Prediction of overland flow and seepage zones associated with the interaction of multiple infiltration devices (cascading infiltration devices)

Infiltration devices are traditionally evaluated as standalone entities that do not interact with each other. A model is outlined that will allow interactions between proposed infiltration devices to be predicted prior to a development commencing. The model allows prediction of seepage into downslope devices and the assessment of the locations where the combined ground‐water mound will reach the surface and result in overland flow. The volume of overland flow discharged by the seepage zone may exceed the overland and piped flow received by the infiltration devices. Copyright © 2007 John Wiley & Sons, Ltd.     

Internal testing of a numerical model of hillslope–channel coupling using laboratory flume experiments

The numerical model COUP 2D simulates the hydrological coupling between hillslopes and the river channel during a rainfall event. In order to test the numerical model, a 1:100 scaled laboratory flume which was modified to incorporate lateral hillslope elements, was used to run a series of experiments in which hillslope angle, channel angle, hillslope discharge and channel discharge were the varying parameters. Overall, there were 18 different experimental configurations with three replicates carried out for each condition, leading to a total of 54 experiments. These conditions were then used to parameterize and run COUP 2D. Internal model outputs of flow depth and flow velocity at four cross‐sections in the channel were compared to the measurements made in the physical model for the same parameter conditions. Statistical comparisons of the measured and modelled data were carried out for each experiment and across all experiments, using two goodness‐of‐fit measures—root mean square error and Nash–Sutcliffe coefficient of efficiency—in order to assess the performance of the model over an entire simulation as well as over all the simulations. The main effects on the goodness‐of‐fit measures for flow depth of each experimental variable, as well as the interactions between variables, were evaluated using statistical modelling. The results show that the model captures flow‐depth variations in response to changing channel and hillslope parameters. Statistical modelling suggests that the main effects on model error are cross‐section position, channel angle and channel discharge. Significant interactions also occur between all the channel variables and between the channel variables and hillslope discharge. The results of the testing procedure have significant implications for the consideration of different model components and for the interaction between data‐ and model evaluation. Copyright © 2007 John Wiley & Sons, Ltd.     

Climate variability,snow, and physiographic controls on storm hydrographs in small forested basins,western Cascades,Oregon

Large floods are often attributed to the melting of snow during a rain event. This study tested how climate variability, snowpack presence, and basin physiography were related to storm hydrograph shape in three small (<1 km²) basins with old‐growth forest in western Oregon. Relationships between hydrograph characteristics and precipitation were tested for approximately 800 storms over a nearly 30‐year period. Analyses controlled for (1) snowpack presence/absence, (2) antecedent soil moisture, and (3) hillslope length and gradient. For small storms (<150 mm precipitation), controlling for precipitation, the presence of a snowpack on near‐saturated soil increased the threshold of precipitation before hydrograph rise, extended the start lag, centroid lag, and duration of storm hydrographs, and increased the peak discharge. The presence of a snowpack on near‐saturated soil sped up and steepened storm hydrographs in a basin with short steep slopes, but delayed storm hydrographs in basins with longer or more gentle slopes. Hydrographs of the largest events, which were extreme regional rain and rain‐on‐snow floods, were not sensitive to landform characteristics or snowpack presence/absence. Although the presence of a snowpack did not increase peak discharge in small, forested basins during large storms, it had contrasting effects on storm timing in small basins, potentially synchronizing small basin contributions to the larger basin hydrograph during large rain‐on‐snow events. By altering the relative timing of hydrographs, snowpack melting could produce extreme floods from precipitation events whose size is not extreme. Further work is needed to examine effects of canopy openings, snowpack, and climate warming on extreme rain‐on‐snow floods at the large basin scale. Copyright © 2008 John Wiley & Sons, Ltd.     

The impact of land use change and check‐dams on catchment sediment yield

Extensive land use changes have occurred in many areas of SE Spain as a result of reforestation and the abandonment of agricultural activities. Parallel to this the Spanish Administration spends large funds on hydrological control works to reduce erosion and sediment transport. However, it remains untested how these large land use changes affect the erosion processes at the catchment scale and if the hydrological control works efficiently reduce sediment export. A combination of field work, mapping and modelling was used to test the influence of land use scenarios with and without sediment control structures (check‐dams) on sediment yield at the catchment scale. The study catchment is located in SE Spain and suffered important land use changes, increasing the forest cover 3‐fold and decreasing the agricultural land 2·5‐fold from 1956 to 1997. In addition 58 check‐dams were constructed in the catchment in the 1970s accompanying reforestation works. The erosion model WATEM‐SEDEM was applied using six land use scenarios: land use in 1956, 1981 and 1997, each with and without check‐dams. Calibration of the model provided a model efficiency of 0·84 for absolute sediment yield. Model application showed that in a scenario without check dams, the land use changes between 1956 and 1997 caused a progressive decrease in sediment yield of 54%. In a scenario without land use changes but with check‐dams, about 77% of the sediment yield was retained behind the dams. Check‐dams can be efficient sediment control measures, but with a short‐lived effect. They have important side‐effects, such as inducing channel erosion downstream. While also having side‐effects, land use changes can have important long‐term effects on sediment yield. The application of either land use changes (i.e. reforestation) or check‐dams to control sediment yield depends on the objective of the management and the specific environmental conditions of each area. Copyright © 2008 John Wiley & Sons, Ltd.     

