of soil eroded from the furrows. Studies were made in 10 furrows on each of two farm experimental plots, the furrows being in different directions from a central water-stilling basin. The experimental plots were maintained fallow during the season--no crops were grown. Furrow slopes ranged from less than 1 percent to slightly more than 6 percent. Irrigation streams from 5 to 30 gallons per minute at the furrow inlet were measured first by means of triangular weirs and later with circular orifices. Five complete field experimental runs were made on the Forage Experimental Farm soil near Logan, and 6 runs were made on the sandy loam soil of the State Prison Farm about 20 miles south of Salt Lake City. The weight of water-free soil eroded in one hour from 200-foot furrows ranged from only a few pounds in a furrow of less than 1 percent slope to more than 1800 pounds in a furrow of 6 percent slope. Laboratory experiments were made by use of a 32-foot length, 5-channel wooden structure supported on a fulcrum near the middle and on hydraulic jacks at each end to permit adjustment of furrow slopes. Three different soils were used in the laboratory, the Forage Experimental Farm loam, a Box Elder County sandy loam, and the Prison Farm sandy loam. Experiments were made with V-shaped furrows and with flat-bed furrows, using streams ranging from 5 to 15 gallons per minute in each furrow. The slopes of the laboratory furrows ranged from 0.2 percent up to 4.0 percent, and the weights of soil eroded in one hour from one furrow ranged from zero up to 260.8 pounds