Vermont Stream Geomorphic Assessment Appendix J Vermont Regional Hydraulic Geometry Curves River Management Program Vermont Water Quality Division November, 2001 Natural Resources - J0 - VT Agency of
Background Bankfull hydraulic geometry relationships, otherwise known as regional curves were presented by Dunne and Leopold in (1978). They found bankfull stage to correspond to the discharge at which channel maintenance is the most effective, that is, the discharge at which moving sediment, forming or removing bars, forming or changing bends and meanders, and generally doing work that results in the average morphologic characteristics of channels. The bankfull stage and its attendant discharge serve as consistent morphological indices which can be related to the formation, maintenance, and dimensions of the channel as it exists under modern climatic regime (Rosgen 1996). Since Dunne and Leopold=s presentation of regional curves in 1978 other research efforts have led to the development of regional curves for many areas of the United States. Regional curves have been developed in eastern states including: Maryland, Pennsylvania, North Carolina and the Catskill region of New York. In these states and others, regional curves have proven to be an invaluable tool for use in river assessment, protection, restoration and general management. Protocols Selection of Study Gages Study gages were selected from the list of active USGS streamflow gages with the following considerations in mind: the presence and magnitude of flow regulation above the gage; size of the drainage area; the period for which flow data is available; and the presence of significant tributaries entering in the vicinity of the gage. The following data was acquired from the USGS for each of the study gages: 9-207 forms Asummary of discharge measurements@, Log Pearson annual frequency analyses, discharge rating curves and gage location and description forms. Field Surveys The first field task was to delineate the study reach. Ideally study reaches were 20 bankfull widths in length with the gage located at the midpoint. A reach would begin and end at the same bed feature type (i.e., riffle head to riffle head). At several gages, where there was a significant change in stream morphology within the reach, the extent of the study reach was shorter than 20 channel widths in length and/or the gage was not located at the center of the reach. Following delineation of the study reach morphological features indicating bankfull stage were identified and flagged. Where possible, bankfull indicators were identified every bankfull width. Areas of bedrock, rip rap, bridge footings or other physical constraints were avoided when identifying bankfull features. Developed flood plain on the inside of meanders and developing point bars were considered good indicators and weighted more heavily than erosion or scour features along the outside of meander bends. For extensive discussion on the identification of bankfull indicators and the processes that create these indicators see Leopold and Maddock (1953); Emmett (1975); Harrelson et.al. (1994); Rosgen (1996). Next, the longitudinal profile of the channel was surveyed capturing thalweg and water surface elevations at the head of each riffle, run, pool, pool max depth, and glide. Water surface and bankfull stage elevations were surveyed at each identified bankfull indicator. The elevation of water surface was surveyed at the staff plate, or intake orifice when the staff plate was not present, and river stage as indicated by the staff plate was recorded. During the identification of bankfull indicators locations appropriate for a cross sectional surveys and pebble counts were chosen. Stable riffles, preferably cross overs, representative of the study reach were selected for cross section surveys. Following the longitudinal survey, cross-sectional surveys were conducted at the pre-determined locations. Crosssectional surveys at riffles extended beyond the bankfull channel to include the flood prone area in order to measure the width of flood prone area and calculate the degree of entrenchment (Rosgen 1996). The elevations of bankfull stage, water surface and maximum depth were also captured in the survey. A Modified Wolman Pebble Count (Rosgen 1996) was conducted for purposes of reach classification. Transect pebble counts were conducted at the locations of each cross sectional survey and at each bed feature type. The interval between observations within a transect was set such that no individual particle would represent more than 5% of the cross sectional width. - J1 -
Photographs were taken upstream and downstream from the gage location. Photos were also taken of each cross section surveyed and of clear bankfull indicators. Data Analysis The first step in data analysis was to identify bankfull discharge and determine its recurrence interval (R.I.). From the data provided by the longitudinal survey the bankfull stage elevation was converted to gage height. Next, the bankfull gage height was compared to the stage/discharge rating curve for the gaging station to identify the bankfull discharge. The recurrence interval of the bankfull discharge was determined using the flood frequency relationship derived for the gaging station (Table 1). Next, parameters collected for the purpose of stream classification and shown in Table 2 were used to classify each study reach according to the Rosgen classification system (Rosgen 1996). Finally, bankfull discharge for the gaging station was plotted against drainage area at the gaging station. Bankfull width, mean depth and cross sectional area were also plotted against