ent to be absorbed near the discharge point. An easy way to find an appropri- ate delivery rate is to divide the dose volume in gallons per day by the percolation rate in minutes per inch. For example: 150 gpd 30 min per in. = 5 gal per min The total head can be determined as described in Chapter 4 in the section on dosing chambers. With this information, a proper pump can be selected. Furrow irrigation plots are sized exactly as are flood irrigation plots. One difference in design is in the method of distribution of the effluent to the crops. Furrows are dug within the individual plots SO that effluent will flow in them away from the point of input. The furrows in any segment of the plot can be fed simultaneously by a distribution manifold pipe with a large diameter hole (1 in. or so) for each furrow. Again, a flat rock should be placed at each hole to prevent excessive erosion. The furrows should be about 8 to 12 in. below the surfaces of the beds. A slight slope away from the inlets will promote a more even distribution. The beds can be 2 or 3 ft wide. Sprinkle irrigation can be used on medium to coarse textured soils with a percolation rate faster than about 30 min per in. Maximum slope is about 25%. There is no need to divide the irrigated plot into segments. A commercial sprinkler at a pressure of about 5 lb per square inch (11.6 ft) of hydraulic head will cover an area about 20 ft in diameter (Figure 6.14). The best sprinkler to use is the rotating head type with one or two nozzles. The rate of flow should never be lower than 0.25 gal per min, and preferably the pump should be able to deliver 3 to 5 gal per min. If you don't want to use a single sprinkler at the end of a hose, but would rather bury a permanent sprinkler system, the hydraulics become somewhat more difficult. ONSITE WASTEWATER DISPOSAL Figure 6.14 Sprinkle irrigation system. In that case, follow the guidance given for the shallow subsurface distribution system, but install sprinkler heads instead of drilling holes in the laterals. Here is so