Landslides Triggered by Typhoon Morakot in Taiwan

Landslides are general geomorphic erosion processes on hillslopes and can usually cause severe threats to human life and property due to their unexpected occurrence and fast traveling. Typhoon Morakot (in 2009) released more than 2000 mm rainfall during 6 days at the beginning of August 5 in Taiwan, leading to a large number of landslides, especially in southern Taiwan. Here we significantly devote this chapter to address the causes and effects of landslides in Cishan River watershed accompanied with the primary factors of landslide triggering such as the geologic and topographic settings and rainfall characteristics. We evaluate the devastation of landslides caused by Typhoon Morakot and its aftermath, and also assess the present status of landslide hazards mitigation strategies in Taiwan

Influence of Coastal Processes on Speleogenesis and Landforms in the Caribbean Region

Evolution of rocky coastlines is controlled by littoral, biological and fluvial processes. Resultant landforms are overprinted and/or new ones formed as a result of changes in sea level caused by glacioeustasy and/or local tectonics. On carbonate coasts, chemical erosion in the form of karstification takes on a dominant role. Type of karstification is an important factor in understanding carbonate coast evolution and landform development so it is critical to identify type of karstification. In this research, fractal indices were used to distinguish cave and thus karstification type. It was determined that fractal indices effectively differentiated cave types and the indices were used to distinguish cave types at study sites on Barbados, the ABC Islands (Aruba, Bonaire, Curaçao) and the Caribbean coast of the northeast Yucatan peninsula, Mexico. This research evaluated caves located in the phreatic, epiphreatic and vadose zones of the northeast coast of Quintana Roo, Mexico to determine the relationship between the caves and to coastal processes. Three distinct coastal landforms associated with caves on the study sites were evaluated to quantify and model the interplay of littoral, fluvial and karstic processes and cave and karst development. On Barbados, the combination of surface fluvial processes, and mixing-zone and fluvial-karstic dissolution, resulted in the formation of gullies. Some gullies contained caves in their bounding walls and/or served as points of recharge to fluvial caves. Bokas of the ABC islands are distinctive geomorphic structures that formed from the interplay of fluvial, littoral and mixing zone karstification. The morphology of the bokas was a function of dominant geomorphic process. The caletas of the Yucatan Caribbean were formed by karstification processes that also produced features with mixing-zone-like morphologies but with fluvio-karstic function. The results of this research expand the Carbonate Island Karst Model (CIKM), which explains eogenetic dissolutional processes and landforms on small carbonate islands, to one that includes carbonate islands of all sizes, and carbonate continental coasts

African river basins : their present geometry and recent past as a framework for their evolution

Includes bibliographical references (leaves 213-231).Fractals and scaling laws abound in nature, and it is said that geometry of river networks and basins is an epitome of this. This study investigates how on the tectonically unique African continent, scaling parameters, and in particular deviations from 'perfect fractal patterns' relate to parameters like underlying geology, climate, and vegetation through which the river flows. Stream and basin patterns are also used to reconstruct the past network geometry of rivers, and to shed some light on the drainage evolution of major African rivers

Ecological and geomorphological impacts of channel stability restoration in urban streams

Stream restoration projects that attempt to reduce channel incision and bank erosion by reconstructing the channel and grading and armoring stream banks (channel stability restoration projects) are common, particularly in urbanized watersheds. However, integrated assessment of changes in geomorphic processes and ecological properties within the channel and in the surrounding riparian zone induced by stability restoration has rarely been carried out across multiple restored streams. I provide such an assessment by measuring channel complexity, bed sediment dynamics, channel movement rates, riparian soil structure and function, and diatom communities in multiple restored streams located in urbanized watersheds and comparing these measurements to measurements from urban and forested reference streams. Stability restoration appears to have reduced lateral channel migration and channel incision through channel reshaping. Patterns of bed sediment movement were altered through the effects of added channel obstructions on flow dynamics and bed sediment size distribution. Channel stability restoration did not alter channel complexity, primarily because channel complexity was not reduced by urbanization as has commonly been assumed. Restoration did not alter diatom communities either, primarily because diatom communities responded more strongly to urbanization-induced changes in water chemistry. Riparian soils were negatively impacted by stability restoration, particularly compared to riparian buffer establishment, which had mostly neutral effects on riparian soils. Channel stability restoration can provide a minor increase in channel and bed sediment stability. However, changes in bed sediment stability were driven by in-channel restoration structures, which can be placed without grading the banks or reconstructing the channel. Riparian buffer restoration can also stabilize channels and will provide wood to channels, which can provide similar stabilization benefits as restoration structures. Restoration of channel stability using only in-channel structures and riparian vegetation planting would reduce the cost of stability restoration and reduce negative impacts to riparian soils. Even so, effects of stability restoration were often overwhelmed by processes operating beyond the channel boundaries, suggesting that reach-scale targeting of channel instability needs to be assessed at the watershed scale and may need to be given lower priority to such restoration approaches as stormwater management, which directly address the causes of channel instability

