Olav Slaymaker

Landslide inventory in a rugged forested watershed: a comparison between air-photo and field survey data

Abstract Landslide inventories are routinely compiled by means of aerial photo interpretation (API). When examining photo pairs, the forest canopy (notably in old-growth forest) hides a population of “not visible” landslides. In the present study, we attempt to estimate how important is the contribution of landslides not detectable from aerial photographs to the global mass of sediment production from mass failures on forested terrain of the Capilano basin, coastal British Columbia. API was coupled with intensive fieldwork for identification and measurement of all landslides. A 30-year framework was adopted. We show that “not visible” landslides can represent up to 85% of the total number of failures and account for 30% of the volume of debris mobilised. Such percentages display high sub-basin variability with rates of sediment production varying by one order of magnitude between two sub-basins of the study area. This is explained qualitatively by GIS-based analysis of slope frequency distributions, drainage density, and spatial distribution of surficial materials. Such observations find further support in the definitions of transport-limited and supply-limited basins. As a practical consideration to land managers, we envisage that supplementary fieldwork for landslide identification is mandatory in transport-limited systems only. Fieldwork has demonstrated that gully-related failures have a greater importance than one could expect from API.

Hydrograph separation using stable isotopes, silica and electrical conductivity: an alpine example

Abstract Hydrograph separation of runoff events in two nested alpine/subalpine basins in the Coast Mountains of British Columbia was carried out using electrical conductivity, specific concentration of silica and the stable isotopes oxygen-18 and deuterium as hydrological tracers. The methods predicted consistent high pre-storm water contribution for the subalpine site (60–90%) but more variable contribution at the alpine basin outlet (25–90%). The pre-storm water contribution is much larger than had previously been expected. Precipitation is believed to run off as overland flow due to the steep slopes in combination with the hydrophobic soils until it can enter the subsurface environment. The rapid influx of stored water is possibly caused by pressure propagation in the macropore system which could be enhanced by the heavily fractured bedrock and permeable landslide debris acting as efficient hydrological conduits. The study suggests that alternative hydrological tracers such as electrical conductivity and silica concentration can be used under certain hydrological and lithological conditions. These alternative tracers should, however, be verified against more conventional tracers before use, as the behaviour depends on specific characteristics of each basin. At the upper basin outlet, both electrical conductivity (EC) and silica underestimated the pre-storm contribution. At the lower station, silica and EC showed a similar pattern to deuterium and oxygen-18 tracers. The calculated pre-storm component using EC was, however, 10–20% lower than the calculated values from the other three tracers. The advantage of using these alternative tracers is that hydrograph separation results can, a priori, be anticipated.

Mutual vulnerability, mutual dependence: The reflexive relation between human society and the environment.

Human society affects environmental change but is also vulnerable to these changes. This relation has generated a number of theories that either focus on how we affect the environment or how the environment affects us. Few theories explicitly focus on the interaction. This paper will establish the range of data required to give an assessment of how likely an ecosystem is to change (which we label environmental sensitivity) and the ability of communities to adapt (social resilience). These findings allow us to generate a new method for assessing the reflexive relation between society and the environment.

The sediment budget as conceptual framework and management tool

A review of the sediment budget concept, a brief history, cognate mass balances and the significance of the storage term. Questions of temporal and spatial scales, errors and uncertainties and the nature of system response. Management implications include natural hazards, climatic change and land use disturbance.

Geomorphology and global environmental change

Preface 1. Landscape, and landscape scale processes as the unfilled niche in the global environmental change debate: an introduction O. Slaymaker, T. Spencer and S. Dadson 2. Mountains O. Slaymaker and C. Embleton-Hamann 3. Lakes and lake catchments K. Kashiwaya, O. Slaymaker and M. Church 4. Rivers M. Church, T. P. Burt, V. J. Galay and G. M. Kondolf 5. Estuaries, coastal marshes, tidal flats and coastal dunes D. J. Reed, R. Davidson-Arnott and G. M. E. Perillo 6. Beaches, cliffs and deltas M. J. F. Stive, P. J. Cowell and R. J. Nicholls 7. Coral reefs P. Kench, C. Perry and T. Spencer 8. Tropical rainforests R. P. D. Walsh and W. H. Blake 9. Tropical savannas M. E. Meadows and D. S. G. Thomas 10. Deserts N. Lancaster 11. Mediterranean M. Sala 12. Temperate forests and rangelands R. C. Sidle and T. P. Burt 13. Tundra and permafrost dominated taiga M.-F. Andre and O. Anisimov 14. Ice sheets and ice caps D. Sugden 15. Landscape, landscape scale processes and global environmental change: synthesis and new agendas for the twenty-first century T. Spencer, O. Slaymaker and C. Embleton-Hamann Index.

