Evaluating fine sediment mobilization and storage in a gravel‐bed river using controlled reservoir releases

Two controlled flow events were generated by releasing water from a reservoir into the Olewiger Bach, located near Trier, Germany. This controlled release of near bank‐full flows allowed an investigation of the fine sediment (<63 µm) mobilized from channel storage. Both a winter (November) and a summer (June) release event were generated, each having very different antecedent flow conditions. The characteristics of the release hydrographs and the associated sediment transport indicated a reverse hysteresis with more mass, but smaller grain sizes, moving on the falling limb. Fine sediment stored to a depth of 10 cm in the gravels decreased following the release events, indicating the dynamic nature and importance of channel‐stored sediments as source materials during high flow events. Sediment traps, filled with clean natural gravel, were buried in riffles before the release of the reservoir water and the total mass of fine sediment collected by the traps was measured following the events. Twice the mass of fine sediment was retained by the gravel traps compared with the natural gravels, which may be due to their altered porosity. Although the amount of fine sediment collected by the traps was not significantly related to measures of gravel structure, it was found to be significantly correlated to measures of local flow velocity and Froude number. A portion of the traps were fitted with lids to restrict surface exchange of water and sediment. These collected the highest amounts of event‐mobilized sediments, indicating that inter‐gravel lateral flows, not just surface infiltration of sediments, are important in replenishing and redistributing the channel‐stored fines. These findings regarding the magnitude and direction of fine sediment movement in gravel beds are significant in both a geomorphic and a biological context. Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of water quality on infiltration,runoff and interrill erosion processes during simulated rainfall

This paper discusses the effects of water quality on the hydrological and erosion response of non‐saline, non‐sodic soils during simulated rain experiments. It is well known that rain water quality affects the behaviour of saline soils. In particular, rain simulation experiments cannot be run using tap water if realistic values of infiltration rates and soil erosion are to be found. This paper reports on similar effects for non‐saline, non‐sodic soils. Two soils – a well‐aggregated clay‐rich soil developed on marine silty clay deposits and a soil developed on silt loam – were selected and subjected to a series of simulated rainstorms using demineralized water and tap water. The experiments were conducted in two different laboratories in order to obtain results independent of the tap water quality or the rainfall simulator characteristics. The results indicate that time‐to‐ponding is largely delayed by solute‐rich water (tap water). When tap water is used, infiltration rates are significantly overestimated, i.e. by more than 100 per cent. Interrill erosion rates increase by a factor of 2·5–3 when demineralized water is used. The silty clay soil was more affected by the water quality than the silt loam soil, with respect to infiltration and runoff production. Regarding interrill erosion rates, the two tested soils were similarly affected by the water quality. Therefore, it can be concluded that rainfall simulation experiments with non‐dispersive soils (e.g. non‐saline, non‐sodic) must also be conducted using water with very low electrical conductivity (i.e. less than 30–50 µS cm⁻¹), close to that of distilled water. The use of tap water certainly hampers comparisons and the relative ranking of the hydrological and erosion response of different soils, while parameter values, such as final infiltration rate or time‐to‐ponding, cannot be extrapolated and extended to natural situations. Therefore, the majority of hydrological and erosion models and parameter values measured during rainfall simulations in the past should be used with caution for all types of soils. Copyright © 2001 John Wiley & Sons, Ltd.     

城市固体废弃物填埋场表层土壤的降雨入渗规律研究

考虑到黄土地区气候特征和地下水的埋藏深度,城市固体废弃物填埋后,其淋洗液主要是以雨水入渗而产生,则上覆土层的厚度应该根据降雨入渗的深度而确定;根据土壤物理学和饱和-非饱和渗流理论,利用土体颗粒分析试验,求得土水特征曲线以及渗透曲线;通过有限元数值模拟,可得各种降雨条件下的水分入渗规律,为填埋场的顶层设计与淋洗液的溶质运移提供参考与依据。     

Infiltration in the Corgo River basin (northern Portugal): coupling water balances with rainfall—runoff regressions on a monthly basis

