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HomeMy WebLinkAboutSuWa98Alaska Resources Library & Information Services Susitna-Watana Hydroelectric Project Document ARLIS Uniform Cover Page Title: 2012 reconnaissance-level geomorphic and aquatic habitat assessment of project effects on lower river channel SuWa 98 Author(s) – Personal: Author(s) – Corporate: [Alaska Energy Authority] AEA-identified category, if specified: 2012 Environmental Study Plans AEA-identified series, if specified: Series (ARLIS-assigned report number): Susitna-Watana Hydroelectric Project document number Existing numbers on document: Published by: [Anchorage, Alaska : Alaska Energy Authority, 2012] Date published: May 2, 2012 Published for: Date or date range of report: Volume and/or Part numbers: Final or Draft status, as indicated: Document type: Pagination: 10 p. Related work(s): Pages added/changed by ARLIS: Notes: All reports in the Susitna-Watana Hydroelectric Project Document series include an ARLIS- produced cover page and an ARLIS-assigned number for uniformity and citability. All reports are posted online at http://www.arlis.org/resources/susitna-watana/ Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 1 2012 RECONNAISSANCE-LEVEL GEOMORPHIC AND AQUATIC HABITAT ASSESSMENT OF PROJECT EFFECTS ON LOWER RIVER CHANNEL INTRODUCTION The Alaska Energy Authority (AEA) is preparing a License Application that will be submitted to the Federal Energy Regulatory Commission (FERC) for the Susitna-Watana Hydroelectric Project (Project), using the Integrated Licensing Process (ILP). The Project is located on the Susitna River, an approximately 300-mile-long river in the Southcentral region of Alaska. The Project’s dam site will be located at river mile (RM) 184. The results of this study and of other proposed studies will provide information needed to support FERC’s National Environmental Policy Act (NEPA) analysis for the Project license. Construction and operation of the Project as described in the Pre-Application Document (PAD; AEA 2011) will affect the timing and magnitude of flow, sediment supply, and sediment transport capacity, which have the potential to alter aquatic habitat and channel morphology in the Lower Susitna River. Understanding existing aquatic habitat and geomorphic conditions, how those conditions change over a range of stream flows, and how stable/unstable the conditions have been over recent decades will provide a baseline that will be needed to predict potential aquatic habitat and geomorphic changes that could occur due to the Project. The types, magnitudes, and extents of Project impacts on morphology are influenced by water and sediment inflow from tributaries downstream of the Project and the geology through which the river flows. As major tributaries join the Susitna, the impact of the dam on hydrology and sediment supply can be attenuated by the flow and sediment contributions from the tributaries. Two major tributaries, the Talkeetna and Chulitna Rivers, approximately double the flow near the upper end of the Lower River. These tributary influences result in the Lower River exhibiting different geomorphic characteristics than the Middle River and may lead to different responses to the Project than may occur in the Middle River. STUDY OBJECTIVE The objective of this study is to assess at a reconnaissance level the potential for the Project to affect aquatic habitat and channel morphology in the Lower Susitna River. The specific objectives are as follows:  Evaluate the relative magnitude of changes to the flow regime pre- and post-Project;  Assess potential changes to channel morphology and aquatic habitat pre- and post- Project;  Evaluate the relative magnitude of changes to the sediment regime pre- and post- Project, the potential impacts on sediment/substrate gradations, and the vertical and lateral stability of the channel;  Delineate large-scale geomorphic river segments with relatively homogeneous characteristics (e.g., channel width, lateral confinement by terraces, entrenchment ratio, Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 2 sinuosity, slope, bed material, single/multiple channel, hydrology) for the purposes of stratifying the river into study segments;  Conduct a geomorphic assessment of historic channel change and its drivers as well as determine whether changes have affected the frequency and distribution of meso-habitat units; and  Provide information to assist AEA and licensing participants to develop the 2013-2014 study plans. STUDY AREA The study area includes the Lower Susitna River from the mouth of the river at Cook Inlet (RM~ 0) upstream to and including the three rivers confluence (RM~98). NEXUS BETWEEN PROJECT AND RESOURCE TO BE STUDIED AND HOW THE RESULTS WILL BE USED Project operations will change the timing and magnitude of flow, sediment supply and sediment transport capacity which have the potential to alter channel morphology and aquatic habitat in the Lower River. Results of this study will provide the initial basis for assessing the potential for changes to the Lower River reach morphology due to the Project. Additional studies will be planned for 2013-2014 if the results of this study identify a potential for channel adjustments and associated changes to important aquatic habitat in response to the Project. Issues associated with geomorphic resources in the Lower River reach for which information appears to be insufficient were identified in the PAD (AEA 2011), including:  G16: Potential effects of reduced sediment load and changes to sediment transport as a result of Project operations within the Lower River.  