Frequency Of Ice-jam Flooding Research Articles

Coupling physical understanding and statistical modeling to estimate ice jam flood frequency in the northern Peace-Athabasca Delta under climate change

The Peace-Athabasca Delta (PAD) of northeastern Alberta is one of the largest inland freshwater deltas in the world, laying at the confluence of the Peace and Athabasca Rivers. The PAD is internationally recognized as having a unique ecological and cultural significance, and periodic ice jam flooding from both rivers is an important feature of its current ecology. Past studies have debated whether a change in ice jam flood frequency on the Peace River has recently occurred, and what factors might be driving any perceived changes. This study contributes to this debate by addressing two questions: (1) what factors are most predictive of large Peace River ice jam floods, and (2) how might climate change impact large ice jam flood frequency? This work starts with a physically-based conceptual model of the necessary conditions for a large Peace River ice jam flood, and the factors that indicate whether those conditions are met. Logistic regression is applied to the historical flood record to determine which combination of hydroclimatic and riverine factors best predict large ice jam floods and the uncertainty in those relationships given the available data. Climatic factors including winter precipitation and temperature are most predictive of large Peace River ice jam floods. Other factors including winter river flows and freeze-up elevation provide little additional predictive power. The best logistic regression model is then forced with downscaled climate change scenarios from multiple climate models to project large ice jam flood frequency for a variety of plausible futures. Parametric uncertainty in the best logistic regression model is propagated into the projections using a parametric bootstrap to sample many plausible statistical models. Although there is variability across emissions scenarios and climate models, all projections indicate that the frequency of large Peace River ice jam floods is likely to decrease substantially in the coming decades, and that average waiting times between future large ice jam floods will likely surpass recent experience.

Commentary on “Past variation in Lower Peace River ice-jam flood frequency” by Wolfe et al. (2020)

In contrast to a large body of scientific literature that is based on empirical data and physically based and mathematical analyses, Wolfe et al. (2020) cited proxy-based paleolimnological evidence and argued that the regulation of Peace River has not played a role in the reduced incidence of large ice-jam floods. Such events are essential to the sustenance of perched basins located in the Peace Sector of the Peace–Athabasca Delta. Herein, the arguments advanced by Wolfe et al. (2020) are critically examined and shown to be unconvincing. Relevant literature indicates that a drying trend was first noticed after construction of the Bennett Dam. It is shown, moreover, that the belatedly questioned Traditional Knowledge and Historical ice-jam flood record is a reliable source of information, at least with respect to large floods, which are crucial to perched-basin replenishment. Detailed examination of the Wolfe et al. (2020) magnetic susceptibility (MS) profiles and their interpretation points to serious inconsistencies and leads to a renewed recommendation for coring perched, rather than readily flooded, basins in the future. It is also recommended that the oxbow lakes cored nearly two decades ago be revisited to obtain updated MS profiles. Deficiencies in the interpretation of inferred isotopic-composition time series of three perched basins suggest that all factors influencing such environmental variables be considered before drawing conclusions regarding the frequency of past floods.

Response to Commentary by Beltaos and Peters on: “Past variation in Lower Peace River ice-jam flood frequency” by Wolfe et al. (2020)

Response to Commentary by Beltaos and Peters on: “Past variation in Lower Peace River ice-jam flood frequency” by Wolfe et al. (2020)

Multi-year isoscapes of lake water balances across a dynamic northern freshwater delta

Sustainable approaches capable of tracking status, trends and drivers of lake water balances in complex, remote landscapes are needed to inform ecosystem stewardship and water-security actions. At the Peace-Athabasca Delta (Alberta, Canada), a globally recognized freshwater floodplain landscape, concerns about water-level drawdown and multiple potential stressors have prompted need to improve knowledge of lake water balances and establish a lake monitoring program. Yet, the delta’s remoteness and dynamic nature present challenges to these goals. Here we use over 1000 measurements of water isotope composition at ∼60 lakes and 9 river sites during the spring, summer and fall of five consecutive years (2015–2019) to elucidate patterns in lake water balance over time and space, the influential roles of evaporation and river floodwaters, and relations with meteorological conditions and river water levels. Calculation of evaporation-to-inflow ratios using a coupled-isotope tracer approach, displayed via generalized additive models and geospatial ‘isoscapes’, reveal strongly varying lake water balances. Results identify distinct areas vulnerable to lake-level drawdown, given the likelihood of continued decline in ice-jam flood frequency, longer ice-free season duration and reduced snowmelt runoff. Results also demarcate areas of the delta where lakes are more resilient to factors that cause drawdown. The former defines the Peace sector, which is influenced by floodwaters from the Peace River during episodic ice-jam flood events, whereas the latter describes portions of the active floodplain environment of the Athabasca sector which receives more frequent contributions of Athabasca River floodwaters during both spring ice-jam and open-water seasons. Efficiency of water isotope tracers to capture the marked temporal and spatial heterogeneity in lake water balances during this 5 year time span, and their diagnostic responses to key hydrological processes, serves as a foundation for ongoing lake monitoring, an approach readily transferable to other remote and dynamic lake-rich landscapes.

