River-ice effects on bank erosion along the middle segment of the Susitna river, Alaska

https://doi.org/10.1016/j.coldregions.2021.103239Get rights and content

Highlights

  • Bank erosion was driven or initiated by dynamic ice breakup.

  • Bank erosion rates varied by geomorphic reach.

  • Short term erosion rates are 3.5 to 8 times greater than long-term erosion rates.

  • Ice driven erosion on a gravel-bed river is episodic.

Abstract

This paper presents findings quantifying the extent to which river ice impacted and eroded banks along the middle segment of the Susitna River, Alaska. Analyses of aerial photography (taken over two, one-year periods) established bank-erosion rates for two reaches of differing morphology (multi-channel; and, single channel). Reconnaissance videos were used to establish the timing of erosion within each one-year period. Whereas the first winter ended with a thermal breakup of the river's ice cover, the second winter ended with the dynamic breakup of the ice cover in both reaches. The relatively low flow rate and weak ice associated with thermal breakup caused no large-scale erosion in the reaches, while the higher flow rates and stronger ice associated with dynamic breakup initiated large-scale bank erosion; up to 61% of bank erosion over a one-year period. Single year erosion values ranged from 10 to 30% of the historical erosion over two 30-yr periods. Analysis of the erosion and ice-scar data along the Middle River suggest the recurrence interval for dynamic ice-breakup is about 5–13 years. During dynamic breakup, ice-laden flows abraded banks, and directly impacted trees and shrubs. Thicker ice covers and ice jam development compounded ice-induced bank erosion in the multi-channel reach compared to the single channel reach.

Introduction

Observed effects of river ice on channel-bank erosion and channel alignment have been reported but few studies provide data on the extent that river ice erodes banks along river reaches. Descriptions exist of ice-run gouging and abrasion during ice-break up events (e.g., Marusenko, 1956; Smith, 1980; Beltaos, 1995; Zabilanksy et al., 2002; Prowse and J.M., 2003; Ettema and Kempema, 2012; Beltaos, 2018a; Beltaos et al., 2018; Baker et al., 2020). However, few studies have attempted to quantify the extent to which ice-related erosion of banks affects channel morphologies, such as bends (e.g., Ashton and Bredthauer, 1986). Osada et al. (2020), conversely, investigated how channel morphology affects ice conveyance, and found that morphology plays complex roles in this regard.

A broad question remains unanswered: Do river channels in boreal (subarctic) environments exhibit an ice-scoured morphology not explained by typical fluvial models? Several rivers in subarctic environments display channel morphologies typical of fluvial environments (Bray, 1982), other rivers have enlarged (widened) channels (e.g., Smith, 1979; Smith, 1980; Boucher, 2008; Boucher et al., 2009; Boucher et al., 2012). Many channels, though, exhibit equivocal effects of ice on channel morphology (e.g., Uunila and Church, 2015). Inherent in this broader question is defining the extent and frequency with which ice-induced processes cause bank erosion. The answers to these questions usually are specific to river reaches and watersheds (e.g., Best et al., 2005; Boucher, 2008).

To quantify the effects of ice on bank erosion, especially at the reach scale, is a complex undertaking, often complicated by the remoteness of river reaches in northern locations and the size of large rivers. The generation of datasets throughout the annual stages of river-ice, including ice formation, presence and breakup is typically costly and dangerous. However, an opportunity to quantify such erosion effects arose with the wide-ranging studies conducted of the Susitna River, Alaska, which was being considered as the site for a large hydroelectric project that included construction of a 215 m-high, hydroelectric dam (AEA, 2012). Baseline environmental studies were initially performed in the 1980s (Alaska Power Authority [APA], 1984) then more recently by the Alaska Energy Authority (AEA) in the period from 2011 to 2015. The studies produced an extensive, publicly available dataset regarding the behavior of the Susitna River during ice-covered and ice-free periods.

This paper presents the findings of a study that used the 2011–2015 dataset from the Susitna's Middle River segment (defined below) to quantify the extent to which bank erosion along the river is driven by river-ice or open-water fluvial processes. Though all the river's banks along the segment displayed signs of ice disturbance, the extent to which river ice influenced the alignment of the existing channel and drove bank erosion was unknown and unquantified. The study's objectives, therefore, include characterizing the ice processes causing the bank erosion, and quantifying when, annually, the majority of bank erosion occurs: during conditions of substantial open-water flow or, when ice floes and rubble are moving during the breakup of a channel's ice cover. The data suggest that negligible bank erosion occurs during ice-cover formation early in winter.

Section snippets

The Middle Susitna River and the study reaches

The Susitna River originates in the Alaska Range and is sub-divided into four large-scale geomorphic segments as it flows approximately 580 km to Cook Inlet near Anchorage, Alaska (Fig. 1). The river's most downstream, southerly geomorphic segments, including the Lower and Middle Rivers, do not flow through permafrost terrain. The Middle River extends 135 km downstream from the proposed dam site to the Susitna River confluence with two major tributaries (the Chulitna and Talkeetna Rivers) that

Investigation method

Two different reaches selected for investigation were monitored over two one-year periods, 2011–2012 and 2012–2013. The investigation comprised three parts:

  • 1.