Physiographically controlled allometry of specific sediment yield in the canadian cordillera: a lake sediment‐based approach

It is generally supposed that specific sediment yield declines as the drainage basin area increases, as part of the mobilized sediment becomes trapped in the downstream cascade of storage zones. In British Columbia, using fluvial suspended sediment load data, Church and Slaymaker (Nature 1989, Vol 337, pp. 452–454) have observed a pattern of increasing specific sediment yield at all spatial scales up to 3×104km2. This trend has been attributed to the dominance of secondary remobilization of Quaternary sediments over primary denudation of the land surface. Using a larger data set of lake sediment‐based estimates of long‐term sediment yield, sub‐regional patterns of specific yield have been investigated for the Canadian Cordillera. Between spatial scales of 0.9 and 190 km2 sediment yield trends are differentiated by physiography, as indicated by the variable allometry observed in the specific sediment yield–drainage basin area relations. Highest sediment yields were observed in the Coast Mountains where specific sediment yields conform to the regional pattern described by Church and Slaymaker. However, in flat‐lying plateau and major valley areas specific sediment yield decreases with increasing drainage area, thus conforming to the conventional model of sediment delivery. In several other sub‐regions of intermediate relief there were no significant relations between specific yield and drainage area. These results suggest that no single model of sediment yield is adequate to describe sediment transfer processes in the Canadian Cordillera at the sub‐regional scale.

Identification, characterization, and hydrological implications of water repellency in mountain soils, southern British Columbia

The physicochemical properties of soils, which determine how readily the soils wet, were shown to vary significantly in mountain soils collected at six sites in southern British Columbia, even within individual profiles. The results of water drop penetration time tests were used to classify samples using a very simple scheme which is based upon our current understanding of the possible physicochemical interactions between solid surfaces, water, and soil air. In all cases where the samples were collected at sites in the subalpine-alpine ecotone, a layer which either wets reluctantly or is water repellent exists at or near the surface of the profile. These layers occur only where there is evidence for accumulation of organic matter, and are usually no more than a few centimetres thick. At the one site which was below the alpine-subalpine ecotone, the soils wet readily throughout the profile. These results suggest that the type of organic matter which accumulates in soils of the alpine-subalpine ecotone of southern British Columbia either limits the affinity of soils for water or renders the soil water repellent. The relation between infiltration rate and ponding depth was explored experimentally for a set of soil samples from a site in which a repellent layer was developed to depths greater than thirty centimetres. It was found that the infiltration rate, which was less than 2.0 millimetres per day for all samples, was insensitive to changes in the ponding depth to a maximum applied depth of 400 millimetres, and that it remained approximately constant over time. These results suggest that water was transported primarily as a vapour rather than as a liquid. Given that water repellent soils are not uncommon in the alpine-subalpine ecotone of southern British Columbia, and that ponding depths on hillslopes would be several orders of magnitude less than those applied experimentally, it is inferred that transfer of water as a vapour within may be an important mechanism in such environments. In their interpretation of variable solute sources and hydrological pathways in a small subalpine basin in British Columbia, GALLIE & SLAYMAKER (1984) suggested that water repellency could account, in part, for the observed tendency of water to bypass the soil matrix. They noted that water repellency seemed to be preferentially associated with three of the six soil-vegetation complexes found in their field area. In explaining the relatively low solute yields from these same soils, GALLIE & SLAYMAKER (1985) inferred the importance of hydrophobicity in years when segregated soil ice did not form. Reasonable though these assumptions were, they were based on inference from scattered observations and BARRETTs Masters thesis (1981). No systematic analysis of the phenomenon of water repellency was undertaken. Water repellency appears to be associated with accumulation of certain types of organic compounds on mineral grains. BOZER, BRANDT & HEMWALL (1969) suggested that the molecules involved are probably amphophilic; that is, they have a polar end which is attracted to mineral surfaces, and a nonpolar end which is directed outwards to form a hydrophobic surface (fig.1). It has been documented that forest fires and slash burning may result in transformation, volatilization, and distribution of organic compounds to produce a repellent layer, which may revert to a non-repellent condition over a number of years (DEBANO, MANN & HAMILTON 1970, SAVAGE, OSBORNE, LETEY & HEATON 1972, REEDER & JURGENSON 1979, and GIOVANNINI & LUCCHESI 1983). Fungi and algae have been implicated in the production of water repellent soil (BOND & HARRIS 1964, SAVAGE, MARTIN & LETEY 1969, and MILLER & WILKINSON 1977), as have a variety of plant species, especially those native to semiarid environments. The vegetation implicated includes: Chaparral in California (KRAMMES & DEBANO 1965), Juniper in Utah (SCHOLL 1971) and Mallet trees in Australia (MCGHIE & POSNER 1980). As far as the authors are aware, there has been no previous documentation of water repellency as characteristic of soils in the alpine-subalpine ecotone of southern British Columbia. This paper begins with a discussion of the conceptual basis for characterization of the physicochemical properties of soils in general, and of water repellent soils in particular. The results of field studies of water repellent mountain soils at the site studied previously by GALLIE & SLAYMAKER (1984, 1985) and at other sites in southern British Columbia are presented. The paper closes with a summary of the results and conclusions. A subsequent paper will explore the implications of this phenomenon for overland flow and runoff generation (BARRETT & SLAYMAKER, in preparation).