F19: The degree to which Project operations affect flow regimes, sediment transport, temperature, water quality that result in changes to seasonal availability and quality of aquatic habitats, including primary and secondary productivity. EXISTING INFORMATION An analysis of the Lower River reach and how riverine habitat conditions change over a range of stream flows was performed in the 1980s using aerial photographic analysis (R&M Consultants, Inc. and Trihey and Associates 1985a). This study evaluated the response of riverine aquatic habitat to flows in the Lower River reach between the Yentna River confluence (RM 28.5) and Talkeetna River confluence (RM 98) (measured at Sunshine gage RM ~84) ranging from 13,900 cfs to 75,200 cfs. The study also included an evaluation of the morphologic stability of islands and side channels by comparing aerial photography between 1951 and 1983. In another study, 13 tributaries to the Lower River reach were evaluated for salmon spawning access under existing and proposed stream flows for the original hydroelectric project in the 1980s (R&M Consultants, Inc. and Trihey and Associates 1985b). The study report contains information regarding run timing, mainstem and tributary hydrology, and morphology. Based on the results of this study it was concluded that passage for adult salmon was not restricted under Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 3 natural flow conditions nor was passage expected to become restricted under the 1980s proposed Project operations. The AEA Susitna Water Quality and Sediment Transport Data Gap Analysis Report (URS 2011) states that “if additional information is collected, the existing information could provide a reference for evaluating temporal and spatial changes within the various reaches of the Susitna River.” The gap analysis emphasizes that it is important to determine if the conditions represented by the data collected in the 1980s are still representative of current conditions, and that at least a baseline comparison of current and 1980s morphological characteristics in each of the identified subreaches is required. This comparison should include not only identification of changes, but should consider if the relative proportion of the various meso-habitat types have remained constant within a reach. METHODS Work conducted for the 2012 Reconnaissance-Level Geomorphic and Aquatic Habitat Assessment of Project Effects on Lower River Channel study will quantify the magnitude of change associated with stream flow, riverine habitat features, and sediment transport under the existing pre-Project and proposed post-Project conditions. In addition, a geomorphic assessment of channel change will be conducted. The following sections describe the specific analyses that will be performed. Stream Flow Assessment Comparison of Pre- and Post-Project Stream Flow Pre-Project and available post-Project (proposed) hydrologic data will be compared. This will include a comparison of the monthly and annual flow duration curves (exceedance pots) and plots/tables of flows by month (maximum, average, median, minimum) for the Susitna River at the Sunshine and Susitna Station gaging stations. Additional hydrologic indicators may be used to further illustrate and quantify the comparison between pre- and post-Project stream flows. The pre-Project data analysis will include the extended record being prepared by the U. S. Geological Survey (USGS). Comparison of Pre- and Post-Project Flood Frequency and Flood Duration at the Sunshine and the Susitna Station Gages Using the extended record currently being prepared by the USGS, a flood-frequency and flood- duration analysis for pre- and post-Project annual peak flows will be performed. The flood- frequency analysis will be performed using standard hydrologic practices and guidelines as recommended by USGS (1982). Riverine Habitat-Flow Relationship Assessment River Stage A tabular and graphical comparison of the change in water surface elevations associated with the results of the pre- and post-Project stream flow assessment (above) will be developed using the stage-discharge relationships (rating curves) for the Sunshine and Susitna Station gaging stations. This comparison will include monthly and annual stage duration curves (exceedance Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 4 plots) and plots/tables of stage by month (maximum, average, median, minimum). Additional parameters to describe and compare the pre- and post-Project water surface elevations may be performed. A graphical plot of a representative