Some Relations Between Streamflow Characteristics and the Environment in the Delaware River Region GEOLOGICAL SURVEY PROFESSIONAL PAPER 417-B Some Relations Between Streamflow Characteristics and the Environment in the Delaware River Region By A. G. HELY and F. H. OLMSTED CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 417-B UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 CONTENTS Page Page Abstract___._______________________________ Bl Streamflow parameters Continued Introduction ___-__-__-__---__-_--_____-__--___-____ 1 Flow-duration characteristics Continued Meteorological and terrestrial environments__--___-_-__ 2 Residual effect of basin size on Qw. ___________ Bll Streamflow parameters____----_____-_____-_-__-_____ 4 Flow-frequency characteristics.___________________ 13 Average annual runoff._-_____-_-____-__-_-_-____ 4 Base-flow characteristics.________________________ 14 Flow-duration characteristics_____________________ 8 Methods of relating base-flow recession curves.. 15 Relations between Qoo and average annual pre­ Relations between base-flow parameters and cipitation. _______________________________ 9 average annual precipitation____-_______-_- 16 Relations between Qw/Qa and average annual Relations between geology and streamflow in a region of precipitation _____________________________ 9 complex geology and relatively uniform precipitation. _ 17 Relations between Qw and average annual dis­ Conclusions ________________________________________ 24 charge_________________________________ 9 References.________________________________________ 25 ILLUSTRATIONS [Plates are in pocket] PLATE 1. Map of Delaware River region showing physiographic units and locations of gaging stations. 2. Generalized map of pre-Quaternary geology of 24 drainage basins in Delaware River region. Page FIGURE 1. Relations between average annual runoff and precipitation.___________ B7 2. Relations for obtaining daily flow at the 90 percent duration point from monthly flow____________-_-_--_______-__-__-__--___-____-___ 8 3. Relations between Qw and average annual precipitation.______________ 10 4. Relations between Qm/Qa and average annual precipitation. ___________ 11 5. Relations between Qw and average discharge._______________________ 12 6. Residual effect of basin size on Q9o_-__-__-_-___--_-__-____---___--- 12 7. Comparison of minimum 7-day flow and <?9o----_--------_----------- 13 8. Relations between minimum 7-day flow and average annual precipita­ tion, _________________________________________________________ 14 9. Diagram showing a method of relating base-flow recession curves. _____ 16 10. Relations between summer runoff from natural storage and average annual precipitation__________________________________________ 17 TABLES TABLE 1. Gaging stations, drainage areas, precipitation and streamflow parameters. B5 2. Physiographic and geologic classifications of 24 drainage basins__-__- 19 3. Physical and hydrological characteristics of geologic units._________ 20 4. Stream density of 19 drainage basins, classified according to geologic units._ _______________________________________________________ 22 5. Land slope of 19 drainage basins, classified according to geologic units.- 22 ni CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY SOME RELATIONS BETWEEN STREAMFLOW CHARACTERISTICS AND THE ENVIRONMENT IN THE DELAWARE RIVER REGION By A. G. HELT and F. H. OLMSTED ABSTRACT of Qm/Qa for each major geologic unit were determined from Streamflow characteristics are determined by a large number streamflow records. From these values and the percentage of of factors of the meteorological and terrestrial environments. area represented by each unit, a ratio for each gaging station Because of lack of quantitative data to describe some of the was computed. Comparison of these computed results with the factors and complex interrelations among them, complete anal­ observed results indicates that nearly all of the variation in the ysis of the relations between streamflow and the various en­ ratio is associated with variation in geology. vironmental factors is impossible. However, certain simplify­ The investigation indicates that the original assumptions are ing assumptions and generalizations made possible a partial correct; average precipitation is the principal meteorological analysis for the Delaware River region. influence and geology is the principal terrestrial influence. To­ For relations involving average runoff or low-flow param­ gether these two factors account for a very large proportion of eters, average annual precipitation was assumed to be the prin­ the variation in average runoff and low-flow characteristics. cipal meteorological factor, and geology (a complex of many factors) was assumed to be the principal terrestrial influence, INTRODUCTION except for that of basin size which was largely eliminated by The quantity and distribution of water in the hy- expression of discharge in terms of unit area. drologic cycle of any region are determined by the me­ As a first approximation, physiographic units were used as a basis for classifying the geology. Relations between flow teorological and terrestrial environments. Many char­ parameters and precipitation are fairly well defined for some acteristics of these environments influence streamflow, physiographic units, but not for those in which the geology and although some of the characteristics can be meas­ varies markedly or the areal variation in average precipitation ured, others can only be described. Interrelations is very small. These relations provide a basis for adjusting the among the characteristics, and changes resulting from flow parameters to reduce or eliminate the effects of areal variations in precipitation and increase their significance in man's activities, add to the difficulty of analysis. As studies of the effects of terrestrial characteristics. a result, for large areas, knowledge of the relations An investigation of the residual effect of basin size (the between streamflow characteristics and environment effect remaining when discharge is expressed in terms of unit tends to be qualitative rather than quantitative. Quan­ area) on relations between flow parameters and average pre­ titative results have been obtained for some relations cipitation indicates that such effect is negligible, except for very large differences in area. but these are limited to small, experimental water­ Parameters that are derived from base-flow recession curves sheds. and are related to a common discharge per unit area have in­ This report presents results of a study of relations herent advantages as indicators of effects of terrestrial char­ between streamflow characteristics, particularly low acteristics of basins, because the.y are independent of areal flows, and the most significant characteristics of the en­ variations in average annual precipitation. Winter base-flow parameters are also practically independent of the effects of vironment. Relations for the entire study area are ex­ evapotranspiration from ground water. However, in many amined first. These must necessarily be based on a parts of the region these advantages are reduced or nullified by highly generalized classification of terrestrial charac­ the difficulties of defining base-flow recession curves, particu­ teristics (physiographic provinces and subprovinces). larly winter curves, with sufficient accuracy. Therefore, a more detailed classification of geology in In the absence of suitable base-flow recession data and a suit­ able basis for adjusting parameters, the ratio of the discharge a part of the area that is characterized by large differ­ equaled or exceeded 90 percent of the time to the average dis­ ences in geology but small differences in average annual charge (Qtt/Qa), or a similar duration parameter, probably is precipitation was made so that a better comparison of the best indicator of the influence of terrestrial character­ geologic characteristics and streamflow could be made. istics, although the ratio may vary somewhat with average Although geology is a complex of many separate fac­ precipitation. In a part of the region where geologic differences are large tors, it was necessary to resort to the simplification of and areal variations in average precipitation are small, values treating geology as a single factor in parts of the study. Bl B2 CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY Because of the many factors that affect streamflow, subf reezing temperatures is a season of relatively high the relations developed are not independent of influ­ runoff. The effect on annual evapotranspiration, which ences not considered in the analysis; they are compa­ ranges from 18 inches in the northern part of the area to rable to first approximations in a multiple correlation. about 27 inches x in the southern part, is more significant. Lack of sufficiently detailed information to complete As streamflow is the residual of precipitation minus the correlation generally precludes much refinement of evapotranspiration (or water loss if underground out­ the first approximations. Nevertheless, the authors be­ flow is significant), the relations between some stream- lieve that the relations developed contribute to better flow parameters and precipitation include effects of understanding of