Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Modelling the Influence of Groundwater Abstractions on the Water Level of Lake Naivasha, Kenya Under Data-Scare Conditions
Hogeboom, R.H.J. ; Oel, P.R. van; Krol, M. ; Booij, M.J. - \ 2015
Water Resources Management 29 (2015)12. - ISSN 0920-4741 - p. 4447 - 4463.
rift-valley - flow model - catchment - management - simulation - aquifer
This study presents the state-of-the-art understanding of the data-scarce and hydrogeologically complex groundwater system of Lake Naivasha, Kenya, with the particular aim of exploring the influence groundwater abstractions have on Lake Naivasha’s water level. We developed multiple alternative but plausible parameterizations for a MODFLOW groundwater model, based on literature, existing models and available data, while trying not to over-complicate the model. In doing so, we illustrate a possible strategy of going about data-scarce regions in modelling in general. Processes encountered in the calibrated parameterizations show groundwater flows laterally from the escarpments to the valley floor and axially from the lake along the Rift, with a larger portion flowing out southward than northward. Extraction of groundwater interrupts the flow from the northwestern highlands to the lake, leading to a lake stage reduction of 0.7–7.5 cm due to abstractions at our target farm (Flower Business Park) or an implied 7–75 cm due to total groundwater abstractions in the area. Although this study demonstrates our understanding of Naivasha’s groundwater system remains fragile and the current model cannot be embedded in operational water management yet, it (i) reflects the contemporary understanding of the local groundwater system, (ii) illustrates how to go about modelling in data-scarce environments and (iii) provides a means to assess focal areas for future data collection and model improvements.
Consequences of mixing assumptions for time-variable travel time distributions
Velde, Y. van der; Heidbüchel, I. ; Lyon, S.W. ; Nyberg, L. ; Rodhe, A. ; Bishop, K. ; Troch, P.A. - \ 2015
Hydrological Processes 29 (2015)16. - ISSN 0885-6087 - p. 3460 - 3474.
solute transport - stream chemistry - stable-isotopes - residence time - transit times - water storage - catchment - model - age - dispersion
The current generation of catchment travel time distribution (TTD) research, integrating nearly three decades of work since publication of Water's Journey from Rain to Stream, seeks to represent the full distribution in catchment travel times and its temporal variability. Here, we compare conceptualizations of increasing complexity with regards to mixing of water storages and evaluate how these assumptions influence time-variable TTD estimates for two catchments with contrasting climates: the Gårdsjön catchment in Sweden and the Marshall Gulch catchment in Arizona, USA. Our results highlight that, as long as catchment TTDs cannot be measured directly but need to be inferred from input-output signals of catchments, the inferred catchment TTDs depend strongly on the underlying assumptions of mixing within a catchment. Furthermore, we found that the conceptualization of the evapotranspiration flux strongly influences the inferred travel times of stream discharge. For the wet and forested Gårdsjön catchment in Sweden, we inferred that evapotranspiration most likely resembles a completely mixed sample of the water stored in the catchment; however, for the drier Marshall Gulch catchment in Arizona, evapotranspiration predominantly contained the younger water stored in the catchment. For the Marshall Gulch catchment, this higher probability for young water in evapotranspiration resulted in older water in the stream compared to travel times inferred with assumptions of complete mixing. New observations that focus on the TTD of the evapotranspiration flux and the actual travel time of water through a catchment are necessary to improve identification of mixing and consequently travel times of stream water. Copyright © 2014 John Wiley & Sons, Ltd.
Changes in agricultural land use affecting future soil redistribution patterns: A case study in southern tuscany (ITALY)
Debolini, M. ; Schoorl, J.M. ; Temme, A.J.A.M. ; Galli, M. ; Bonari, E. - \ 2015
Land Degradation and Development 26 (2015)6. - ISSN 1085-3278 - p. 574 - 586.
ne spain - landscape evolution - driving forces - sediment yield - erosion - model - management - region - abandonment - catchment
Land-use changes (LUCs) can be defined as the result of the direct action of the stakeholders in a particular area and natural or human driving forces. LUCs can influence various processes within the landscape and can have an impact on landscape functions. An analysis of the impact of LUCs on landscape processes can help to focus future rural policies. LUCs in Mediterranean areas particularly affect landscape functions because of their agro-pedoclimatical characteristics. The aims of this work are as follows: (i) to characterise LUCs in the last 11¿years in a typical Mediterranean area, the Trasubbie river basin (southern Tuscany, Italy); (ii) to extrapolate these changes and create spatially explicit LUC scenarios for the near future; and (iii) to simulate how and where the predicted LUCs may affect soil redistribution. We carried out an analysis of LUCs within the study area and used the trends to propose alternative scenarios for 2013. For these years, we spatially allocated land use (using the Conversions of Land Use and its Effects model) and used a landscape process model (landscape process modelling at multi-dimensions and scales) to assess soil redistribution patterns. Land use in the study area changed almost linearly between 1996 and 2007, with cereals and annual fodder crops decreasing, and vineyards, perennial pastures and land abandonment increasing. Our LUC scenario extrapolates these dynamics to make predictions for 2013. A comparison of LAPSUS results between LUC and baseline scenarios for 2013 showed an increase in terms of net soil loss and total erosion, and a decrease in terms of sediment delivery ratio.