cross section at each gaging station will be developed with a summary of the changes in stage (i.e., water surface elevation) for the two flow regimes. If the historic gage shift information is available, a specific gage analysis will be conducted to determine the relative stability of the channel section at the two gaging stations. If possible, the location of the active channel and the floodplain will also be identified on the cross section. The availability of USGS winter gage data with respect to discharge and ice elevation/thickness will be investigated. Coordination with the WR-S2: Documentation of Susitna River Ice Breakup and Formation Study will occur to obtain information on ice elevation/thickness, as appropriate. An approximate analysis of discharge effects on ice elevation and cross-sectional flow characteristics (depth and velocity) at the USGS gage locations will be conducted, if feasible. This task will be coordinated with the Ice Processes Study. Synthesis of the 1980s Aquatic Habitat Information A synthesis/summary of the 1980s Response of Aquatic Habitat Surface Area to Mainstem Discharge Relationships in the Yentna to Talkeetna Reach of the Susitna River (R&M Consultants, Inc. and Trihey & Associates 1985a) will be provided. A synthesis/summary of the Assessment of Access by Spawning Salmon into Tributaries of the Lower Susitna River (R&M Consultants, Inc. and Trihey & Associates 1985b) will also be provided. Data will be summarized with respect to the anticipated pre- and post-Project flow changes, where applicable (see Stream Flow Assessment section above). Site Selection and Stability Assessment Up to eight sites in the Lower River will be selected from the Yentna to Talkeetna reach map book (R&M Consultants, Inc. and Trihey and Associates 1985a) at the ~36,600 cfs flow at Sunshine Gage to study in 2012. These sites will be selected in coordination with the Instream Flow Study, the Instream Flow Riparian Study, the Ice Processes Study and the stakeholders. A side-by-side comparison of the sites using the 1983 36,600 cfs aerials and the most appropriate current aerials or satellite imagery will be performed to qualitatively assess site stability. Sites which have been substantially reworked by the Susitna River since the 1980s will not be selected for comparison of riverine habitat in the 1980s versus the present. Only sites that have been relatively stable during the period will be selected. Aerial Photography Analysis, Riverine Habitat Study Sites (RM 28 to RM 98) Using GIS and the September 6, 1983 aerials for the 36,600 cfs flow, mainstem and side channel riverine habitat will be digitized from the 1985 map book (R&M Consultants, Inc. and Trihey and Associates 1985a) for the selected sites. Each area associated with a habitat type will be a polygon (without slivers). To provide a comparison with current conditions, either recent satellite imagery at a flow similar to 36,600 cfs or aerials obtained in 2012 (if appropriate satellite imagery is not available) will be used to delineate the current wetted areas within the riverine and side-channel habitats for the selected sites. Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 5 The difference in wetted surface area of the main channel and side-channel riverine habitats (as defined in R&M Consultants, Inc. and Trihey & Associates 1985a1) will be compared between the 1983 and current conditions. The areas of the riverine habitat types, along with the Geomorphic Assessment of Channel Change subtask (see below) will be compared and contrasted quantitatively and a qualitative assessment will be made of the similarity of the 1980s sites compared to the 2012 sites. The assessment of site stability will help determine the applicability of Lower River riverine habitat information developed in the 1980s to supplement information being developed in the current Project studies. Optional: Additional Aerial Photography Analysis, Riverine Habitat Study Sites (RM 28 to RM 98) Based on the results of the comparison of riverine habitat areas at the selected study sites for the Lower River and results of the Geomorphic Assessment of Channel Change subtask (see below), a determination of whether to perform a similar effort and comparison for up to two additional discharges will be made (discharges corresponding to the analysis of wetted habitat areas in the Lower River include 75,200 cfs, 59,100 cfs, 36,600 cfs, 21,100 cfs and 13,900 cfs). This decision will be made in coordination with the Instream Flow Study, Instream Flow Riparian Study, Ice Processes Study, Fish Study and stakeholders. If the decision is made to analyze riverine habitat at two additional discharges, the flows will be selected and the associated habitat areas digitized from the 1985 map book. Satellite imagery at similar discharges or new aerial photographs will be obtained (if appropriate satellite imagery is not available). The riverine habitat types will be delineated and digitized on these images to represent the current condition. The difference in wetted surface area of the main channel and side