Abstract

A combination of water balances and rainfall—runoff regressions is used to calculate infiltration, overland flow, baseflow and change to the surface water reservoir, on a monthly basis; evapotranspiration from the underground reservoir, on an annual basis; and a lag phase of maximum infiltration and maximum baseflow within a hydrological year. The water balance equations are written for catchment areas formed on crystalline rocks and located in temperate climates. The regression lines are fitted to precipitations and river flows. In a first run, the model is tested with the Corgo River hydrographic basin, a small watershed in the Trás-os-Montes and Alto Douro province, northern Portugal. The results compare favourably with results of other groups, working under similar environmental conditions. The sensitivity of the model to changes in the basin characteristics and climate is tested by a second run using data from the Terva River basin, a nearby catchment that is much smaller than the Corgo basin and has a much lower effective precipitation, defined here as a difference between precipitation and potential evapotranspiration. As a consequence of having a lower effective precipitation, the river dry-out starts earlier in the Terva (May) than in the Corgo (June).     

Accuracy of the kinematic wave and diffusion wave approximations for time-independent flows with infiltration included

Errors in the kinematic wave and diffusion wave approximation for time-independent (or steady-state) cases of channel flow with infiltration were derived for three types of boundary conditions: zero flow at the upstream end, and critical flow depth and zero depth gradient at the downstream end. The diffusion wave approximation was found to be in excellent agreement with the dynamic wave approximation, with errors of less than 1·4% for KF²₀≥7·5, and up to 14% for KF²₀≤0·75 for the upstream boundary condition of zero discharge and finite depth, where K is the kinematic wave number and F₀ is the Froude number. The kinematic wave approximation was reasonably accurate except at the channel boundaries and for small values of KF²₀ (≤1). The accuracy of these approximations was significantly influenced by the downstream boundary, both in terms of the magnitude of the error and the segment of the channel reach for which these approximations would be applicable. © 1998 John Wiley & Sons, Ltd.     

Two universal runoff yield models: SCS vs.LCM

Runoff calculation is one of the key components in the hydrological modeling. For a certain spatial scale, runoff is a very complex nonlinear process. Currently, the runoff yield model in different hydrological models is not unique. The Chinese LCM model and the American SCS model describe runoff at the macroscopic scale, taking into account the relationship between total actual retention and total rainfall and having a certain similarity. In this study, by comparing the two runoff yield models using theoretical analyses and numerical simulations, we have found that: (1) the SCS model is a simple linear representation of the LCM model, and the LCM model reflects more significantly the nonlinearity of catchment runoff. (2) There are strict mathematical relationships between parameters (R, r) of the LCM model and between parameters (S) of the SCS model, respectively. Parameters (R, r) of the LCM can be determined using the research results of the SCS model parameters. (3) LCM model parameters (R, r) can be easily obtained by field experiments, while SCS parameters (S) are difficult to measure. Therefore, parameters (R, r) of the LCM model also can provide the foundation for the SCS model. (4) The SCS model has a linear relationship between the reciprocal of total actual retention and the reciprocal of total rainfall during runoff period. The one-order terms of a Taylor series expansion of the LCM model describe the same relationship, which is worth further study.     

Do biological soil crusts determine vegetation changes in sandy deserts? Implications for managing artificial vegetation

Biological soil crusts (BSCs), which are widespread in arid and semiarid regions, such as sandy deserts, strongly influence terrestrial ecosystems. Once sand‐binding vegetation has been established on sand dunes, BSCs are colonized and gradually develop from cyanobacteria dominated crusts to lichen and moss dominated crusts on dune surfaces. We conducted this study to determine if the occurrence and development of BSCs in the Tengger Desert could be used to determine sand‐binding vegetation changes via altering soil moisture and water cycling using long‐term monitoring data and field experimental observation. BSCs changed the spatiotemporal pattern of soil moisture and re‐allocation by decreasing rainfall infiltration, increasing topsoil water‐holding capacity and altering evaporation. Changes in the soil moisture pattern induced shifting of sand‐binding vegetation from xerophytic shrub communities with higher coverage (35%) to complex communities dominated by shallow‐rooted herbaceous species with low shrub coverage (9%). These results imply that BSCs can be a major factor controlling floristic and structural changes in sand‐binding vegetation and suggest that the hydrological effects of BSCs must be considered when implementing large‐scale revegetation projects in sandy deserts. Copyright © 2010 John Wiley & Sons, Ltd.     