    Observation of bank condition and erosion processes. On-the-ground bank observations between 2013 and 2014, and aerial-reconnaissance videos and photographs from 2011 through 2013 were analyzed to characterize dominant bank-erosion processes;

  • 2.

    Quantification of bank erosion. A time sequence of aerial photography was analyzed in GIS over two,

Results and discussion of erosion data

Erosion trends varied by study reach. The multi-channel reach (6), in comparison to the predominantly single channel reach (7), had an increased number of locations with lateral bank retreat (50 locations in Reach 6 compared to 13 locations in Reach 7 between 2012 and 2013), and an increased magnitude of total area eroded (5700 m2/km/yr in Reach 6 compared to 1400 m2/km/yr in Reach 7 between 2012 and 2013). Consistent with trends reported in the literature on ice jams (e.g., Beltaos, 1995), the

Conclusions

The two, one-year periods of observation along two reaches of the Middle Susitna River led to the following conclusions about the bank-erosion effects of river ice:

  • 1.

    Most bank erosion and consequent bank retreat occurred between 2012 and 2013, which was marked by the dynamic breakup of the river's ice cover. Minimal bank erosion and retreat occurred between 2011 and 2012, when the Middle River's ice cover disintegrated thermally.

  • 2.

    Over half of the erosion that occurred between 2012 and 2013, 61% of

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Acknowledgements

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Field data utilized as part of this study were collected as part of the Susitna-Watana Hydroelectric Project (FERC Project No. 14241) and funded by Alaska Energy Authority. All data are publicly available at the Susitna-Watana Hydroelectric GIS portal. The cumulative datasets, collected between 2011 and 2015 for each study, are posted at //gis.suhydro.org/reports/cumulative-suwa-data

References (67)

  • S. Beltaos et al.

    Field measurements of ice-jam-release surges

    Can. J. Civ. Eng.

    (2005)
  • H. Best et al.

    Association of ice and river channel morphology determined using ground-penetrating radar in the Kuparuk River, Alaska, Arctic

    Arct. Antarct. Alp. Res.

    (2005)
  • É. Boucher

    Analyse hydro-climatique et géomorphologique des déglacements mécaniques de la rivière Necopastic au Québec nordique

    (2008)
  • É. Boucher et al.

    Long-term and large-scale river-ice processes in cold-region watersheds

  • D.I. Bray

    Regime Equations for Gravel-Bed Rivers

  • M. Church et al.

    Discussion on processes and mechanisms of bank erosion

  • C.M. Collins

    Morphometric analyses of recent Channel changes on the Tanana River in the Vicinity of Fairbanks, Alaska. CRREL special Report 90-4

    (1990)
  • M. Donovan

    The Influence of Measurement Scale and Uncertainty on Interpretations of River Migration (Doctoral dssertation)

    (2019)
  • R. Ettema et al.

    River-Ice Effects on Gravel-Bed Channels

  • R. Gerard

    Hydroelectric Power Development and the Ice Regime of Inland Waters: A Northern Community Perspective. Surface Water Division National Hydrology Research Institute Environment Canada

    (1989)
  • G.E. Grant et al.

    A Geological Framework for Interpreting Downstream Effects of Dams on Rivers

  • A.M. Gurnell et al.

    Channel planform change on the river Dee meanders, 1876–1992

  • HDR Alaska, Inc

    2013 Ice Field Measurements. Appendix B to Initial Study Report, Part A: Sections 1-6, 8-10, Ice Processes in the Susitna River Study, Study Plan Section 7.6. Susitna-Watana Hydroelectric Project

    (2014)
  • HDR Alaska, Inc

    Detailed Ice Observations, October 2013 – May 2014. Ice Processes in the Susitna River, Study 7.6. Susitna-Watana Hydroelectric Project

    (2014)
  • HDR Alaska, Inc

    Initial Study Report, Part A: Sections 1-6, 8-10, Ice Processes in the Susitna River Study, Study Plan Section 7.6. Susitna-Watana Hydroelectric Project

    (2014)
  • HDR Alaska, Inc

    Initial Study Report, Part A: Sections 1-6, 8-10, Fish and Aquatics Instream Flow Study, Study Plan Section 8.5. Susitna-Watana Hydroelectric Project

    (2014)
  • D.J. Helm et al.

    Vegetation succession and disturbance on a boreal forest, Susitna River, Alaska

    (1997)
  • E.M. Kindle

    Notes on sedimentation in the Mackenzie River Basin

    J. Geol.

    (1918)
  • D.E. Lawson

    Erosion of perennially frozen streambanks. CRREL Special Report 83-29, U.S. Army Corps of Engineers

    (1983)
  • L.B. Leopold et al.

    River channel patterns: Braided meandering and straight

  • J.R. Mackay et al.

    The stability of ice-push features, Mackenzie River, Canada

    Can. J. Earth Sci.

    (1977)
  • Y.I. Marusenko

    The Action of Ice on River Banks

    Priroda

    (1956)
  • McNamara, J.P., Kane, D.L, 2009. The impact of a shrinking cryosphere on the form of arctic alluvial channels. Hydrol....
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