Tham khảo tài liệu 'water conservation part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 6 Water Conservation Design criteria used when installing the water ponding dikes at the Jornada are specified by Tromble 1983 . These criteria varied because of the characteristics of the individual site. Dikes were installed on fine to medium textured soils where the soil sealed rapidly during rainfall events thereby producing surface runoff. Furthermore the dikes were placed in areas of wasteland supporting little or no vegetation similar to the scalds in Australia . Dikes were placed starting at the highest place on the slope and working downslope. The direction of water flow from one dike to the next was regulated by locating one end of the dike higher than the other end so that water flowed out the lower end of the dike once it filled Tromble 1983 . The distance between dikes was a function of the slope and expected water ponding depth. Enough distance was left between dikes to provide a source area for surface runoff water. Usually a 1 1 or 2 1 ratio of water runoff area to ponding area is satisfactory on a scald area Tromble 1983 but other authors cite values of 5 1 to 25 1 depending upon local conditions Vallentine 1989 . Compared to the shallow water ponding dikes much deeper ponds or lakes are also necessary in rangelands for watering livestock as well as for providing fringe benefits to wildlife. Placement of these water sources depends not only upon water availability but also on animal numbers available forage soil properties and abiotic factors. Many approaches to providing water have been tested on rangelands. The two most usual developed water sources are from drilled deep water wells and earthen dams that cause the formation of stock ponds. Early in the 20th century it was recognized that competition to use reliable well water would become intense and that earthen dams to capture surface runoff would help reduce the pressure on well water utilization Talbot 1926 . Simple small earthen dams placed across drainage ways can provide open water storage