channel riverine habitats will be compared between the 1983 and current conditions for the two additional discharges. Sediment Transport Assessment Sediment Load Comparison The sediment transport measurements the USGS has collected will be used to develop bedload and suspended load rating curves to facilitate translation of the periodic instantaneous measurements into yields over longer durations (e.g., monthly, seasonal, and annual). Since gradations of transported material will be available, the data will allow for differentiation of transport by size fraction. Previous studies have documented the potential for bias in suspended load rating curves due to scatter in the relationship between sediment concentration or load and flow (Walling 1977a). Specifically, the bias can result from the construction of linear least-squares regression relationships of logarithmic transformed concentrations or loads and flows (Walling 1977b, Thomas 1985, Ferguson 1986). Various procedures are available to address the bias, including accounting for seasonal differences in sediment transport and accounting for hysteresis related to rising and falling limbs of flood hydrographs (Guy 1964, Walling 1974). Koch and Smillie (1986) and Cohn and Gilroy (1991) describe methods of handling the bias correction depending on the expected distribution of errors. The USGS Office 1 The geomorphic types are defined in: Response of Aquatic Habitat Surface Areas to Mainstem Discharge in the Yentna to Talkeetna-Reach of the Susitna River, Alaska, 1985, prepared by R&M Consultants, Inc. and Trihey & Associates (document No. 2774) for the Alaska Power Authority. Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 6 of Surface Water (1992) endorsed the recommendations in Cohn and Gilroy (1991) to use the Minimum Variance Unbiased Estimator (MVUE) bias correction for normally distributed errors, or the Smearing Estimator (Duan 1983) when a non-normal error distribution is identified. Once the sediment measurements are available for review, the potential for bias in the sediment rating curves will be considered and addressed as appropriate. The total sediment load delivered to the Lower River for pre- and post-Project conditions will be evaluated using the sediment rating curves developed from the historical data (and, if available in time, combined with any new sediment transport data being collected by the USGS for the Determine Bedload and Suspended Sediment Load by Size Fraction at Tsusena Creek, Gold Creek, and Sunshine Gage Stations study for the Sunshine and Susitna Station gaging stations). The total sediment load at the Sunshine and Susitna Station gaging stations will be compared for an average, wet, and dry year for pre-Project and adjusted post-Project using adjusted post-Project rating curves. The calculations will be based on the assumption that the post-Project sediment load at both gaging stations will be adjusted by reducing 100 percent of the total bedload and 90 percent of the total suspended load obtained from USGS measurements and the rating curve for the above Tsusena Creek gage if data are available, and if not, from the historical Gold Creek gaging station. Integrate Sediment Transport and Flow Results into Analytical Framework Based upon the above analyses, an assessment of anticipated Project effects on the Lower River channel type and morphology will be developed. Using the data developed for the pre- and post-Project flood frequency, flood duration, and sediment load analyses, the geomorphic response of the Susitna River in an analytic framework along the longitudinal profile of the river system from the three rivers confluence through Lower River reach will be predicted. The analytical framework developed by Grant et al. (2003) that relies on the dimensionless variables of (1) the ratio of sediment supply below the dam to that above the dam, and (2) the fractional change in frequency of sediment transporting flows will be used to predict the nature and magnitude of the Lower River geomorphic response. Other analytical approaches may be considered to demonstrate potential for geomorphic adjustments in the river reaches due to the Project. Geomorphic Assessment of Channel Change and Geomorphic Reach Delineation Compare Historic and Present-Day Channel Planform Pattern The 36,600 cfs September 6, 1983 set of Lower River aerial photographs and current satellite images or aerial photographs will be obtained to compare historical and present-day channel planform and pattern. Planform shifts of the main channel and side channels will be identified between the 1983 and current aerial photography. The three rivers confluence area is also a part of the analysis (extended to RM 99). Geomorphic features that are visible between the 1983 and current images, including the presence and extent of side channels, mid-channel bars, vegetated bar areas, and changes at tributary deltas will be mapped and characterized. Delineate Geomorphically Similar (Homogeneous) River Segments The Lower River (RM 0 to RM 98) will be delineated into large-scale geomorphic river