Seasonal mixing from intermittent flow drives concentration-discharge behaviour in a stream affected by coal mine drainage

Abandoned mining operations continue to severely degrade many ecosystems worldwide by releasing acidic water and/or heavy metals into surface and groundwater. Contaminant concentrations in affected streams vary with discharge in patterns that reflect both geochemical reactions and variable mixing of contaminated and non-contaminated waters. However, controls on concentration-discharge (C-Q) patterns remain unclear, particularly for constituents that experience changing solubility across redox and pH gradients. Understanding the C-Q behaviour of contaminants aids in predicting both downstream transport and effects on aquatic life under variable flow. Here, we examined the C-Q behaviours of non-reactive (Na, K, Ca, Mg, Cl⁻) and reactive (Fe, Mn, Al, H⁺, SO₄²⁻) solutes in a stream contaminated with acid mine drainage in northeastern Ohio, USA. Concentration-discharge patterns at the watershed outlet primarily reflected mixing of contaminated baseflow with intermittent inputs of high pH water draining from a passive limestone treatment system into the stream. The treatment system acted as an ephemeral tributary that mitigated contamination in the stream by diluting solutes, raising pH, and driving metal precipitation, but only when flow was present during wet seasons. Consequently, AMD-derived reactive solutes (H⁺, Fe, Mn, Al) decreased with increasing stream discharge while relatively conservative solutes (e.g., Ca, Mg, K, Na) decreased only slightly or were chemostatic. This study highlights both the unique C-Q patterns of reactive solutes when compared to those of non-reactive solutes and the potential for intermittent streams to control C-Q behaviour in headwater catchments.     

Integrating observations and models to determine the effect of seasonally frozen ground on hydrologic partitioning in alpine hillslopes in the Colorado Rocky Mountains,USA

This study integrated spatially distributed field observations and soil thermal models to constrain the impact of frozen ground on snowmelt partitioning and streamflow generation in an alpine catchment within the Niwot Ridge Long-Term Ecological Research site, Colorado, USA. The study area was comprised of two contrasting hillslopes with notable differences in topography, snow depth and plant community composition. Time-lapse electrical resistivity surveys and soil thermal models enabled extension of discrete soil moisture and temperature measurements to incorporate landscape variability at scales and depths not possible with point measurements alone. Specifically, heterogenous snowpack thickness (~0–4 m) and soil volumetric water content between hillslopes (~0.1–0.45) strongly influenced the depths of seasonal frost, and the antecedent soil moisture available to form pore ice prior to freezing. Variable frost depths and antecedent soil moisture conditions were expected to create a patchwork of differing snowmelt infiltration rates and flowpaths. However, spikes in soil temperature and volumetric water content, as well as decreases in subsurface electrical resistivity revealed snowmelt infiltration across both hillslopes that coincided with initial decreases in snow water equivalent and early increases in streamflow. Soil temperature, soil moisture and electrical resistivity data from both wet and dry hillslopes showed that initial increases in streamflow occurred prior to deep soil water flux. Temporal lags between snowmelt infiltration and deeper percolation suggested that the lateral movement of water through the unsaturated zone was an important driver of early streamflow generation. These findings provide the type of process-based information needed to bridge gaps in scale and populate physically based cryohydrologic models to investigate subsurface hydrology and biogeochemical transport in soils that freeze seasonally.     

降水入渗补给量随地下水埋深变化的实验研究

利用冉庄8m定埋深地中蒸渗仪的观测资料，根据蓄满产流理论，采用分层计算还原的方法，研究降水入渗补给量随地下水埋深的变化规律。揭示了最佳埋深和稳定点的形成机理。在试验条件下，最佳埋深出现在3m左右，降水入渗补给量随地下水埋深的增大而减小，6m以后趋于稳定。