Rock avalanches in high mountains

A thesis submitted for the degree of Doctor of Philosophy of the University of LutonRock avalanches are a high magnitude, low frequency catastrophic mass movement involving the failure of over 1 x 106 m3 of mountainside. Rock avalanches are considered a major hazard of the high mountains due to the excessive run-out often associated with them. To date the mechanism that allows for such excessive travel distance is unproven although several dozen possibilities have been proposed. Rock-avalanche deposits exhibit characteristic features such as sharp lateral margins, confinement to local topography, super-elevation on valley sides, intensely fragmented interiors and preserved stratigraphy relative to the source. However, there are few detailed studies of the internal sedimentology of rock-avalanche deposits. Such studies are a vital piece of evidence in the search for the mechanisms of motion as rock avalanches are rarely witnessed. This thesis examines the detailed sedimentology of five rock avalanche deposits of varied lithology and morphology. A novel methodology is developed to sample deposits for their grainsize distributions (GSD). The GSD's prove similar for deposits, with significant variation due to preserved lithological banding in the interior. This finding refutes the commonly held view that rock-avalanche deposits are simply inversely graded. Instead, a facies model is developed of a coarse Carapace facies forming the surface and near surface that overlies a highly fragmented Body facies that is in turn underlain by the Basal facies that is free to interact with the substrate. The sedimentology of the Body facies is considered in fine detail and is shown to be fractal in nature, that is, self-similar at all scales of observation. A predictive sedimentological plot is presented that allows generation of the grain-size distribution and descriptive statistics from a simple estimation of weight percent gravel at a rock avalanche exposure. The morphology of rock-avalanche deposits are examined and a classification presented of 'spread' 'two-phase' and 'stalled'. The hazard and features of each morphology is described in relation to the observed deposits

Machine Learning Predicts Reach-Scale Channel Types From Coarse-Scale Geospatial Data in a Large River Basin

Hydrologic and geomorphic classifications have gained traction in response to the increasing need for basin-wide water resources management. Regardless of the selected classification scheme, an open scientific challenge is how to extend information from limited field sites to classify tens of thousands to millions of channel reaches across a basin. To address this spatial scaling challenge, this study leverages machine learning to predict reach-scale geomorphic channel types using publicly available geospatial data. A bottom-up machine learning approach selects the most accurate and stable model among∼20,000 combinations of 287 coarse geospatial predictors, preprocessing methods, and algorithms in a three-tiered framework to (i) define a tractable problem and reduce predictor noise, (ii) assess model performance in statistical learning, and (iii) assess model performance in prediction. This study also addresses key issues related to the design, interpretation, and diagnosis of machine learning models in hydrologic sciences. In an application to the Sacramento River basin (California, USA), the developed framework selects a Random Forest model to predict 10 channel types previously determined from 290 field surveys over 108,943 two hundred-meter reaches. Performance in statistical learning is reasonable with a 61% median cross-validation accuracy, a sixfold increase over the 10% accuracy of the baseline random model, and the predictions coherently capture the large-scale geomorphic organization of the landscape. Interestingly, in the study area, the persistent roughness of the topography partially controls channel types and the variation in the entropy-based predictive performance is explained by imperfect training information and scale mismatch between labels and predictors

A nested watershed study in the Kuparuk River basin, arctic Alaska: Streamflow, scaling, and drainage basin structure

Thesis (Ph.D.) University of Alaska Fairbanks, 1997The central hypothesis of this dissertation is that permafrost influences the form, function, and scaling of hydrologic and geomorphologic characteristics in the Kuparuk River basin in Northern Alaska. This problem was addressed using three approaches: field hydrologic studies, statistical scaling studies, and geomorphology studies using digital elevation models. Permafrost and snow exert significant controls on hydrologic processes in the Kuparuk River basin. Storm hydrographs show fast responses, long time lags, extended recessions, and high runoff/precipitation ratios. These features arise from the diminished storage capacity caused by permafrost. Summer storm flow compositions in the are dominated by old water, as is commonly observed in basins without permafrost. However, the thawing active layer imposes seasonal trends on storm flow composition and other streamflow characteristics. These seasonal trends are often masked by precipitation patterns. Significant differences exist in the spatial variability and scaling of streamflow between arctic and temperate basins. Streamflow in arctic basins is subject to simple scaling, whereas streamflow in temperate regions is subject to multiscaling. Since the variability of streamflow downstream results from the timing of storm hydrographs upstream, regional scaling differences may result from the differences in runoff generation mechanisms in basins with and without permafrost. Fractal analysis of channel networks, and the scaling of mass distribution suggest that channel networks in the Kuparuk River basin are underdeveloped. Hillslope water tracks convey water off slopes, but the organization of water tracks lacks universal characteristics of mass and energy distribution common to other rivers, and hence cannot be considered fluvial channels. However, the heads of water tracks are located where some theoretical models of channel initiation predict that channels should occur. A likely scenario is that a rudimentary channel network was formed soon after deglaciation, but was never allowed to develop into a mature network due to the limits that permafrost imposes on erosion. An encompassing conclusion is that the Kuparuk River basin is adjusted to arctic conditions in both form and function. Consequently, thermal changes to the existing permafrost condition may impose significant changes in the erosional development of channel networks and in the subsequent hydrologic response

