The work upon which this report is based done under a co-operative agreement between the Idaho State ard of Laud Commissioners and the Office of i Experiment PUS, United States Department of Agriculture. DUTY OF WATER INVESTIGATIONS DON H. BARK IRRIGATION ENGINEER IN CHARGE OF IRRIGATION INVESTIGATIONS IN IDAHO. OFFICE OF EXPERIMENT STATIONS, U. S. DEPARTMENT OF AGRICULTURE. The work upon which this report is based was done under a co-operative agreement between the Idaho State Board of Land Commissioners and the Office of Experiment Stations, United States Department of Agriculture. , -s5V , e 3 DUTYOFWATERINVESTIGATION BY DON H. BARK. I IRRIGATION ENGINEER, IN CHARGE OF IRRIGAlON INVESTIGATIONS lW IDAHO. OFFICE OF EXPERIMENT STATIONS, U. S. DEPARTMENT OF AGRICULTURE. The Idaho State Board of Land CommiSvsioners entered into a co-operative agreement with the Irrigation Investigations of the Office of Experiment Stations, U S. De- partment of Agriculture, late in the fall of 1909 for the purpose of conducting a Duty of Water investigation in Idaho. This agreement was renewed from year to year, the investigation having been conducted uninterruptedly during the seasons of 1910, 11, 12, and 13. The agreement under which the investigation was carried on provided that both parties should contribute equal amounts toward the investigation that the plans for the investigation be made and agreed upon by the Idaho State Engineer and the chief of Irrigation Investigations of the U. S. Department of Agriculture, and that the Idaho Agent of Irrigation Investigations should be charged with the carrying out of the investigation. The investigation has proved to be very popular with the irrigators of Idaho, eight of the larger irrigation companies of the State having contributed to the fund set aside for the purpose a total of almost f8,000.00 during the four years in order that the investigation might be extended. The reports of the investigation have also been much sought after, the demand during the past two years having far exceeded the available supply. The following report is based upon the results of the investigation during the four years, 1910 to 1913 inclusive, the investigation having covered the greater part of irrigated Idaho dur- ing the period. Duty of Water is a term that is used to express the relationship that exists between a given quantity of irrigation water and the area of land it is made to servo. The Duty is said to be high when a given quantity of water serves a comparatively large area of land, and low when it is made to serve only a comparatively small area, i. c., the Duty is the work the water is made to do. It is evident even to those unfamiliar with irrigation that different types of land and different kinds of crops will require different ainoits of water,-jand that all water rights should consist of amounts thaHt -would supply the actual requirements of .he.oife and crops in question and no more. The above is correct in theory, for ahe present area of arid land is fully twenty times that of the irrigated land, but to work it out in actual practice is a very difficult matter. Forty years ago there was but litle irrigated land in settlers knew Idaho, water was plentiful and the early nothing of the water requirements of soils and crops. They therefore filed upon and appropriated abnormally large amounts for the irrigation of their land in order to be sure of a sufficient amount. As time passed and settlement increased a better knowledge of the water requirements of soils was obtained, but even as late as ten years ago there was no real definite knowledge of nor standard practice in regard to the subject. Water rights of all kinds and sizes existed...