Canadian Landform Examples

The flat topography of the Red River Valley reflects the morphology of underlying bedrock covered with late Quaternary glacial and glaciolacustrine sediments. The meandering Red River occupies a shallow stream‐cut valley that became incised into the Red River Valley plain following the final recession of glacial Lake Agassiz. Extreme flows carried by the river overtop the sides of the stream‐cut valley and spread laterally up to several tens of kilometres across the plain. An array of flood protection infrastructure has been constructed in the landscape to mitigate the flood hazard.     

Monitoring the 1997 flood in the Red River Valley using hydrologic regimes and RADARSAT imagery

In this study, we attempt to relate hydrologic regimes of the 1997 flood in the Red River Valley to the areal extent of flooding, determined from RADARSAT imagery. We obtained ten scenes of RADARSAT imagery, from 27 April to 1 July, including bitmaps delineating flooded areas for each date, from the Manitoba Centre of Remote Sensing. These images were co-registered using an image-to-image registration process. By overlaying these flood maps in chronological order, we compared the areal extent of flooding with the hydrologic regimes of the Red River, expressed as relative depths of flooding above the bankful stage at selected gauging stations. The results of the study indicated that the area of flooding on 4 May (1,984 km ² ) corresponded well with the highest flood levels at several gauging stations. A previous scene on 27 April showed a larger area under water, but visual inspection of the processed imagery indicated a lack of conformity between flood level regimes and the areal extent of flooding on this date due to surface detention of pre-flood storm runoff. Thus, the RADARSAT imagery represented the flood regimes adequately only when its interpretations were combined with hydrologic analysis and visual inspection of surface characteristics of the floodplain.     

清代东太湖地区的湖田与水文生态

清代的东太湖地区的湖田出现了快速增长。随着山区水土流失,东太湖的泥沙量大增,水面植被也出现大扩展,淤积和湖田扩展也因此加速。在西部出现大缺口,大缺口在清代很快合拢。东部湖田发展使出太湖的水流受阻,吴淞江北移瓜泾口,进而使东北部湖田快速发展。湖田形成时往往先是大圩,后是小圩,以后逐步形成纵向交错的河网。植桑又加速了湖田水稻土的培肥,优良的水稻土在小圩规模上逐步形成。植桑养蚕与稻作的配合维持了传统江南生态农业的持续。     

Recent Hydrological Changes in the Avoca River Catchment,Victoria

Since the early 1970s the Avoca River catchment has experienced a marked increase in all discharges, particularly high magnitude ones. This results from a change in the rainfall/runoff relationship, which is probably due to rising groundwater tables. Since 1973 the frequency of flooding in the lower Avoca, Loddon and Avon-Richardson catchments has increased markedly, placing pressure on downstream flood mitigation and irrigation works, as well as contributing to the degradation of environmentally sensitive wetlands. It also has the potential to exacerbate rising groundwater/salinity problems of the lower catchments. Human interference and changes in the rainfall regime are assessed to explain the nature of the apparent change in streamflows of the Avoca River catchment.     

1世纪至20世纪中期上荆江流域河道与水环境变迁——基于荆江洪水位历史变迁的考察

清中叶以降,清宫档三汛(桃花汛、伏汛、秋汛)安澜奏本中所见荆江洪水位开始日益上涨,咸丰、同治年间,藕池、松滋决口向洞庭湖分流后,水势稍有缓解,至光绪年间复又急速抬升。不断上涨的洪水位对江北入江河流造成了两方面影响: 其一为河道的变迁,其二为水环境的变化。在沮漳河流域,涉及长江百里洲的变迁,沮漳河入江口的变动,长江主泓迁移,下百里洲靠岸及洲尾东摆引发沮漳河下游延长,以及山水、江水相互顶托造成水环境淤积。在玛瑙河流域,则表现为荆江洪水位抬升对河水的顶托现象,导致入江尾闾沼泽化。     

THE WATER BALANCE OF LAKE SEVAN BASED ON NEW DATA

Lake Sevan, the largest lake in the Caucasus, with an area of about 540 square miles, underwent a rapid drop of its water level after its discharge was artificially expanded in conjunction with the construction of a series of hydroelectric stations on the Razdan River, its outlet. The drop of the lake level was associated with adverse environmental consequences and led to a decision to transfer water from the nearby Arpa River to the lake to help maintain its level. The diversion tunnel from the Arpa River is under construction. New findings on the various components of the income and outgo of water have made it possible to adjust the water balance of Lake Sevan and to predict the balance after the Arpa-Sevan diversion tunnel goes into operation.     

