Publications—Water-Resources Investigations Report 93-4092
By S. William Wandle, Jr. and Allan D. Randall
U.S. Geological
Survey Water-Resources Investigations Report 93-4092
Revised 2007
The body of the report is available in PDF Format (7,341 KB)
Equations developed by multiple-regression analysis of data from 49 drainage basins in Massachusetts, New Hampshire, Rhode Island, Vermont, and southwestern Maine indicate that low flow of streams in this region is largely a function of the amount of water available to the basin and the extent of surficial sand and gravel relative to the extent of till and fine-grained stratified drift. Low flow per square mile from areas of surficial sand and gravel is consistently much greater than that from areas of till and bedrock, but flood plains and alluvial fans seem to contribute less low flow per square mile than do other types of surficial sand and gravel. The areal extent of lakes and swamps also correlates negatively with low flow in multiple-regression equations, presumably because intense evapotranspiration from these localities consumes water that would otherwise become streamflow.
The annual minimum 7-day mean low flows that occur during summer and fall at 2-year and 10-year recurrence intervals (7Q2 and 7Q10) were selected as indices of low flow and were adjusted to a common base period, 1942-71. Central New England was divided into a region of high relief that comprises much of New Hampshire, Vermont, and western Massachusetts, and a region of low relief that generally lies to the east and south but also includes the Lake Champlain lowland of Vermont. In the high-relief region, mean basin elevation proved to be the most significant index of the amount of water available. In the low-relief region, mean annual runoff per square mile was more significant than elevation, particularly when multiplied by the areal extent of sand and gravel and that of till. Dividing the areal extent of sand and gravel by stream length improved the fit of regression equations for the low-relief region.
Regression equations were developed that explained at least 95 percent of the variation in 7Q10 within both the high-relief and the low-relief data sets. Equations proposed for practical application were reasonably consistent with the statistical assumptions of least-squares analysis and yielded 7Q2 and 7Q10 values with standard errors of 1.9 and 1.4 cubic feet per second, respectively, for the high-relief region and 2.2 and 1.6 cubic feet per second for the low-relief region. When error was expressed as a percentage of each observed value, median errors were about 25 percent for 7Q2 in both regions, and about 25 and 55 percent for 7Q10 in the high- and low-relief regions, respectively. The equations do not apply to basin segments that are substantially affected by urbanization, stream regulation, or ground-water withdrawals, and may not be appropriate where basin characteristics fall outside their range in the data set or where the geologic and topographic maps needed for measurement of basin characteristics are unavailable, or are of small scale or mutually inconsistent.
Abstract
lntroduction
Spatial Variability of Low Flows of Streams in Central New England
Environmental Characteristics That Cause Variability
Water Availability
Surficial Geology
Lakes and Swamps
Underflow
Bedrock
Urbanization and Regulation
Previous Studies of Low-Flow Variability
Examples of Low-Flow Variability
Quantitative Analysis of the Effects of Surficial Geology, Lakes and Swamps, Annual Water
Availability, and Related Variables on Low Flows
Selection of a Representative Set of Basins
Computation of Low Flows From Streamflow Records
Selection of Reference Period
Methods Used to Compute Low-Flow Statistics
Adjustments to Eliminate Effects of Regulation
Measurement of Environmental Characteristics of Basins in the Data Set
Surficial Geology
Lakes and Swamps
Annual Water Availability and Topography
Application of the Multiple-Regression Technique
Division of Central New England into Regions of High and Low Relief
Interpretation of Regression Equations
High-Relief Region
Effects of Environmental Characteristics on Low Flows
Effects of Scale Transformations and Data Distribution on the Interpretation
Selection of Equations for Practical Application
Low-Relief Region
Effects of Environmental Characteristics on Low Flows
Effects of Scale Transformations and Data Distribution on the Interpretation
Selection of Equations for Practical Application
Application of Regression Equations to Estimate Low Flow at Ungaged Sites
Accuracy and Limitations
Estimation Procedure
Sample Computation
Summary and Conclusion
References
5-6 . Graphs showing:
| 5. | Seven-day low-flow frequency curve for North Branch Hoosic River at North Adams, Mass. | |
| 6. | Relation between annual mean 7-day low flows at an index station (West Branch Westfield River) and those at a short-term station (Bassett Brook). | |
| 7. | Map showing locations of regions of high and low relief. |
8-10 . Graphs showing relation of observed low flows in high-relief region to low flows estimated from:
| 8. | Equations 4B and 7B. | |
| 9. | Equations 9A and 9B. | |
| 10. | Equations 10B and 12B. | |
| 11. | Graph showing standard error of logarithmic regression equations for high-relief region as a function of weighting factor applied to area of coarse stratified drift. | |
| 12. | Graph showing correlation between mean runoff determined by two alternative methods for all basins in the low-relief data set that have more than 10 years of streamflow record. |
13-15 . Graphs showing relation of observed low flows in low-relief region to low flows estimated by:
| 13. | Equations 16B and 18B. | |
| 14. | Equations 19A and 19B. | |
| 15. | Equation 20B. | |
| 16. | Graph showing standard error of logarithmic regression equations for the low-relief region as a function of weighting factors applied to area of coarse stratified drift and areas of lakes, swamps, and alluvium. | |
| 17. | Example of surficial geologic map delineating geologic units used to estimate low flow in the high-relief region. |
Wandle, S.W., and Randall, A.D., 1993, Effects of Surficial Geology, Lakes and Swamps, and Annual Water Availability on Low Flows of Streams in Central New England, and Their Use in Low-Flow Estimation: U.S. Geological Survey Water-Resources Investigations Report 93-4092, Revised 2007, 57 p.
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