Past variation in Lower Peace River ice-jam flood frequency

Opposing interpretations of Lower Peace River ice-jam flood frequency data sets are at the centre of identifying causes of reduced freshwater availability in the Peace-Athabasca Delta (northern Alberta), a Ramsar Wetland of International Importance and a major contributor to Wood Buffalo National Park’s listing as a UNESCO World Heritage Site. Recently, conclusions drawn from statistical inference of traditional knowledge and historical observation sources suggested that flood frequency was accelerating during 1880–1967 and then declined coincident with hydroelectric regulation of Peace River flow since 1968 that altered the river’s hydrograph. In contrast, prior paleolimnological measurements of laminated sediments from oxbow lakes proximal to the Peace River have, along with alternate presentation of the traditional knowledge and historical observation sources, identified flood frequency was in decline for decades preceding river regulation due to climate change since the Little Ice Age. Here we revisit these data sets and, specifically, review their inherent uncertainties to assess their value and limitations. The notion of increasing versus decreasing flood frequency in the decades preceding river regulation (1880–1967) is tested using previously published paleohydrological records from perched lakes in the delta. Those records from lakes most proximal and sensitive to changes in the flow regime of the Peace River show increasing influence of lake evaporation during 1880–1967, consistent with long-term decline in flood frequency. Reconciling uncertainties of multiple lines-of-evidence and their findings should inform decisions by UNESCO on the World Heritage status of Wood Buffalo National Park and execution of the park’s federally funded Action Plan. New paleolimnological studies that have recently been launched will continue to probe the hydrological history of the Peace-Athabasca Delta to serve as a foundation for effective stewardship.

Reply to discussions by Timoney et al. (2018) and Hall et al. (2018) on “Frequency of ice-jam flooding of Peace-Athabasca Delta”

The writer systematically refutes all of the discussers’ criticisms and supplies more details on the rigour of his “slope-based” frequency analysis. He also identifies key flaws of alternative and conflicting statistical interpretations proposed by the two discussion teams; and provides detailed documentation of the large uncertainty associated with paleolimnological assessments of ice-jam flood frequency.

Discussion of “Frequency of ice-jam flooding of Peace-Athabasca Delta”

Discussion of “Frequency of ice-jam flooding of Peace-Athabasca Delta”

Discussion of “Frequency of ice-jam flooding of Peace-Athabasca Delta”

Discussion of “Frequency of ice-jam flooding of Peace-Athabasca Delta”

“We Used to Say Rats Fell from the Sky After a Flood:” Temporary Recovery of Muskrat Following Ice Jams in the Peace-Athabasca Delta

Elders and Indigenous land users in the Peace-Athabasca Delta (PAD) have observed a dramatic decline in the relative abundance of muskrat in recent decades (~1935–2014). The main explanation for the decline has been reduction in suitable habitat as a result of decades with reduced frequency of ice-jam flooding on the Peace River. Under favourable conditions, ice jams can cause flooding of perched basins within the PAD that would otherwise receive no recharge from floodwaters. To examine whether abundance of muskrat in the PAD is driven by flooding, we tested the predictions that the density of muskrat (estimated by winter counts of houses) (1) was inversely related to the number of years since major ice jam floods and (2) increased with water depth. An ongoing collaborative monitoring program initiated in 2011, combined with analysis of data from past surveys (1973–2015), allowed Indigenous land users and scientists to document a 10 to 100-fold increase in the density of muskrat houses in 24 basins, over the two years following ice-jam flood events in the PAD. During 1973–2015, in the periods between major floods, density of houses dropped by approximately 79% for every year after a significant flood. In 27 basins surveyed from 2011 to 2015, density of muskrat houses increased by two orders of magnitude in the two years following a flood in the spring of 2014. Density of muskrat houses had a non-linear relationship with estimated depth of water at the time of fall freeze-up; the highest densities of muskrat houses were in basins with about 60 – 250 cm of water at the time of freeze-up. The depth of snow at the time of surveys did not have a strong relationship with the density of muskrat houses. However, few houses were counted in basins with more than 20 cm of snow, likely because deeper snow made it more difficult to conduct surveys and spot houses. Factors other than an increase in the depth of water at fall freeze-up may provide the mechanisms by which flooding affects muskrat. Density of muskrat houses is clearly tied to ice-jam flooding in the PAD. However, the local mechanisms by which floods affect muskrat are best understood by Indigenous land users and remain poorly understood by Western science. Indigenous peoples continue to regard muskrat as an indicator of ecological and cultural health of the PAD. This study highlights the value of consistent ecological monitoring that includes Indigenous knowledge.