Antarctic history: A reply to professor W. H. Hobbs

On July 25th 1983 a severe thunderstorm brought torrential rain and flooding to a small valley near Newcastleton in Roxburghshire. At one site within the valley, around 65 mm of rainfall was recorded in 75 minutes, though this was probably 2 km from the centre of the storm. The resulting peak flow was estimated at almost 170 m³s^‐1 from a drainage area of 36.9 km². Lightning killed some livestock whilst many more were drowned. The storm triggered peat slides on several hillsides and caused extensive erosion of river banks and damage to buildings and bridges. The associated high sediment load killed fish stocks in the receiving waters. The flood was a significant event in terms of its human disruption and its impact on the natural environment.     

Establishing Stage‐Discharge Relationships in Multiple‐Channelled,Ephemeral Rivers: a Case Study of the Diamantina River,Australia

The method for deriving a stage‐discharge relationship has a significant impact on the shape of the river's rating curve. We compare rating curves for a single gauging station on a mutiple‐channelled river in Australia compiled using three different methods – the Urban Runoff and Basin Systems (URBS) rainfall‐runoff model, an empirically‐based velocity‐area method, and the predictive Hydrologic Engineering Centre‐River Analysis System (HEC‐RAS) computer model. The rainfall‐runoff model was found to predict lower discharges for stage heights over 3.5 m than both the empirically‐based velocity‐area method and the HEC‐RAS model. The empirically‐based velocity‐area model predicts similar discharges to the rainfall‐runoff model for stage heights less than 3 m but much higher discharges for larger flood events. The HEC‐RAS model predicts higher discharges than both other rating curves at all stage heights probably due to under‐estimation of the impact of surface roughness on flow velocity. The three models are discussed with particular reference to their use on multiple‐channelled rivers.     

Palaeoenvironmental reconstruction at an oxbow lake situated at the lower Nottawasaga River,southern Ontario,Canada

Abstract

The purpose of this investigation at the lower Nottawasaga River in southern Ontario, Canada, was to reconstruct the impact of base level on fluvial stability and human occupation during the Holocene in a topographically confined section, where the river cuts through the Edenvale Moraine. Three cores were extracted from an oxbow lake (Doran Lake) and a ground-penetrating radar survey was executed in its vicinity to study wider subsurface alluvial architecture. Radiocarbon dating suggests that the Nottawasaga River became entrenched in the Edenvale Moraine early in the Holocene, with base-level lowering in the Lake Huron basin, and that Doran Lake formed towards the middle Holocene as a meander cutoff when water levels in the Lake Huron basin increased, leading to a period of fluvial instability, enhanced flow and floodplain aggradation. Fluctuating lake levels would have affected human settlement as well as the preservation and visibility of archaeological remains predominantly through vertical accretion.     

An Area‐Based Approach for Estimating Extreme Precipitation Probability

Accurate estimates of heavy rainfall probabilities reduce loss of life, property, and infrastructure failure resulting from flooding. NOAA's Atlas‐14 provides point‐based precipitation exceedance probability estimates for a range of durations and recurrence intervals. While it has been used as an engineering reference, Atlas‐14 does not provide direct estimates of areal rainfall totals which provide a better predictor of flooding that leads to infrastructure failure, and more relevant input for storm water or hydrologic modeling. This study produces heavy precipitation exceedance probability estimates based on basin‐level precipitation totals. We adapted a Generalized Extreme Value distribution to estimate Intensity‐Duration‐Frequency curves from annual maximum totals. The method exploits a high‐resolution precipitation data set and uses a bootstrapping approach to borrow spatially across homogeneous regions, substituting space in lieu of long‐time series. We compared area‐based estimates of 1‐, 2‐, and 4‐day annual maximum total probabilities against point‐based estimates at rain gauges within watersheds impacted by five recent extraordinary precipitation and flooding events. We found considerable differences between point‐based and area‐based estimates. It suggests that caveats are needed when using pointed‐based estimates to represent areal estimates as model inputs for the purpose of storm water management and flood risk assessment.     

近300年来新疆玛纳斯湖变迁研究

本文在充分分析、利用历史文献记载、精确解读历史地图信息的基础上,结合现代大比例尺地形图、遥感卫星影像资料,以及前人的科学研究和野外实地考察成果,运用历史地理逆向推演法,分析了近300年来玛纳斯湖的历史演化过程,确定了不同历史时期玛纳斯湖的地理位置,弥补了第四纪以来玛纳斯湖演化过程研究的空白,并且对不同历史时期区域自然因素与人文因素对玛纳斯湖流域水文变迁的影像进行了分析,为今后玛纳斯湖周围生态环境演化研究提出了新的研究重点和研究方向。     