drainage area at the gaging station (Figure 1). Table 1 Regional Curve Dataset USGS Period of Drainage R.I. Of Qbkf XS Area Width Gage Name Gage # Record (yrs.) Area (sq.mi.) Qbkf (cfs) (yrs.) (sq.ft.) (ft.) Depth (ft.) East Orange Br. 01139800 42 8.9 186.5 1.44 52.8 28.1 1.9 Ottaquechee 01150900 16 23.4 661.0 1.43 201.3 62.5 3.2 Ayers 01142500 61 30.5 621.0 1.65 146.0 41.0 3.6 Sleepers R. 01135300 10 42.9 1312.0 1.40 213.5 68.6 3.1 Laplatte 04282795 10 44.6 734.0 1.49 197.2 77.4 2.5 Little Otter 04282650 10 57.1 853.6 1.55 264.6 91.7 2.9 E Br Passumpsic 01133000 40 53.8 1122.0 1.62 224.3 71.5 3.1 Mettawee 04280350 16 70.2 3300.0 1.65 337.0 95.3 3.5 Dog 04287000 66 76.1 1537.0 1.12 277.0 78.0 3.6 Lewis 04282780 10 77.2 1850.0 1.61 244.0 88.7 2.7 Walloomsac 01334000 69 111.0 1879.0 1.12 410.0 110.0 3.7 Williams 01153550 14 112.0 5490.0 1.86 650.3 132.5 4.9 Black River 04296000 49 122.0 1726.0 1.41 303.7 70.6 4.3 Mad River 04288000 72 139.0 4960.0 1.52 559.0 138.0 4.0 Table 2 Stream Classification Data USGS Gage # Entrenchment W/D Reach Slope (ft./ft/) D50 Stream Type Ayers Brook 01142500 1.2 11 0.00077 0.3 Gc Black River 04296000 2.8 16 0.00040 9.9 C4c Dog River 04287000 2.3 22 0.00080 37 C4 East Orange Br. 01139800 4.8 15 0.01320 15.7 C4b Laplatte 04282795 1.6 30 0.00100 16.2 B4c Lewis 04282780 4.2 32 0.00440 52.4 C4 Little Otter 04282650 2.5 32 0.00196 0.8 C5 Mad River 04288000 2.8 34 0.00200 20.5 C4 Mettawee 04280350 2.4 30 0.00580 27.4 C4c Ottaquechee 01150900 3.1 19 0.00173 10.4 C4 E Br Passumpsic 01133000 2.7 23 0.00530 56 C4 Pope 01135150 1.7 11 0.02400 19 B4 Sleepers R. 01135300 3.0 22 0.00066 16.8 C4c Walloomsac 01334000 6.6 30 0.00210 43.6 C4 Williams 01153550 1.4 22 0.00250 58.9 B4c - J2 -
Vermont 2002 Regional Hydraulic Geometry Curves (provisional) 10000.0 1000.0 Qbkf (cfs) XS Area (sq.ft.) Q = 17.69DA 1.07 R 2 = 0.81 Depth (ft.) / Width (ft.) / XS-Area (sq. ft.) / Discharge (cfs) 100.0 10.0 1.0 Width (ft.) A = 12.21DA 0.75 Depth (ft.) R 2 = 0.85 W = 10.18DA 0.50 R 2 = 0.78 D = 1.22DA 0.25 R 2 = 0.59 1.0 10.0 100.0 1000.0 Drainage Area (sq. mi.) Figure 1 Vermont Regional Hydraulic Geometry Curves Note: These curves are provisional. Until the curves undergo field testing and peer review, caution is advised when using them for channel design purposes. Also, curves should only be used on streams of similar type and in similar hydrophysiographic settings as those from which the data was collected. The curves should not be applied to flow or sediment regulated streams (i.e. below flow regulating dams). - J3 -
It has been the experience of the Vermont River Corridor Management Section that the 2001 Regional Curves have been used in the field most commonly as a predictor of channel width. To improve the usability of the curves for this purpose we have provided confidence bands for the width vs. drainage area relation. Confidence bands for the other relations are available upon request. Figure 2. 95% Confidence Bands for Width vs. Drainage Area Relation Note: Confidence bands developed using Sigma Plot 2000. - J4 -
Future Study The Vermont River Management Program plans to continue to work with its partners to further develop and refine the regional curves. Future work will include the following: additional gaging stations in Vermont and adjacent regions, that meet selection criteria, will be surveyed and added to the regional curve plot; work will be done to stratify the data set by stream type, valley characteristics and hydro-physiographic regions within VT and surrounding regions as the regional curve data set becomes sufficient to do so; and validation checks as reference reach data is obtained from other stream reaches. References 1. Emmet, William. 1975. The Channels and Waters of the Upper Salmon River Area, Idaho. U.S. Geological Survey Professional Paper 870-A. U.S. Department of the Interior, USGS. 116p. 2. Harrelson, Cheryl C., Rawlins C.L., and Potyondy, J. 1994. Stream channel reference sites: an illustrated guide to field technique. General Technical Report RM-245. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 61p. 3. Leopold, Luna, Maddock, Thomas. 1953. The Hydraulic Geometry of Stream Channels and Some Physiographic Implications. U.S. Geological Survey Professional Paper 252. U.S. Department of the Interior, USGS. 57p. 4. Rosgen, David. 1996. Applied River Morphology. Printed Media Companies, Minneapolis, MN. Partners and Supporting Agencies United States Forest Service, Green Mountain National Forest. United State Fish and Wildlife Service, Region 5; Partners for Fish and Wildlife. United States Geological Survey, New Hampshire/Vermont District. Natural Resource Conservation Service, Vermont. Vermont Department of Fish and Wildlife. Acknowledgments We would like to thank Dan McKinley of the Green Mountain National Forest, Rochester District and Eric Derleth of the US Fish and Wildlife Service, Region 5 for committing resources of their respective programs as well as their personal energies, without which this project would not have been started or completed. Thanks also goes out to Christa Alexander of the VT Fish and Wildlife Department for her participation in field efforts. Her knowledge of river systems, from both a physical and biological perspective, was essential to this project. And finally, special thanks to Staci Pomeroy of VT Water Quality Division for her work both in the field and in front of the computer. Staci=s dedication and inquisitive nature greatly benefitted the regional curve study. For more information contact: Shayne Jaquith shayne.jaquith@anr.state.vt.us (802) 241-4456 or Mike Kline mike.kline@anr.state.vt.us (802) 241-3774 - J5 -