Using live vegetation volume to analyze the effects of plot Pinus massoniana Lamb on water and soil conservation under natural rainfall events

The 3-D spatial distributions of vegetation are of great significance for water and soil conservation but are rarely concerned in literatures. The live vegetation volume （LVV） was used to relate to water/soil loss under 144 natural erosive rainfall events from 2007 to 2010 in a typical water-eroded area of southern China. Quadratic polynomial regression models were established for five pure tree （Pinus massoniana Lamb） plots between LVV and water （rtmoff）/soil conservation effects （RE/SE）. RE/SE corresponds to the ratios of runoff depth/soil loss of the pure tree plots to that of the control plot under each rainfall event. Increasing LVV exhibits descending （DS）, descending-ascending （DA）, ascending-descending （AD）, and ascending （AS） trends in the LVV-RE and LVV-SE curves. The effects of soil conservation on the plots were generally more noticeable than the effects of water conservation, and most of the RE and SE values reflected the positive effects of water and soil conservation. The effects were mainly positive under heavy rains （e.g., rainfall erosivity, R = 140 MJ mm ha-l h, maximum 30 min intensity, I30 = 16 mm h-l）, whereas the effects were mainly negative under light rains （e.g., R = 45 MJ mm ha-1 h, I30 = 8 mm h-l）. The trees＇ water/soil conservation effects notably transformed when rainfall erosivity and intensity were lower than the positive or negative effects to a certain threshold. About 50% rainfall events led to obvious transform effects when LVVs were near 0.5 or 0.6. These results are able to aid in the decision making on the forest reconstruction in water-eroded areas.     

Modelling soil erosion in tropical environments using remote sensing and geographical information systems

Abstract

Soil erosion probability maps were produced under various case scenarios by accounting for uncertainties in the data and in the decision rule, using the Universal Soil Loss Equation (USLE), remote sensing and geographical information systems (GIS). This objective was realized by applying the Bayesian Probability Theory within IDRISI, a raster based GIS. The outcomes were two continuous probability soil erosion maps ranging from zero to 1. Comparing these maps with an earlier study indicates that accounting for the uncertainties has, in general, decreased the probability of soil erosion. Based on average readings for specific sites on the maps, increases in erosion risk under the second case scenario have had the highest impact on the highlands that is in the central, eastern, and northern regions of Langkawi Island, Malaysia. Assuming a 10% risk, this impact has increased by 11.98, 11.83 and 5.741% for high, medium and low soil erosion risk areas on the island respectively.     

Using neural networks for calibration of time-domain reflectometry measurements

Abstract

Time-domain reflectometry (TDR) is an electromagnetic technique for measurements of water and solute transport in soils. The relationship between the TDR-measured dielectric constant (K_a ) and bulk soil electrical conductivity ([sgrave]_a) to water content (θ_W) and solute concentration is difficult to describe physically due to the complex dielectric response of wet soil. This has led to the development of mostly empirical calibration models. In the present study, artificial neural networks (ANNs) are utilized for calculations of θ_w and soil solution electrical conductivity ([sgrave]_w) from TDR-measured K_a and [sgrave]_a in sand. The ANN model performance is compared to other existing models. The results show that the ANN performs consistently better than all other models, suggesting the suitability of ANNs for accurate TDR calibrations.     

Estimation of temporal variation of sediment yield using GIS / Estimation de la variation temporelle de l'exportation sédimentaire grâce à un SIG

Abstract

A GIS-based method is proposed for computation of temporal variation of sediment yield during isolated storm events. Data from three Indian catchments, namely Karso and Nagwa in Jharkhand and Kharkari in Rajasthan, have been used. The Integrated Land and Water Information System (ILWIS) GIS package was used for (a) catchment discretization into cell areas using grid networks, (b) evaluation of the spatial variation in catchment topographical characteristics and land use, and (c) presentation of the results obtained. The process of sediment delivery from grid cells to the catchment outlet is represented by the topographical characteristics of the cells. Unit sediment graphs for the catchments are derived by translation of the sediment yield from the grid cells and routing through a linear storage reservoir. The proposed method is found to provide satisfactory estimates of the temporal variation of sediment yield during isolated storm events. The total sediment yield of a storm event may also be computed using the proposed method.     

