Lower Peace River Research Articles

The role of waves in ice‐jam flooding of the Peace‐Athabasca Delta

AbstractSince 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 Peace‐Athabasca Delta (PAD) region. To identify the causes of this trend, and to develop mitigation or adaptation strategies under present and future climatic conditions, it is necessary to understand the mechanisms that lead to breakup of the ice cover and jamming within the delta reach of Peace River. Because the lower Peace is extremely flat, the long‐period waves caused by spring snowmelt are not generally capable of dislodging the winter ice cover, even under conditions of very high flow. The ice cover decays in place and rubble generation, an essential condition for ice jamming, does not occur. However, major jams do, on occasion, form in the middle section of the river and make their way to the delta via repeated releases and stalls. Each release generates a steep wave which can greatly amplify the hydrodynamic forces that are applied on the ice cover and bring about its dislodgment. This is quantified for the lower Peace River by applying recently developed methodology to local hydrometric data. Detailed in situ observations in the spring of 2003, and additional data from 1997 and 2002, fully corroborate this conclusion. Implications to other flat rivers of northern Canada are discussed. Copyright © 2007 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Climatic effects on ice‐jam flooding of the Peace‐Athabasca Delta

AbstractThe 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. In recent decades, 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. Building on previous work that has identified the salient hydro‐climatic factors, the frequency of ice‐jam floods is considered under ‘present’ (1961–1990) and ‘future’ (2070–2099) climatic conditions. The latter are determined using temperature and precipitation output from the Canadian Climate Centre's second‐generation Global Climate Model (CGCM2) for two different greenhouse‐gas/sulphate emission scenarios. The analysis indicates that the ice season is likely to be reduced by 2–4 weeks, while future ice covers would be slightly thinner than they are at present. More importantly, a large part of the Peace River basin is expected to experience frequent and sustained mid‐winter thaws, leading to significant melt and depleted snowpacks in the spring. Using an empirical relationship between ice‐jam flood occurrence and size of the spring snowpack, a severe reduction in the frequency of ice‐jam flooding is predicted under both future‐climate scenarios that were considered. In turn, this trend is likely to accelerate the loss of aquatic habitat in the PAD region. Implications for potential mitigation and adaptation strategies are discussed. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Ice regime of the lower Peace River and ice‐jam flooding of the Peace‐Athabasca Delta

AbstractThe 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. Beginning in the mid‐1970s, 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 a habitat for aquatic life in the PAD region. Using archived hydrometric data and in situ observations, the ice regime of the lower Peace is described and quantified, setting the stage for identification of the conditions that lead to ice‐jam flooding and replenishment of Delta habitat. The first such condition is the occurrence of a mechanical, as opposed to a thermal, breakup event; second, the river flow should be at least 4000 m3/s; and third, an ice jam should form within the last 50 km of the Peace River. The type of breakup event depends on the freeze‐up stage and spring flow. The former has increased as a result of flow regulation, and the latter has decreased owing to changing climatic patterns. Both trends tend to inhibit the occurrence of mechanical breakups and contribute to less frequent ice‐jam flooding. Potential mitigation strategies are discussed. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Flood hydrology of the Peace‐Athabasca Delta, northern Canada

AbstractThis study conducted a systematic examination of the flood hydrology of the Peace‐Athabasca Delta (PAD), a complex and internationally important freshwater ecosystem located in northwestern Canada. Three distinct zones of floodwater origin within the PAD were discerned on the basis of the dominant hydrology and the topography represented by a digital‐elevation model (DEM): (1) perimeter Peace Delta, (2) perimeter Athabasca Delta, and (3) central delta lakes. Analysis of the satellite image and DEM‐derived flood maps of historically significant events, combined with field data of open‐water and ice‐influenced flood stages, revealed that ice‐jamming was the most effective and likely the only mechanism capable of recharging the highly elevated perimeter areas in the Athabasca and Peace Deltas. This supports the conclusion of previous studies that used hydrometric data external to the delta to infer inter‐delta flood conditions. By contrast, even the record open‐water flow to the Peace Delta could not generate overbank flow. Hydraulic simulation of the naturalized system (no dam & no weirs) suggests that overbanking of the lower Peace River would have been a rare occurrence without the effects of regulation. Both ice‐jam induced and open‐water high waters were found to recharge perched basins in the Athabasca Delta. Enlargement of the central delta lakes beyond the shoreline was determined to be an effective flood mechanism for filling low to mid‐elevation wetlands. Comparison of the observed and naturalized lake levels indicates that flow regulation of the Peace River and addition of the weirs on delta outflow channels has, depending on the year, led to an increase or a reduction in the annual maximum potential of inland flooding via lake expansion. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Numerical modelling of ice‐jam flooding on the Peace–Athabasca delta

