Distributed hydrological modelling using weather radar in gauged and ungauged basins

Distributed hydrological modelling using space–time estimates of rainfall from weather radar provides a natural approach to area-wide flood forecasting and warning at any location, whether gauged or ungauged. However, radar estimates of rainfall may lack consistent, quantitative accuracy. Also, the formulation of hydrological models in distributed form may be problematic due to process complexity and scaling issues. Here, the aim is to first explore ways of improving radar rainfall accuracy through combination with raingauge network data via integrated multiquadric methods. When the resulting gridded rainfall estimates are employed as input to hydrological models, the simulated river flows show marked improvements when compared to using radar data alone. Secondly, simple forms of physical–conceptual distributed hydrological model are considered, capable of exploiting spatial datasets on topography and, where necessary, land-cover, soil and geology properties. The simplest Grid-to-Grid model uses only digital terrain data to delineate flow pathways and to control runoff production, the latter by invoking a probability-distributed relation linking terrain slope to soil absorption capacity. Model performance is assessed over nested river basins in northwest England, employing a lumped model as a reference. When the distributed model is used with the gridded radar-based rainfall estimators, it shows particular benefits for forecasting at ungauged locations.     

Influence of rock mass strength on the erosion rate of alpine cliffs

Collapse of cliff faces by rockfall is a primary mode of bedrock erosion in alpine environments and exerts a first‐order control on the morphologic development of these landscapes. In this work we investigate the influence of rock mass strength on the retreat rate of alpine cliffs. To quantify rockwall competence we employed the Slope Mass Rating (SMR) geomechanical strength index, a metric that combines numerous factors contributing to the strength of a rock mass. The magnitude of cliff retreat was calculated by estimating the volume of talus at the toe of each rockwall and projecting that material back on to the cliff face, while accounting for the loss of production area as talus buries the base of the wall. Selecting sites within basins swept clean by advancing Last Glacial Maximum (LGM) glaciers allowed us to estimate the time period over which talus accumulation occurred (i.e. the production time). Dividing the magnitude of normal cliff retreat by the production time, we calculated recession rates for each site. Our study area included a portion of the Sierra Nevada between Yosemite National Park and Lake Tahoe. Rockwall recession rates determined for 40 alpine cliffs in this region range from 0·02 to 1·22 mm/year, with an average value of 0·28 mm/year. We found good correlation between rockwall recession rate and SMR which is best characterized by an exponential decrease in erosion rate with increasing rock mass strength. Analysis of the individual components of the SMR reveals that joint orientation (with respect to the cliff face) is the most important parameter affecting the rockwall erosion rate. The complete SMR score, however, best synthesizes the lithologic variables that contribute to the strength and erodibility of these rock slopes. Our data reveal no strong independent correlations between rockwall retreat rate and topographic attributes such as elevation, aspect, or slope angle. Copyright © 2009 John Wiley & Sons, Ltd.     

Stream Temperature Modeling and Fiber Optic Temperature Sensing to Characterize Groundwater Discharge

The Ngongotaha Stream was used as a case study to assess the applicability of fiber optic distributed temperature sensing (FODTS) to identify the location of springs and quantify their discharge. Thirteen springs were identified, mostly located within a 115 m reach, five discharged from the right bank and eight from the left bank. To quantify groundwater discharge, a new approach was developed in which the one-dimensional transient heat transport model was fitted to the FODTS measurements, where the main calibration parameters of interest were the unknown spring discharges. The spatial disposition of the groundwater discharge estimation problem was constrained by two sources of information; first, the stream gains ∼500 L/s as determined by streamflow gauging. Second, the temperature profiles of the left and right banks provide the spatial disposition of springs and their relative discharges. FODTS was used to measure stream temperature near the left and right banks, which created two temperature datasets. A weighted average of the two datasets was then calculated, where the weights reflected the degree of mixing between the right and left banks downstream of a spring. The new approach in this study marks a departure from previous studies, in which the general approach was to use the steady-state thermal mixing model (Selker et al. 2006a; Westhoff et al. 2007; Briggs et al. 2012) to infer groundwater discharge, which is then used as an input into a transient model of the general form of equation to simulate stream temperature (Westhoff et al. 2007).     

Consequences of Groundwater-Model Vertical Discretization in Risk-Based Decision-Making

One of the first and most important decisions facing practitioners when constructing a numerical groundwater model is vertical discretization. Several factors will influence this decision, such as the conceptual model of the system and hydrostratigraphy, data availability, resulting computational burden, and the purpose of the modeling analysis. Using a coarse vertical discretization is an attractive option for practitioners because it reduces data requirements and model construction efforts, can increase model stability, and can reduce computational demand. However, using a coarse vertical discretization as a form of model simplification is not without consequence; this may give rise to unwanted side-effects such as biases in decision-relevant simulated outputs. Given its foundational role in the modeled representation of the aquifer system, herein we investigate how vertical discretization may affect decision-relevant simulated outputs using a paired complex-simple model analysis. A Bayesian framework and decision analysis approach are adopted. Two case studies are considered, one of a synthetic, linked unsaturated-zone/surface-water/groundwater hydrologic model and one of a real-world linked surface-water/groundwater hydrologic-nitrate transport model. With these models, we analyze decisions related to abstraction-induced changes in ecologically important streamflow characteristics and differences in groundwater and surface-water nitrate concentrations and mass loads following potential land-use change. We show that for some decision-relevant simulated outputs, coarse vertical discretization induces bias in important simulated outputs, and can lead to incorrect resource management action. For others, a coarse vertical discretization has little or no consequence for resource management decision-making.     