Temporal dynamics of soil water balance components in a karst range in southeastern Spain: estimation of potential recharge

Abstract

This paper analyses the temporal dynamics of soil water balance components in a representative recharge area of the Sierra de Gádor (Almeria, southeastern Spain) in two hydrological years. Two approaches are used to estimate daily potential recharge (PR): Approach 1 based on deriving PR from the water balance as the difference between measurements of rainfall (P) and actual evapotranspiration (E) obtained by eddy covariance; and Approach 2 with PR obtained from the dynamic pattern of the soil moisture (θ) recorded at two depths in the site's thin soil (average 0.35 m thickess). For the hydrological year 2003/04, which was slightly drier than the 30-year average, E accounted for 64% of rainfall and occurred mainly in late spring and early summer. The PR estimated by Approach 1 was 181 ± 18 mm year^-1 (36% of rainfall), suggesting an effective groundwater recharge in the study area. In the unusually dry hydrological year 2004/05, E was about 215 mm year^-1, close to the annual rainfall input, and allowing very little (8 ± 12 mm year^-1) PR according to Approach 1. Estimation of PR based on Approach 2 resulted in PR rates lower than those found by Approach 1, because Approach 2 does not take into account the recharge that occurs through preferential flow pathways (cracks, joints and fissures) which were not monitored with the θ probes. Moreover, using Approach 2, the PR estimates differed widely depending on the time scale considered: with daily mean θ data, PR estimation was lower, especially in late spring, while θ data at 30 min resolution yielded a more reliable prediction of the fraction of total PR resulting from the downward movement of soil water by gravity.

Citation Cantón, Y., Villagarcía, L., Moro, M. J., Serrano-Ortíz, P., Were, A., Alcalá, F. J., Kowalski, A. S., Solé-Benet, A., Lázaro, R. & Domingo, F. (2010) Temporal dynamics of soil water balance components in a karst range in southeastern Spain: estimation of potential recharge. Hydrol. Sci. J. 55(5), 737–753.     

Determining short-term changes in the hydraulic properties of a sandy-loam soil by a three-run infiltration experiment

ABSTRACT

Soil structure-dependent parameters can vary rapidly as a consequence of perturbing events such as intense rainfall. Investigating their short-term changes is therefore essential to understand the general behaviour of a porous medium. The aim of this study is to gain insight into the effects of wetting, perturbation and recovery processes through different sequences of Beerkan infiltration experiments performed on a sandy-loam soil. Two different three-run infiltration experiments (LHL and LLL) were carried out by pouring water at low (L, non-perturbing) and high (H, perturbing) heights above the soil surface and at short time intervals (hours, days). The results demonstrate that the proposed method allows one to capture short-term variations in soil structure-dependent parameters. The developed methodology is expected to simplify the parameterization of hydrological models with temporally variable soil hydraulic properties.     

Inherent relationship of the USLE,RUSLE topographic factor algorithms and its impact on soil erosion modelling

ABSTRACT

The accurate representation of the Earth’s surface plays a vital role in soil erosion modelling. Topography is parameterized in the Universal Soil Loss Equation (USLE) and Revised USLE (RUSLE) by the topographic (LS) factor. For slope gradients of < 20%, soil loss values are similar for both models, but when the gradient is increased, RUSLE estimates are only half of those of USLE. The study aims to assess the validity of this statement for complex hillslope profiles. To that end, both models were applied at eight diverse mountainous sub-watersheds. The USLE and RUSLE indices were estimated utilizing the SEAGIS model and a European dataset, respectively. LS factors were in a 3:1 ratio (i.e. USLE:RUSLE) considering the entire basin area. For areas with slopes <20%, gross erosion estimates of both models converged. Sites of strong relief (>20%) USLE yielded significantly higher values than RUSLE.     