AbstractIce jamming during the spring breakup of the ice cover in the lower reaches of the Peace River has been identified as the main agent of flooding and replenishment of the Peace–Athabasca delta (PAD) ecosystems. The relative rarity of major ice jams in the lower Peace River following construction of the Bennett Dam has resulted in serious habitat degradation and risk to local ecology, and concern has been raised over potential climate change impacts. This issue is under active study that encompasses use of various types of model, field data collection, and analysis of archived records. An important component of the study aims at determination of threshold flows that can result in significant flooding when a jam is in place in the PAD reach of the Peace. This question is investigated by means of RIVJAM, a numerical model that computes the water surface and thickness profiles of a jam in a given river reach. First, the model is calibrated using field data obtained during the 1996 and 1997 ice‐jam floods. Calibration coefficients are shown to be the same for both events and consistent with default values determined from previous applications in other rivers. A by‐product of the calibration process is the quantification of the flow reversals occurring under high‐stage conditions in the three major tributaries of the lower Peace. Next, the model is applied with increasing flow values and the resulting water surface profiles are compared with bank elevations. These comparisons indicate that an incoming flow of at least 4000 m3 s−1 is required to produce significant flooding of the delta. The calibrated model can also be used to examine the efficacy of controlled water releases at the Bennett Dam as a means of enhancing flooding potential. Copyright © 2003 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Regulation effects on the lower Peace River, Canada

AbstractThe headwaters of the Peace River, Canada became regulated in 1968 by a major hydroelectric facility and associated reservoir located in the Rocky Mountains. This paper examines the change to the downstream hydrographs that have resulted from regulation. To facilitate the comparison, a naturalized (without regulation effects) flow regime (1972–1996) was generated using a combination of hydrologic and hydraulic flow models. The results showed that even some 1100 km downstream, there have been significant changes to the hydrograph. Specifically, average winter flows were 250% higher, annual peaks (1‐day, 15‐day, 30‐day highs) were in the order of 35–39% lower, and overall variability in daily flows decreased. Despite the reduction in peaks and variability, however, the downstream hydrograph is far from flat and has retained the basic shape of the pre‐regulation hydrograph. This is primarily due to the strong influence of tributary inflow below the point of regulation. Recommendation for improvements to the model and future application of these data are also discussed. Copyright © 2001 John Wiley & Sons, Ltd.

Regulation effects on the lower Peace River, Canada

Regulation effects on the lower Peace River, Canada

Soil Properties of Boreal Riparian Plant Communities in Relation to Natural Succession and Clear-Cutting, Peace River Lowlands, Wood Buffalo National Park, Canada

Thirteen study sites on the floodplain and terraces ofthe lower Peace River, Wood Buffalo National Park,Canada, were examined for the effects of naturalforest succession and logging on physical and chemicalsoil properties. The principal changes in substratecharacteristics along the natural successional pathwaywere (i) development of a forest floor and (ii) burialof organic layers by floodwater deposition. Thephysical soil parameters of the forest floor andmineral soil were closely related to floodingfrequency, soil texture, stand closure, and forestfloor build-up. Significant differences in a number ofchemical soil properties between early (Barren Silt,Establishing) and late (Mature, Old-growth)successional stages were evident. The rising influenceof the developing plant community on chemical soilparameters was obvious. Organic carbon, totalnitrogen, cation exchange capacity, exchangeablecalcium, magnesium and potassium and extractablephosphorus level of forest floor and mineral soilswere highest in Mature sites; whereas pH and basesaturation were lowest. Physical and chemical soilproperties at three clear-cut sites were compared tosix undisturbed Mature/Old-growth stands. Removingvegetation had an effect on the physical soilproperties. A significant decrease in forest floornitrogen, cation exchange capacity, calcium andphosphorus occurred due to clear-cutting. Nosignificant change of chemical soil parameters wasobserved in the mineral soil at 0–20 cm depthfollowing harvesting. Significant impacts on chemicalsoil characteristics appeared to be limited to theforest floor. The absence of post-cutting sitepreparations makes the study area a useful benchmarkfor comparison with logged and scarified borealriparian sites elsewhere.

Pinus banksiana forests of the Fort Vermilion area, northern Alberta

Thirteen undisturbed Pinus banksiana Lamb. forests on Eutric Brunisols, derived from dune sands in the lower Peace River Valley, were analyzed quantitatively. Fort Vermilion has a dry, continental, subarctic macroclimate. Stands varied in age from 15 to 97 years, with tree volume increasing from 19 in younger to 193 m3 ha−1 in older stands. Cover of trees averaged 49%, shrubs 7%, dwarf shrubs 27%, forbs 6%, graminoids 1%, feather mosses 4%, caribou lichens 2%. Based on recurrently dominant species of well-developed vascular strata and growth-form guilds, a PINUS BANKSIANA/ROSA ACICULARIS/ARCTOSTAPHYLOS UVA-URSI – LATHYRUS OCHROLEUCUS community type is postulated for xeric sandhill habitats. This type is probably seral to a Picea glauca (Moench) Voss climax, but frequent fires prevent this. Plant succession during the sampled 80-year age interval is characterized by (i) increasing dwarf shrub, forb, and graminoid cover, (ii) stabilization of vascular species richness at ca. 35 species per stand, (iii) decline and stabilization of Simpson's dominance index, (iv) increasing Shannon–Weaver diversity, and (v) progressively gentler dominance–diversity slope angles. The niche preemption model (geometric series) of species structure fits younger and older better than middle-aged stands, based on goodness of fit of regression lines (r2) to dominance–diversity curves.

WHITE SPRUCE ROOTING MODIFICATIONS ON THE FLUVIAL DEPOSITS OF THE LOWER PEACE RIVER

Distinctive rooting modifications of white spruce were noted on fluvial sites of the lower Peace River. Photographs of these modifications are given and a multi-layered form is suggested to have arisen through adventitious rooting stimulated by periodic inundation. Significance of the modifications in silviculture is briefly discussed.