Automated co-registration and calibration in SfM photogrammetry for landslide change detection

Landslides represent hazardous phenomena, often with significant implications. Monitoring landslides with time-series surface observations can indicate surface failure. Unmanned aerial vehicles (UAVs) employing compact digital cameras, in conjunction with structure-from-motion (SfM) and multi-view stereo (MVS) image processing approaches, have become commonplace in the geoscience research community. These methods offer relatively low-cost, flexible solutions for many geomorphological monitoring applications. However, conventionally ground control points (GCPs) are required for registration purposes, the provision of which is often expensive, difficult or even impracticable in hazardous and inaccessible terrain. In an attempt to overcome the reliance on GCPs, this paper reports research that has developed a morphology-based strategy to co-register multi-temporal UAV-derived products. It applies the attribute of curvature in combination with the scale-invariant feature transform algorithm, to generate time-invariant curvature features, which serve as pseudo-GCPs. Openness, a surface morphological digital elevation model derivative, is applied to identify relatively stable ground regions from which pseudo-GCPs are selected. A sensitivity threshold quantifies the minimum detectable change alongside unresolved biases and misalignment errors. The approach is evaluated at two study sites in the UK, first at Sandford with artificially induced surface change, and second at an active landslide at Hollin Hill, with multi-epoch SfM-MVS products derived from a consumer-grade UAV. Elevation changes and annual displacement rates at dm-level are estimated, with optimal results achieved over winter periods. The morphology-based co-registration strategy resulted in relative error ratios (i.e. mean error divided by average flying height) in the range 1:800–2500, comparable with those reported by similar studies conducted with UAVs augmented with real time kinematic (RTK)-Global Navigation Satellite Systems. Analysis demonstrates the potential of the morphology-based strategy for a semi-automatic, and practical co-registration approach to quantify surface motion. This can ultimately complement geotechnical and geophysical investigations and support the understanding of landslide behaviour, model prediction and construction of measures for mitigating risks. © 2018 John Wiley & Sons, Ltd.     

Ram pressure stripping of spiral galaxies in clusters

We use three-dimensional SPH/ N -body simulations to study ram pressure stripping of gas from spiral galaxies orbiting in clusters. We find that the analytic expectation of Gunn & Gott, relating the gravitational restoring force provided by the disc to the ram pressure force, provides a good approximation to the radius at which gas will be stripped from a galaxy. However, at small radii it is also important to consider the potential provided by the bulge component. A spiral galaxy passing through the core of a rich cluster, such as Coma, will have its gaseous disc truncated to ∼4 kpc, thus losing ∼80 per cent of its diffuse gas mass. The time-scale for this to occur is a fraction of a crossing time ∼10⁷ yr. Galaxies orbiting within poorer clusters, or inclined to the direction of motion through the intracluster medium, will lose significantly less gas. We conclude that ram pressure alone is insufficient to account for the rapid and widespread truncation of star formation observed in cluster galaxies, or the morphological transformation of Sabs to S0s that is necessary to explain the Butcher–Oemler effect.     

Emerging Memorial Landscapes of Labor Conflict in the Cotton Textile South

While research into the formation of memorial landscapes in the American South has focused on those resulting from racial conflicts, a new landscape memorializing labor conflict and class consciousness is also emerging in the region's textile‐producing Piedmont. This memorialization poses significant challenges to dominant regional discourses of economic development and class mutuality in a region in which labor organizing and radical politics remain anathema. This paper examines this emerging landscape for what it can tell us about class relations in the region and the process by which memorial landscapes are formed.     

Pit lakes: their characteristics and the potential for their remediation

 Pit lakes form when open-pit mining operations are discontinued and dewatering ceases. The increase in open-pit metal mining since the 1970s will lead to the formation of numerous pit lakes over the next 50 years. Many of these lakes will develop acid sulfate conditions with high levels of dissolved metals. Approaches to remediation of these conditions that have been recommended include the addition of lime or other alkaline materials and the stimulation of sulfate-reducing bacteria. However, prevention rather than remediation is probably the preferable approach. Measures to prevent oxidation of mining waste and wall rocks, including measures to fill pits quickly with water, to inhibit the activity of acidophilic sulfur-oxidizing bacteria, and to promote anoxic conditions at the lake bottoms may minimize the formation of acids and dissolved metals. Received: 26 August 1999 · Accepted: 29 October 1999     

Recent bottom-current activity in the deep western Bay of Bengal

We present several types of data which show that strong geostrophic bottom currents are present in a broad valley in the deep western Bay of Bengal adjacent to the Indian margin. Sea-floor photographs show well-developed current lineations with scour marks on the northern sides and sediment deposition tails on the southern sides of some objects (such as fecal pellets) suggesting strong southward-flowing bottom currents. A direct current measurement made in the region confirms this inferred flow direction. The nepheloid layer is much stronger in the western Bay of Bengal than in any other region of the northern Indian Ocean and indicates strong turbulence and a high concentration of suspended sediment at or near the sea floor. Additional data which do not provide unequivocal evidence for, but may also be indicative of, the existence of the bottom currents are as follows: the dispersal of the peninsular Indian rivers-derived smectite-rich sediments all along the valley to as far as south of Sri Lanka; a zone of sediment waves (as recorded on 3.5-kHz echograms) parallel to the regional trend of bathymetric contours along the Indian margin; and the frequent occurrence of thin, sharp and uniform layers of fine sand and silt beds rather than thick graded turbidite beds in the cores from the broad valley in the deep western Bay of Bengal.