Predicting sediment transport by interrill overland flow on rough surfaces

Modelling soil erosion requires an equation for predicting the sediment transport capacity by interrill overland flow on rough surfaces. The conventional practice of partitioning total shear stress into grain and form shear stress and predicting transport capacity using grain shear stress lacks rigour and is prone to underestimation. This study therefore explores the possibility that inasmuch as surface roughness affects flow hydraulic variables which, in turn, determine transport capacity, there may be one or more hydraulic variables which capture the effect of surface roughness on transport capacity suffciently well for good predictions of transport capacity to be achieved from data on these variables alone. To investigate this possibility, regression analyses were performed on data from 1506 flume experiments in which discharge, slope, water temperature, rainfall intensity, and roughness size, shape and concentration were varied. The analyses reveal that 89·8 per cent of the variance in transport capacity can be accounted for by excess flow power and flow depth. Including roughness size and concentration in the regression improves that explained variance by only 3·5 per cent. Evidently, flow depth, when used in combination with excess flow power, largely captures the effect of surface roughness on transport capacity. This finding promises to simplify greatly the task of developing a general sediment equation for interrill overland flow on rough surfaces. Copyright © 1998 John Wiley & Sons, Ltd.     

Temporal variation in properties of an uncropped,ploughed Miamian soil in relation to seasonal erodibility

Knowledge of seasonal variation in soil structural and related properties is important for the determination of critical periods during which soil is susceptible to accelerated erosion and other degradative processes. The purpose of this research was to evaluate the magnitude of seasonal variations in selected soil and deposited sediment properties in relation to soil erodibility for a Miamian silt-loam soil (Typic Hapludalf) in central Ohio. Erosion plots (USLE-type) were established on a 4·5% slope and maintained under bare, ploughed conditions from 1988 to 1991. Particle size distribution, bulk density(ρ_b), percentage water stable aggregates (WSA), soil organic carbon (SOC), and total soil nitrogen (TSN) of both soil and sediment samples were monitored between Autumn 1989 and Spring 1991. The soil and sediment particle size distributions followed no clear seasonal trends. Soil ρ_b increased following tillage (1·20 Mg m⁻³) and was highest (1·45 Mg m⁻³) during the autumn owing to soil slumping and consolidation upon drying. Low winter and spring values of ρ_b and %WSA (20–50% lower than in autumn) were attributed to excessive wetness and freeze–thaw effects. Both SOC and soil TSN contents progressively declined (from 2·18 to 1·79% and 1·97 to 1·75 g kg⁻¹, respectively) after ploughing owing to maintenance of plots under bare, fallow conditions. Spring highs and autumn lows of sediment SOC (3·12 vs. 2·44%) and TSN (2·70 vs. 1·96 g kg⁻¹) contents were a result of the combined effects of soil microbial activity and rainfall erosivity. Soil properties such as bulk density, SOC and WSA, which vary seasonally, can potentially serve as predictors of seasonal soil erodibility, which, in turn, could improve the predictive capacity of soil erosion prediction models. © 1998 John Wiley & Sons, Ltd.     

Multi-scale permeability estimation for a tropical catchment

Physically based and spatially distributed modelling of catchment hydrology involves the estimation of block or whole-hillslope permeabilities. Invariably these estimates are derived by calibration against rainfall–runoff response. Rarely are these estimates rigorously compared with parameter measurements made at the small scale. This study uses a parametrically simple model, TOPMODEL, and an uncertainty framework to derive permeability at the catchment scale. The utility of expert knowledge of the internal catchment dynamics (i.e. extent of saturated area) in constraining parameter uncertainty is demonstrated. Model-derived estimates are then compared with core-based measurements of permeability appropriately up-scaled. The observed differences between the permeability estimates derived by the two methods might be attributed to the role of intermediate scale features (natural soil pipes). An alternative method of determining block permeabilities at the intermediate or hillslope scale is described. This method uses pulse-wave tests and explicitly incorporates the resultant effects of phenomena such as soil piping and kinematic wave migration. The study aims to highlight issues associated with parameterizing or validating distributed models, rather than to provide a definitive solution. The fact that the permeability distribution within the Borneo study catchment is comparatively simple, assists the comparisons. The field data were collected in terrain covered by equatorial rainforest. Combined field measurement and modelling programmes are rare within such environments. © 1998 John Wiley & Sons, Ltd.