segments (a few to many miles) with relatively homogeneous characteristics, including channel width, Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 7 entrenchment, ratio, sinuosity, slope, geology/bed material, single/multiple channel, braiding index and hydrology (inflow from major tributaries) for the purposes of stratifying the river into relatively homogeneous study segments. The first step in geomorphic reach delineation effort will be the identification of the system to classify and delineate the reaches. Numerous river classifications exist (Leopold and Wolman 1957; Schumm 1963, 1968; Mollard 1973; Kellerhals et al. 1976; Brice 1981; Mosley 1987; Rosgen 1994, 1996; Thorne 1997; Montgomery and Buffington 1997; Vandenberghe 2001), but no single classification has been developed that meets the needs of all investigators. Several factors have prevented the achievement of an ideal geomorphic stream classification, and foremost among these has been the variability and complexity of rivers and streams (Mosley 1987; Juracek and Fitzpatrick 2003). Problems associated with the use of existing morphology as a basis for extrapolation (Schumm 1991) further complicates the ability to develop a robust classification (Juracek and Fitzpatrick 2003). For purposes of classifying the Susitna River, available classification systems will be reviewed and it is anticipated that a specific system will be developed that borrows elements from several classifications system. The classification scheme will consider both form and process. Development of this system will be coordinated with the Instream Flow Study, Instream Flow Riparian Study, Ice Processes Study and Fish Study so it is consistent with their needs. These studies may require further stratification or lumping of the delineated reaches to identify specific conditions of importance to their effort, in which case these studies will further divide the river into subreaches or lump reaches. However, the overall reach delineations developed in the Geomorphology Study will be used consistently across all studies requiring geomorphic reach delineations. Since there are several studies that will require a reach delineation for planning 2012 field activities, an initial delineation based primarily on readily available information (most recent high quality aerials, bed profile from the 1980s, geomorphic descriptions from the 1980s) will be developed in April 2012. As additional information is developed—such as current aerials and transects—the delineation will be refined and the various morphometric parameters will be determined. Coordination with the WR-S1: River Flow Routing Model Transect Data Collection study will occur in order to obtain cross-section channel/floodplain data. Coordination with the Instream Flow Study, Instream Flow Riparian Study, Geomorphic Modeling Study and Ice Processes Study will occur to ensure that the river stratification is conducted at a scale appropriate for those studies. A reconnaissance-level site visit of the Lower River will be conducted that will be coordinated with other studies to take advantage of scheduled boat and helicopter trips as well as opportunities to coordinate with other studies. The purpose of this site visit will be to provide key Geomorphology Study team members an overview of the river system. STUDY PRODUCTS Study products to be delivered in 2012 will include the following: Summary of Interim Results. Interim reports will be prepared and presented to the Work Group to provide study progress. Reports will include up-to-date compilation and analysis of the data and ArcGIS spatial data products. Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 8 ArcGIS Spatial Products. Shapefiles with current riverine habitat types, the geomorphic assessment and the reach delineation will be created. All map and spatial data products will be delivered in the two-dimensional Alaska Albers Conical Equal Area projection, and North American Datum of 1983 (NAD 83) horizontal datum consistent with ADNR standards. Naming conventions of files and data fields, spatial resolution, and metadata descriptions will meet the ADNR standards established for the Susitna-Watana Hydroelectric Project. Technical Memorandum. A technical memorandum summarizing the 2012 results will be prepared and presented to resource agency personnel and other licensing participants, along with spatial data products. At a minimum, the technical memorandum will include:  Monthly and annual flow duration tables and curves for pre- and post-Project conditions.  Flood frequency and duration tables and curves for pre- and post-Project conditions.  Tabular and graphical curve comparison of the pre- and post-Project river stage for Sunshine and Susitna Station gaging stations.  Summarized historical information regarding the effects of stream flow on aquatic habitat.  Maps comparing present-day and historical (1980s) channel pattern and planform changes, including position of main and side channels, presence of mid-channel bars, vegetated bar areas, and tributary deltas.  