Environmental response to land use at Lake Curlip,East Gippsland,Victoria

A palaeoecological approach was undertaken to investigate the last 400 years of change in vegetation, fire, nutrient mobility, lake productivity and erosion associated with Aboriginal and European land-use practices in a forested environment in eastern Victoria. Melaleuca ericifolia scrub, although present prior to European settlement, has expanded around Lake Curlip in the last 200 years, primarily due to the action of fire on a forest already weakened by drought. A fern understorey has declined in extent and a more open aspect has developed in the forest. Fire has been a major component of vegetation dynamics in the historical period. Erosion rates were comparatively low and associated with fire during prehistoric times, but after European settlement its increase is more closely related to land clearance and flooding than fire. The response of vegetation to both anthropogenic and natural influences changed during the historical period. Although fire is an integral part of vegetation change, it is not an over-riding effect at Lake Curlip. Drain construction in the swamp has reduced the impact that any accumulation of pasture improvement chemicals may have had on eutrophication of the lake.     

Storm Drains as Assemblages: The Political Ecology of Flood Risk in Post‐Colonial Bangalore

Cities around the world are increasingly prone to unequal flood risk. In this paper, I “materialize” the political ecology of urban flood risk by casting stormwater drains—a key artifact implicated in flooding—as recombinant socionatural assemblages. I examine the production of flood risk in the city of Bangalore, India, focusing on the city's informal outskirts where wetlands and circulations of global capital intermingle. Staging a conversation between Marxian and Deleuzian positions, I argue, first, that the dialectics of “flow” and “fixity” are useful in historicizing the relational politics of storm drains from the colonial to the neoliberal era. Second, flood risk has been heightened in the contemporary moment because of an intensified alignment between the flow/fixity of capital and storm drains. Storm drains—and the larger wetlands that they traverse—possess a force‐giving materiality that fuels urban capitalism's risky “becoming‐being”. This argument raises the need for supplementing political‐economic critiques of the city with sociomaterialist understandings of capitalism and risk in the post‐colonial city. The paper concludes with reflections on how assemblage thinking opens up a more distributed notion of agency and a more relational urban political ecology.     

‘Torrents of Terror’: the August 1998 Storm and the Magnitude,Frequency and Impact of Major Floods in the Illawarra Region of New South Wales

The Illawarra Region some 80 kilometres south of Sydney is characterised by a prominent coastal escarpment that rises to 700 m within 12 km of the coast and forms a locus for frequent, high intensity rainfall events. One of the most recent recorded events occurred on 17 August 1998 with rainfall intensities at several pluviometers exceeding 120 mm hr^‐1 over a duration of one hour, with up to 249 mm falling in 3.5 hours during the main storm burst. Detailed pluviometer data indicate that the storm was non‐stationary and moved down catchment producing a widespread zone of 120 mm hr^‐1 intensity rainfall over a 30 minute duration across mid‐lower catchment areas after similar intensity but longer duration rainfall in catchment headwaters. Slope‐area reconstructions of peak discharge indicate that small catchments on the escarpment within the zone of maximum intensity experienced close to 100% rainfall‐runoff relationships, with peak discharges correlated to short duration (<1 hr) peak rainfall intensities. Widespread erosion occurred particularly where urban development had encroached on natural water courses. Debris/hyperconcentrated flows originating from both anthropogenic and natural sediment sources caused damage to urban areas. This paper provides an overview of the spatial and temporal characteristics of the 17 August 1998 storm, the hydrologic and geomorphic response of the streams, and the nature of damage to urban areas. It reassesses the frequency of recent high‐magnitude rainfall/flood events in the region, discussing the relationships between rainfall intensities, estimates of flood magnitudes and stormwater channel capacities.     

Natural and unnatural complexities: flood control along Manitoba's Assiniboine River

Flooding and flood control long have been topics of concern for geographers and historians of North America, from Gilbert White's foundational work to attempts to understand the recent disaster in New Orleans. This paper considers the problem of flood control along the Assiniboine River in the province of Manitoba, Canada. The first section addresses the local landscape and the larger context, explaining changes in the relevant human and physical geography. The second section examines efforts to mitigate flooding, focusing on how the risk of inundation was shifted in location (not eliminated altogether) and compounded through time (not progressively resolved). The third focuses on a further source of complexity: the contested character of government jurisdiction. This final section also addresses major mid twentieth century changes in mitigation efforts: in the light of flooding on an unprecedented scale, governments became more open to compromise and more willing to undertake substantial projects. Gilbert White asserted that while floods are natural occurrences, flood damages are the responsibility of humanity. The question of responsibility might seem relatively clear in relation to flood mitigation, given that dykes are human constructions. The history of flood mitigation along the Assiniboine would suggest, however, that assigning responsibility for the failures and successes of flood mitigation is not so straightforward.     