GEOSPATIAL MODELLING OF PRAIRIE RIVERS: LINKING PHYSICAL INDICATORS OF FISH HABITAT TO LARGE SCALE GEOMORPHIC PATTERNS IN RIVER SYSTEMS USING GEOMORPHIC RESPONSE UNITS (GRU)

Rivers are inherently dynamic environments with fluctuations in water quality, hydrology, connectivity and geomorphology. Though geomorphology has long been recognized as an important driver defining biological, ecological, and physical habitat characteristics of rivers, a readily applied classification tool that links such characteristics has been lacking. The Geomorphic Response Unit (GRU) method provides a novel approach to identifying large scale patterns in geomorphic character that provide a link between the hydrological regime and different habitat types to which species respond. Specifically, I investigated whether Geomorphic Types and GRUs are related to the distribution and abundance of different fish species, reflecting unique physical habitat characteristics of individual GRUs. The thesis chapters are manuscript based. The second chapter identifies relationships between specific Geomorphic Types, identified using the Geomorphic Response Unit (GRU) methodology, and Lake Sturgeon overwintering locations in the South Saskatchewan and Saskatchewan Rivers. Habitat selection ratios suggest that Lake Sturgeon in the Upper South Saskatchewan River significantly selected for one of seven possible Types for overwintering. Logistic regression results found both Type 0 and Type 4 predicted significantly higher Sturgeon presence than all other Types (P = < 2e-16 for both). The third chapter examines relationships between GRUs and abundance of both mature and immature Carmine Shiner in the Birch River, Manitoba. Differences in the median mature Carmine Shiner CPUEs among the GRUs are not statistically different (Kruskal-Wallis test H =1.723; df = 3, p value = 0.632), though interesting qualitative relationships were identified which may inform further studies. The fourth chapter investigates whether GRUs derived using a large scale network approach are linked to the abundance of specific fish species in the Assiniboine River, Manitoba. A Kruskal-Wallis test identified significant differences in CPUE among GRUs for 10 of 14 tested species. Post-hoc pairwise multiple comparisons using Dunn’s Method with Bonferroni p-value correction for multiple paired tests isolated the GRUs that were different from one another. Overall, my findings suggest that Geomorphic Response Units (GRU) are an effective means of identifying patterns in geomorphic structure within Prairie Rivers at both reach and segment scales. Further, I identified links between both Geomorphic Types and GRUs and patterns in abundance of various fish species covering a wide range of life history traits. These findings suggest that GRUs have potential as a valuable fisheries habitat management tool, increasing efficiency of monitoring efforts through quantification of habitat availability, connectivity, and complexity in Prairie River systems

Analysis of land use changes and water resources in lowland catchments of Northern Germany

With increasing pressures from natural disturbances and anthropogenic activities, water quality is degraded and sustainable management becomes more challenging. A good understanding of the key influential factors for water resources will help to develop effective catchment management plans for addressing water resources issues. However, a systematic assessment of cause-effect relationships between land use and water quality or quantity is still rare, particularly across different temporal and spatial scales. This study aims to explore the spatially distributed catchment variables controlling landscape patterns, and to identify the important catchment characteristics and spatial scales for explaining the water quality or quantity dynamics. The rural lowland catchments (namely Kielstau and Stör) in Northern Germany were selected as study areas. Intensive field campaigns have been carried out in the two catchments: land use mapping in both catchments and a water quality campaign (2018-2019) in the Stör catchment that complements campaigns from 1992-1994 and 2009-2011. Different multivariate statistics and a hydrological modelling (SWAT) approach have been applied. The distribution patterns of each specific land use class were identified based on logistic regression analysis using spatially distributed variables. Furthermore, stepwise multiple linear regression (SMLR) and redundancy analyses (RA) were applied to investigate influences of main categories of catchment characteristics on water quality at multiple spatial and temporal scales. The SWAT model was calibrated and validated for modeling the dynamic processes of streamflow, sediment, total phosphorus (TP), and total nitrogen (TN). The variabilities in main water balance components and nutrients in response to varied landscape patterns were investigated by applying the integrated approach of SWAT modeling and partial least squares regression model (PLSR)