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<br />001242 <br /> <br />. <br /> <br />LIMITATIONS IN HYDROLOGIC DATA AS APPLIED TO <br />STUDIES OF WATER CONTROL AND WATER MANAGmENT <br />INTRODUCTION <br /> <br />BACKGROUND <br /> <br />Hydrologic studies COMMonly derive from records of numerous <br />variables, including: <br /> <br />Insolation and radiation <br />Air temperature <br />Humidity <br />Wind . <br />Precipitation <br />Rain <br />Snow <br />Evaporation and transpiration <br /> <br />Streamflow <br />Storage in reservoirs and lakes <br />Soil water <br />Gro1Uld water <br />Water quality. physical. chemical <br />and biologic <br />Sediment transport and deposition <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 of <br />a particular study in every respect. Both systematic and random errors <br />must be exp~cted. Some of these may compensate over a period of time; <br />others may not. Also, the records of certain variables involve inherent <br />limitations that may influence greatly the strength of the conclusions <br />derived. <br /> <br />Few if any of the variables listed above are independent; several <br />of them are influenced substantially by other, non-hydrologic variables <br />including character of vegetal cover, physical properties of soil and <br />rocks, and relief and orientation of topographic features with respect <br />to wind movement and storm tracks. Such related. but primarily non- <br />hydrologic variables are not a topic of further discussion in this manual, <br />which is addressed primarily to the novice hydrologist and which seeks <br />to (1) point out inherent limitations in hydrologic records; (2) identify <br />common sources of error in those records; and (3) where feasible, outline <br />procedures for discriminating data that seem to be abnormal and possibly <br />in error. Assuming that a specific cause can be identified. presumably <br />erroneous or inconsistent data sometimes can be adjusted reasonably; <br />otherwise. they may be excluded from further consideration. However. <br />adjustment and exclusion must be cautious and in conformity with sound <br />methods of statistics, lest the hydrologist trap himself into the funda- <br />mental error of accepting only.data that fit a favored hypothesis. <br /> <br />;',."" -- ~._ _",,,",... '_4;,; H ",~,__..i..__ <br /> <br />