Comparison of the relative proportion of the geomorphic features within each reach between present-day and the historical channel pattern.  Develop sediment rating curves for historical record and 2012 USGS data (if available).  Tabulation of the total sediment load comparing pre- and post-Project total sediment load for the Sunshine and Susitna gaging stations, for an average, wet, and dry year type.  Determination of the fractional change in sediment transporting flows pre- and post- Project and change in sediment supply pre- and post-Project applied to the Grant et al. (2003) analytical framework to predict magnitude and direction of potential geomorphic changes in the Lower River reach. SCHEDULE The following schedule for the 2012 scope of work is tentative. Milestone Date of Completion Summary of Interim Results May 21, June 29, and September 30, 2012 Final ArcGIS Spatial Products November 30, 2012 Final Technical Memorandum on 2012 Activity November 30, 2012 REFERENCES AEA (Alaska Energy Authority). 2011. Pre-Application Document: Susitna-Watana Hydroelectric Project FERC Project No. 14241. December 2011. Prepared for the Federal Energy Regulatory Commission by the Alaska Energy Authority, Anchorage, Alaska. Brice, J.C., 1981. Stability of relocated stream channels. Federal Highway Commission Report FHWA/RD-80/158, 177 p. Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 9 Cohn, T.A., and E.J. Gilroy. 1991. Estimating Loads from Periodic Records. U.S. Geological Survey Branch of Systems Analysis Technical Report 91.01. 81 p. Duan, N. 1983. Smearing Estimate: A Nonparametric Retransformation Method. Journal of the American Statistical Association, Vol. 78(383): 605–610. Ferguson, R.I. 1986. River Loads Underestimated by Rating Curves. Water Resources Research, Vol. 22(1): 74–76. Grant, G.E., J.C. Schmidt, and S.L. Lewis. 2003. A geological framework for interpreting downstream effects of dams on rivers. AGU, Geology and Geomorphology of the Deschutes River, Oregon, Water Science and Application 7. Guy, H.P. 1964. An Analysis of Some Storm-Period Variables Affecting Stream Sediment Transport. U.S. Geological Survey Professional Paper No. 462E. Juracek, K.E. and Fitzpatrick, F.A., 2003. Limitation and implications of stream classification. Jour. of American Water Res. Assn, v. 83, no. 3, June, pp. 659-670. Kellerhals, R., Church, M., and Bray, D.I., 1976. Classification and analysis of river processes. Jour. of Hydraulic Div. 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Prepared under contract to Harza-Ebasco, for Alaska Power Authority, document No. 2774, June. R&M Consultants, Inc. and Trihey & Associates. 1985b. Assessment of access by spawning salmon into tributaries of the Lower Susitna River. Prepared under contract to Harza- Ebasco, for Alaska Power Authority, document No. 2775, June. Susitna-Watana Hydroelectric Project FERC #14241 Alaska Energy Authority 2012 Lower River Geomorphology Study – May 2, 2012 Page 10 Rosgen, D.L., 1994. A classification of natural rivers. Catena. 22, pp. 169-199. Rosgen, D.L., 1996. Applied River Morphology. Wildland Hydrology, Inc., Pagosa Springs, CO. Schumm, S.A., 1963. A tentative classification of alluvial river channels. U.S. Geol. Survey Circ. 477, 10 p. Schumm, S.A., 1968. River adjustment to altered hydrologic regimen, Murrumbidgee River and paleochannels, Australia. U.S. Geol. Survey Prof. Paper 598, 65 p. Schumm, S.A., 1991. To Interpret the Earth. Cambridge Univ. Press, Cambridge, U.K., 133 p. Thomas, R.B. 1985. Estimating Total Suspended Sediment Yield with Probability Sampling. Water Resources Research, Vol. 21(9): 1381– 1388. Thorne, C.R., 1997. Channel types and morphological classification. In Thorne, C.R., Hey, R.D., and Newson, M.D. (eds), Applied Fluvial Geomorphology for River Engineering and Management. Chichester, Wiley, pp. 175-222. URS. 2011. AEA Susitna Water Quality and Sediment Transport Data Gap Analysis Report. Prepared by Tetra Tech, URS, and Arctic Hydrologic Consultants. Anchorage, Alaska. 62p.+Appendixes. USGS (U.S. Geological Survey ), 1982. Guidelines for determining flood flow frequency. Bulletin 17B, Hydrology Subcommittee, Interagency advisory committee on water data. USGS. 1992. Recommendations for Use of Retransformation Methods in Regression Models Used to Estimated Sediment Loads [“The Bias Correction Problem”]. Office of Surface Water Technical Memorandum No. 93.08. December 31. Vandenberghe, J., 2001. A typology of Pleistocene cold-based rivers. Quatern. Internl. 79, pp. 111-121. Walling, D.E. 1974. Suspended Sediment and Solute Yields from a Small Catchment Prior to Urbanization. Institute of British Geographers Special Publication No. 6: 169–192. Walling, D.E. 1977a. Limitations of the Rating Curve technique for Estimating Suspended Sediment Loads, with Particular Reference to British Rivers. In: Erosion and Solid Matter Transport in Inland Waters, Proceedings of Paris Symposium, July 1977. IAHS Publication No. 122: 34– 48. Walling, D.E. 1977b. Assessing the Accuracy of Suspended Sediment Rating Curves for a Small Basin. Water Resources Research, Vol. 13(3): 531–538.