A new soil freeze/thaw discriminant algorithm using AMSR‐E passive microwave imagery

The soil freeze–thaw controls the hydrological and carbon cycling and thus affects water and energy exchanges at land surface. This article reported a newly developed algorithm for distinguishing the freeze/thaw status of surface soil. The algorithm was based on information from Advanced Microwave Scanning Radiometer Enhanced (AMSR‐E) which records brightness temperature (Tb) in the afternoon and after midnight. The criteria and discriminant functions were obtained from both radiometer observations and model simulations. First of all, the microwave radiation from freeze–thaw soil was examined by carrying out experimental measurements at 18·7 and 36·5 GHz using a Truck‐mounted Multi‐frequency Microwave Radiometer (TMMR) in the Heihe River of China. The experimental results showed that the soil moisture is a key component that differentiates the microwave radiation behaviours during the freeze–thaw process, and the differences in soil temperature and emissivity between frozen and thawed soils were found to be the most important criteria. Secondly, a combined model was developed to consider the impacts of complex ground surface conditions on the discrimination. The model simulations quite followed the trend of in situ observations with an overall relation coefficient (R) of approximately 0·88. Finally, the ratio of Tb18·7H (horizontally polarized Tb at 18·7 GHz) to Tb36·5V was considered primarily as the quasi‐emissivity, which is more reasonable and explicit in measuring the microwave radiation changes in soil freezing and thawing than the spectral gradient. By combining Tb36·5V to indicate the soil temperature variety, a Fisher linear discrimination analysis was used to establish the discriminant functions. After being corrected by TMMR measurements, the new discriminant algorithm had an overall accuracy of 86% when validated by 4‐cm soil temperature. The multi‐year discriminant results also provided a good agreement with the classification map of frozen ground in China. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of a river delta: a case study of Cimanuk river mouth,Indonesia

This paper describes delta development processes with particular reference to Cimanuk Delta in Indonesia. Cimanuk river delta, the most rapidly growing river delta in Indonesia, is located on the northern coast of Java Island. The delta is subject to ocean waves of less than 1 m height due to its position in the semi‐enclosed Java Sea in the Indonesian archipelago. The study has been carried out using a hydrodynamic model that accounts for sediment movement through the rivers and estuaries. As an advanced approach to management of river deltas, a numerical model, namely MIKE‐21, is used as a tool in the management of Cimanuk river delta. From calibration and verification of hydrodynamic model, it was found that the best value of bed roughness was 0·1 m. For the sediment‐transport model, the calibration parameters were adjusted to obtain the most satisfactory results of suspended sediment concentration and volume of deposition. By comparing the computed and observed data in the calibration, the best values of critical bed shear stress for deposition, critical bed shear stress for erosion and erosion coefficient were 0·05 N m^?2, 0·15 N m^?2, and 0·00001 kg m^?2 s^?1, respectively. The calibrated model was then used to analyse sensitivity of model parameters and to simulate delta development during the periods 1945–1963 and 1981–1997. It was found that the sensitive model parameters were bed shear stresses for deposition and erosion, while the important model inputs were river suspended sediment concentration, sediment characteristics and hydrodynamic. The model result showed reasonable agreement with the observed data. As evidenced by field data, the mathematical model proves that the Cimanuk river delta is a river‐dominated delta because of its protrusion pattern and very high sediment loads from the Cimanuk river. It was concluded that 86% of sediment load from the Cimanuk river was deposited in the Cimanuk delta. Copyright © 2008 John Wiley & Sons, Ltd.     

Arsenic as an indicator element for gold exploration in the region of the Xiangxi Au–Sb–W deposit, NW Hunan, PR China