Construction and Interpretation of a 60‐year Flow Record for the river Tay at Kenmore

The backward extension of a river flow record for the River Tay, based on daily water level observations from 1937–76, has created the third‐longest sensibly continuous daily flow record for any Scottish river based on direct observations. The paper describes the derivation of the record, and assesses the variability of the Tay discharge over the 60‐year period covered. Unprecedented winter, spring and flood flows in the late 1980s/1990s are reported, in the context of improving the understanding of hydroclimatic variability.     

铜瓦厢决口后黄河下游河道沿岸区域地形与河湖环境(1855-1911)

1855年黄河于铜瓦厢决口北徙,给下游沿岸区域地形与河湖环境造成很大影响。山东运河以西的平原地带距离决口处较近,泥沙淤积较多,地形抬高幅度明显,黄河在此区内漫流,扰乱了原有水系。汶、泗二河下游地带受黄河淤高河床的顶托,亦出现排水困难的局面,东平湖的形成与扩大即区内积水不断增多的结果。鲁中丘陵西侧平原地带,受黄河淤高河床的阻挡或黄水倒灌影响,长清至齐东各县境内的入黄河流均难以宣泄,直接促成新清河的开辟。徒马平原地带,受黄河决口改道影响,靠近黄河的徒骇河诸多支流被淤没,徒骇河则被黄水冲宽刷深,1907年黄河利津决口后,其尾闾河段亦被淤没。     

Fluid dynamics and fluid‐structural relationships in the Red Lake mine trend,Red Lake greenstone belt,Ontario, Canada

The Red Lake mine trend, a deformation zone in the Archean Red Lake greenstone belt that hosts the world‐class Campbell‐Red Lake gold deposit, is characterized by abundant foliation‐parallel iron‐carbonate ± quartz veins with banded colloform‐crustiform structures and cockade breccias overprinted by silicification and gold mineralization. There is an apparent incompatibility between the cavity‐fill structures of the veins and breccias (typically developed at shallow crustal depths) and the upper greenschist to lower amphibole facies metamorphic conditions recorded in the host rocks (indicating relatively deep environments). This, together with the development of veins along the foliation plane, represents an enigmatic problem that may be related to the interplay between fluid dynamics and stress field. We approach this problem through systematic study of fluid inclusion planes (FIPs) in the vein minerals, including the orientations of the FIPs and the pressure–temperature conditions inferred from fluid inclusion microthermometry. We find that fluid inclusions in the main stage vein minerals (pregold mineralization ankerite and quartz and syn‐ore quartz) are predominantly carbonic without a visible aqueous phase, whereas many inclusions in the postore stage contain an aqueous phase. Most FIPs are subvertical, and many are subparallel to the foliation. High fluid pressure coupled with the high wetting angles of the water‐poor, carbonic fluids may have been responsible for the abundance of brittle deformation features. The development of subvertical FIPs is interpreted to indicate episodic switching of the maximum principal compressive stress (σ₁) from subhorizontal (perpendicular to the foliation) to subvertical (parallel to the foliation) orientation. The subvertical σ₁ is favorable for the formation of foliation‐parallel veins, as fractures are preferentially opened along the foliation in such a stress regime, the origin of which may be linked to the fluid source.     

Sediment and solute transport in a representative basin

Suspended sediment and total dissolved material concentrations in stream flow were studied in Deep Creek Representative Basin near Cessnock, N.S.W. between April, 1976 and June, 1977. Sediment and solute transport rates were calculated at two gauging stations for individual flood events and low flow periods using the hourly hydrograph record, stage/season concentration-discharge relationships and calculated rating curves. Limitations in the use of the rating curve suggest that during flood hydrographs of long return period, calculated transport rates may be in error. A continuous record of concentration variation was sampled during one runoff event enabling comparisons to be made between methods of load calculation. For the satisfactory calculation of transport rates during extreme flood hydrographs, it is essential that concentration variation be accurately defined.     

Hydraulic Imperialism: Hydroelectric Development and Treaty 9 in the Abitibi Region

This study aims to untangle the knot of treaty-making, industrialization, and hydroelectric development in the Lake Abitibi region in northeastern Ontario by examining the extent to which industrialist discourses on waterways influenced changes to the physical and political landscape. An analysis of events leading up to the signing of Treaty No. 9 in 1906, and then the Abitibi River hydroelectric dams and concomitant flooding of Lake Abitibi in 1914–15 made possible by the treaty, is provided. Changes to Lake Abitibi during this period are evidence of a process of hydraulic imperialism whereby the Canadian state used waterways to exercise control of the James Bay watershed and encourage industrial and agricultural development in northeastern Ontario in the early twentieth century. This process not only contextualized the state’s understanding of Treaty No. 9 but is further evidence of inherent ambiguities concerning First Nations reserves around Lake Abitibi created by the treaty.