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<br />001446 <br /> <br />LIMITATIONS IN HYDROLOGIC DATA AS APPLIED TO <br /> <br />STUDIES OF WATER CONTROL AND WATER MANAGEMENT <br /> <br />INTRODUCTION <br /> <br />BACKGROUND <br /> <br />Hydrologic studies commonly derive from records of numerous <br />variables, including: <br /> <br />Stremft:rlow <br />storage in reservoirs and lakes <br />Water quality, chemical and biologic <br />Sedimentation <br />Ground water <br />Soil "Water <br />Precipitation <br />Rain <br />Snow <br /> <br />Temperature <br />Air <br />Water <br />Soil <br />Wind <br />Humidity or water vapor <br />Insolation and radiation <br />Evaporation and transpiration <br /> <br />No such records, especially those spanning a long term of years, <br />should be accepted at face value and assumed to satisfy the purposes <br />of a particular study in every respect. Both systematic and random <br />errors must be expected. Some of these may compensate over a period <br />of time; ot.hers may not. Also, the records of certain variables involve <br />inherent limitations that may influence greatly the strength of the <br />conclusions derived. <br /> <br />The variables listed above are hydrologic per se. Few if any of <br />them are independent; several of them are influenced substantially by <br />other, non~hydrologic variables including character of vegetal cover, <br />physical properties of soil and rocks, and relief and orientation of <br />topographic features with respect to wind movement and storm tracks. <br />Such related, but primarily non-hydrologic variables are not a topic <br />of further' discussion in this manual, which is addressed to the novice <br />hydrologist and which seeks to (1) point out inherent limitations in <br />hydrologic records; (2) identify common sources of error in those records; <br />and (3) where. feasible, outline procedures for discriminating data that <br />seem to be ' abnormal and possibly in error. Assuming that a specific cause <br />can be identified, presumably erroneous or inconsistent data sometimes cah <br />be adjustecl reasonably; otherwise, they may be excluded from further <br />consideration. However, adjustment and exclusion must be cautiouscand in <br />conformity,with sound methods of statistics, lest the hydrologist trap <br />himself into the fundamental error of accepting' only data that fit a <br />favored hypothesis. <br /> <br />J. c, <br /> <br />