The Xiangxi Au–Sb–W deposit, the largest of its type in northwestern Hunan, China, is a sulfide-dominated ore body hosted by low grade metamorphic red slates of the Neoproterozoic Madiyi Formation. Three stages of mineralization, quartz–scheelite, quartz–gold–pyrite, quartz–gold–stibnite, and one metal-barren stage of veining, quartz–calcite, are recognized. Arsenopyrite occurs only as a minor mineral phase in the second stage. Analyses for 21 trace elements show that the enrichment factors of As in the metal deposit (EC [=element concentration of sample/average content of an element in the upper crust]: 190; 43 samples) in ore veins and in the Guanzhuang and Yuershan reference sections (3.7 km and 2.7 km away from the Xiangxi mine, EC: 3.5; 96 samples) are much smaller than those of Sb (52855 [in ore veins], 117 [in the sections]), W (5665, 7.5) and Au (2727, 5.3). The background concentrations of Au and As in the two sections were 1.4 ppb and 1.4 ppm, respectively. Arsenic (with an anomaly coefficient [AC = number of anomalous samples/total number of samples] of 76%) forms a larger geochemical halo than W (AC: 8%) and Au (AC: 32%). Gold and As in the deposit were transported mainly as metal complexes such as Au(HS)⁻₂, H_nAs₃S⁻⁽³⁻ⁿ⁾₆ (n=1, 2 or 3) and HAsS⁰₂. Au(HS)⁻₂ is rapidly precipitated by a geochemical oxidation barrier — the red slates of the Madiyi Formation. As–S complexes in the stratigraphic horizon can be transformed into As–O complexes (e.g., H₃AsO⁰₃) under oxidizing conditions, and are continuously transported. Therefore, they can be widely distributed in the red slate units, thus forming extensive geochemical haloes, so that As can be used as an indicator element for Au exploration in the Xiangxi region.     

Nonlinear bacterial load‐streamflow response on a marine beach

Bacterial concentration (Escherichia coli) is used as the key indicator for marine beach water quality in Hong Kong. For beaches receiving streamflow from unsewered catchments, water quality is mainly affected by local nonpoint source pollution and is highly dependent on the bacterial load contributed from the catchment. As most of these catchments are ungauged, the bacterial load is generally unknown. In this study, streamflow and the associated bacterial load contributed from an unsewered catchment to a marine beach, Big Wave Bay, are simulated using a modelling approach. The physically based distributed hydrological model, MIKE‐SHE, and the empirical watershed water quality model (Hydrological Simulation Program – Fortran) are used to simulate streamflow and daily‐averaged E. coli concentration/load, respectively. The total daily derived loads predicted by the model during calibration (June–July 2007) and validation (July–October 2008) periods agree well with empirical validation data, with a percentage difference of 3 and 2%, respectively. The simulation results show a nonlinear relationship between E. coli load and rainfall/streamflow and reveal a source limiting nature of nonpoint source pollution. The derived load is further used as an independent variable in a multiple linear regression (MLR) model to predict daily beach water quality. When compared with the MLR models based solely on hydrometeorological input variables (e.g. rainfall and salinity), the new model based on bacterial load predicts much more realistic E. coli concentrations during rainstorms. Copyright © 2014 John Wiley & Sons, Ltd.     

Snow accumulation distribution inferred from time‐lapse photography and simple modelling

The spatial and temporal distribution of snow accumulation is complex and significantly influences the hydrological characteristics of mountain catchments. Many snow redistribution processes, such as avalanching, slushflow or wind drift, are controlled by topography, but their modelling remains challenging. In situ measurements of snow accumulation are laborious and generally have a coarse spatial or temporal resolution. In this respect, time‐lapse photography shows itself as a powerful tool for collecting information at relatively low cost and without the need for direct field access. In this paper, the snow accumulation distribution of an Alpine catchment is inferred by adjusting a simple snow accumulation model combined with a temperature index melt model to match the modelled melt‐out pattern evolution to the pattern monitored during an ablation season through terrestrial oblique photography. The comparison of the resulting end‐of‐winter snow water equivalent distribution with direct measurements shows that the achieved accuracy is comparable with that obtained with an inverse distance interpolation of the point measurements. On average over the ablation season, the observed melt‐out pattern can be reproduced correctly in 93% of the area visible from the fixed camera. The relations between inferred snow accumulation distribution and topographic variables indicate large scatter. However, a significant correlation with local slope is found and terrain curvature is detected as a factor limiting the maximal snow accumulation. Copyright © 2010 John Wiley & Sons, Ltd.     

Limiting equilibrium method for slope/drilled shaft system

The use of drilled shafts to stabilize an unstable slope has been a widely accepted practice. There are two basic design and analysis issues involved: one is to determine the global factor of safety of the drilled shafts stabilized slope and the other one is to determine the design earth thrust on the drilled shafts for structural design of the shafts. In this paper, a limiting equilibrium method of slices based solution for calculating global factor of safety (FS) of a slope with the presence of a row of drilled shafts is developed. The arching mechanisms due to the presence of the drilled shafts on slope were taken into account by a load transfer factor. The method for calculating the net force applied to the drilled shaft from the soil mass was also developed. The interrelationships among the drilled shaft location on the slope, the load transfer factor, and the global FS of the slope/shaft system were derived utilizing the developed numerical closed‐form solution. An illustrative example is presented to elucidate the use of the solution in optimizing the location of the drilled shafts on slope to achieve the desired global factor of safety of the slope/shaft system. Copyright © 2009 John Wiley & Sons, Ltd.