The distinctive attributes of debris torrents

Abstract The term debris torrent was introduced in North Americas Pacific Northwest region to describe coarse-grained, rapid channelized flows rich in organic debris. Environmental conditions favouring their occurrence and distinctive criteria for recognition of debris torrents are discussed. A classification of gravitational and fluvial sediment transporting processes is presented as a framework for papers presented at the Debris Torrent Workshop 6a held in Vancouver in August, 1987.

Advances in Holocene mountain geomorphology inspired by sediment budget methodology

The sediment budget, which links sediment sources to sediment sinks with hydroclimatic and weathering processes mediating the response, is applied to the analysis of sediments in three alpine lakes in British Columbia. We provide two ways of using the sediment budget as an integrating device in the interpretation of mountain geomorphology. These approaches differ in their resolution and ability to budget the major components of the fine-sediment cascade in glaciated environments. Taken together, they provide an integrated index of landscape change over the Holocene. The first example compares the hydroclimatic controls of lake sedimentation for the last 600 years (A.D. 1370–1998) preserved in varved sediments from two of the lake basins. This hydroclimatological approach incorporates contemporary monitoring, air photo analysis, and detailed stratigraphy of sedimentation events within a single varve to infer the timing, sources, and preferred pathways of fine-grained sediments reaching the lake basins. The results indicate that glaciers, hillslope, and channel instability within the major subbasins are the principal sediment sources to the lake basins. Transitory sediment storage of glacially derived sediments within the channels is believed to modulate the episodic and more frequent delivery of sediments from adjacent hillslope and fluvial storage sites and direct routing of glacial rock flour during years of prolonged glacial melt. The second example, relying on the phosphorus geochemistry of sediments in an alpine lake basin, considers the evolution of phosphorus forms (from mineral to occluded and organic fractions) as a function of the soil development, inherent slope instability, and repeated cycles of glaciation and neoglaciation over the Holocene. This geochemical approach demonstrates that both neoglaciation and full glaciation have essentially zeroed the system in such a way that a high proportion of mineral phosphorus remains in the present lake sediments and the bioavailability of phosphorus (a key to ecosystem development) is low. Both examples illustrate the importance of variable sediment sources; the seasonality, frequency, and magnitude of sediment transfers; and the profound influence of ice cover over contemporary, neoglacial and Pleistocene time scales. They also signal the value of including both clastic and dissolved components in the sediment budget. D 2003 Elsevier Science B.V. All rights reserved.

Environmental reconstruction from a varve network in the southern Coast Mountains, British Columbia, Canada

Cores of annually laminated sediments (varves) from five lakes in the southern Coast Mountains of British Columbia, Canada, document clastic sediment response to climate and geomorphic change over the past 120 years. Interannual varve thickness correlates with annual flood magnitude. Interdecadal trends in varve thickness are influenced by other environmental factors such as glacier recession. Despite major differences in the lakes and their contributing watersheds, substantial concordance is observed among the records. A pronounced change in the nature of lake sedimentation, accompanied by higher interannual variability, occurred in 1980. The change coincides with an increase in the magnitude of autumn flooding and major re-organization of the North Pacific climate system. These results highlight new directions for palaeoenvironmental research using varved sediment records, specifically to study the magnitude and spatial extent of past hydro-climatic events.