Frequency of ice-jam flooding of Peace-Athabasca Delta

Major ice jams that occasionally form in lower Peace River generate extensive flooding, which helps replenish the perched basins of Peace-Athabasca Delta, a Ramsar wetland of international importance and a UNESCO World Heritage Site. This complex and dynamic ecosystem has experienced prolonged dry periods since the late 1960s, coincident with the construction of the W.A.C. Bennett hydroelectric dam in British Columbia. Physically-based and paleolimnological studies differ with respect to the impact of regulation on flood frequency. This issue is examined herein, based entirely on the historical record of observed ice-jam flood events.

Comparing the impacts of regulation and climate on ice-jam flooding of the Peace-Athabasca Delta

The Peace-Athabasca Delta (PAD) in northern Alberta is one of the world's largest inland freshwater deltas, home to large populations of waterfowl, muskrat, beaver, and free-ranging wood bison. Following construction of the Bennett Dam in the late 1960s, a paucity of ice-jam flooding in the lower Peace River has resulted in prolonged dry periods and considerable reduction in the area covered by lakes and ponds that provide habitat for aquatic life in the PAD region. Past studies have shown that both regulation and climate have contributed to the drying trend, via increased freezeup levels and reduced breakup flows, respectively. However, it has not so far been possible to assess the relative impacts of these two factors. This question is addressed herein by developing quantitative relationships based on the concept of conditional probability. The new methodology is first tested against observed frequencies of ice-jam floods both before and after regulation; it is subsequently applied to quantify the effects of climate and of regulation on the post-regulation reduction in ice-jam flood frequency. The results indicate that both factors have contributed significantly to the drying of the PAD, with regulation having had the more pronounced effect. Complications that may arise from secondary effects of regulation on breakup flows or of climate on freezeup levels are discussed and quantified. It is shown that such effects do not alter the overall conclusions of the paper.

Distributed function analysis of ice jam flood frequency

River ice jams can cause extreme flood events with major socio-economic and ecological impacts. A major practical question is how to quantify and assess ice-jam flood risk. Ideally, this question can be answered by means of historical ice-influenced water level peaks. More commonly, however, the available historical information is scarce and determination of ice-jam flood frequencies or probabilities must rely on a synthetic method. After noting that empirical evidence does not support the assumption of discrete stage outcomes, which is central to the existing methodology, a new synthetic method is developed. It hinges on the fact that the peak stage can take on any value between discharge-dependent envelopes and is thence called the distributed-function method, or DFM, and successfully tested by means of four case studies. It is shown further that the DFM produces more realistic results relative to those of the existing approach. Practical limitations are common to both methods and arise primarily from the need to use the peak runoff discharge, rather than the unknown value that prevails at the time of the peak stage. Resulting errors in probability estimates are evaluated in an extreme case and shown to be both conservative and tolerable. Analysis of additional case studies is recommended as a means of enhancing the utility of the DFM. ► Current methodology for synthetic stage-frequency analysis is examined. ► Inconsistencies relative to experience are noted and discussed. ► A distributed-function approach is developed as a preferred alternative. ► The new method is shown to perform well in four case studies. ► Practical limitations are quantified and future research is discussed.

Floodplain stratigraphy of the ice jam dominated middle Yukon River: a new approach to long‐term flood frequency

AbstractFloodplain stratigraphy is used as a new method for reconstructing ice jam flood histories of northern rivers. The method, based on reconstruction of the sedimentary record of vertically‐accreting floodplains, relies on stratigraphic logging and interpretation of floodplain sediments, which result from successive ice jam floods, and radiocarbon dating of inter‐flood organic material for chronology. In a case study along a reach of the Yukon River that straddles the Yukon–Alaska border, the method is used to develop a record of ice jam flooding for the last 2000 years. Detailed chronostratigraphic logs from three sites along the Yukon River indicates that the long‐term recurrence interval varies depending on location, but ranges from approximately once in 25 years to once in 38 years (or a probability of ca 3–4% in any given year). This is broadly similar to the 4·5% probability of recurrence calculated from archival and gauged data at Dawson City, Yukon Territory, for the period 1898–2006. Two of the three study locations, with sufficient chronology, suggest a decrease in flood frequency in the last several hundred years relative to the preceding period at each site, broadly corresponding to the Little Ice Age, suggesting climate exerts some control over long‐term ice jam flood frequency. This study demonstrates that the floodplain sedimentary record offers the potential to extend records of ice jam flooding in remote, ungauged northern rivers and provides a broader temporal context for assessing the frequency and variability of ice jam flooding. Copyright © 2008 John Wiley & Sons, Ltd.