Reconstruction of eroded and deposited sediment volumes of the embanked River Waal, the Netherlands, for the period AD 1631-present
Hobo, N. ; Makaske, A. ; Wallinga, J. ; Middelkoop, H. - \ 2014
Earth Surface Processes and Landforms 39 (2014)10. - ISSN 0197-9337 - p. 1301 - 1318.
rhine-meuse delta - floodplain sedimentation - budget - variability - management - catchment - storage - models - quartz - uk
In the last few centuries humans have modified rivers, and rivers have responded with noticeable changes in sedimentary dynamics. The objective of this study is to assess these responses of the sedimentary dynamics. Therefore, we calculated a sediment budget for eroded and deposited sediment volumes in a similar to 12-km long floodplain section of the largest semi-natural embanked but still dynamic lower Rhine distributary, for similar to 50-years time slices between AD 1631 and present. This is the period during which embanked floodplains were formed by downstream migration of meander bends between confining dykes. Our sediment budget involves a detailed reconstruction of vertical and lateral accretion rates and erosion rates of floodplain sediment. To do so, we developed a series of historical geomorphological maps, and lithogenetic cross-sections. Based on the maps and cross-sections, we divided the floodplain into building blocks representing channel bed and overbank sediment bodies. Chronostratigraphy within the blocks was estimated by interpretation of heavy metal profiles and from optically stimulated luminescence (OSL) dating results. Sediment budgets were hence calculated as a change of volume of each building block between time steps. The amount of lateral accretion initially increased, as a result of island and sand bar formation following embankment. From the eighteenth century onwards, there was a decrease of lateral processes in time, which is a result of straightening of the river by human activities, and a reduction of water and sediment supply due to the construction of a new upstream bifurcation. With straightening of the river, the floodplain area grew. Artificial fixation of the channel banks after AD 1872 prevented lateral activity. From then on, overbank deposition became the main process, leading to a continuous increase of floodplain elevation, and inherent decrease of flooding frequency and sediment accumulation rate.
Hydrological services and the role of forests: Conceptualization and indicator-based analysis with an illustration at a regional scale
Carvalho-Santos, C. ; Honrado, J.P. ; Hein, L.G. - \ 2014
Ecological Complexity 20 (2014). - ISSN 1476-945X - p. 69 - 80.
amplifies flood risk - ecosystem services - water yield - vegetation changes - developing-world - global evidence - land-use - catchment - erosion - afforestation
Forests are among the most important ecosystems for the provision of hydrological services. These include water supply and water damage mitigation, in the dimensions of quantity, timing and quality. Although the hydrological role of forests is well documented in the literature, a conceptual framework integrating these three dimensions is still missing. In this study, a comprehensive conceptual framework to improve the assessment of hydrological services provided by forests was developed. In addition, the framework was tested by an illustration for northern Portugal, a region with both Mediterranean and Atlantic climatic influences. The TEEB (The Economics of Ecosystems and Biodiversity) framework of ecosystem services was adapted to the relation between forests and water. Then, this new framework was complemented with a set of spatially-explicit indicators that quantify the supply and demand of hydrological services. In addition, the implications of the framework were discussed in the context of the social-ecological systems, using the DPSIR (Drivers, Pressures, State, Impacts, and Responses) model. Finally, the framework and the indicators were illustrated for northern Portugal using the water supply (quantity) and soil erosion control as examples. Results show that the proposed conceptual framework is a useful tool to support land planning and forest management, adapting the provision of hydrological services to the regional biophysical and social conditions. The test of the framework across a heterogeneous region suggests that a spatially explicit combination of system property, function, service and benefit indicators can be an effective way of analysing and managing the supply and demand of the hydrological services. (C) 2014 Elsevier B.V. All rights reserved.
Spatial and temporal variation in rainfall erosivity in a Himalayan watershed
Ma, X. ; Noordwijk, M. van; Xu, J. ; Lu, X. - \ 2014
Catena 121 (2014). - ISSN 0341-8162 - p. 248 - 259.
land-cover - r-factor - climate - china - variability - catchment - river
Global climate change can modify rainfall patterns, leading to more extremes with associated erosion events. Rainfall erosivity, or the R-factor based on the Revised Universal Soil Loss Equation (RUSLE), indicates the potential water erosion risk and it plays an important role in water and soil conservation assessments. However, calculation of the R-factor requires high resolution data series, and thus we present an alternative model that can be used to accurately calculate the R-factor. Our erosivity model uses daily rainfall with advised regression parameters to estimate the R-factor in the watershed, which was selected by comparing the actual R-factor with 10 min high resolution rainfall data and the estimated R-factor with daily rainfall data from 1998 to 2002. The mean annual R-factor map was derived in the study using cokriging. The annual R-factor in the Kejie watershed was classified as medium and medium-strong erosivity, with a mean value of 3264 1.h- 1.yr- 1 which represented a range from 2505 to 5538 1.h- 1.yr- 1. A simple power relation between annual R-factor and annual rainfall was derived. The long-term change trend analysis showed no significant increasing or decreasing trend observed for the region; however, there was a significant increasing trend observed in two stations in September, one station in March. The annual R-factor with a coefficient of variation of 0.30 indicated inter-annual variation of the R-factor in the watershed was not so apparent. The intra-annual R-factor analysis illustrated the apparent seasonal and monthly distribution, about 65% from the summer season, and the maximum monthly R-factor occurring in July, followed by August and June. Consequently, the adjusted daily model can be applied in this Himalayan mountain area when high-resolution rainfall data is unavailable. The R-factor map and the simple power relation provided a useful tool for land-use planner and agriculture management in the Kejie watershed.
How climate seasonality modifies drought duration and deficit
Loon, A.F. van; Tijdeman, E. ; Wanders, N. ; Lanen, H.A.J. van; Teuling, A.J. ; Uijlenhoet, R. - \ 2014
Journal of Geophysical Research: Atmospheres 119 (2014)8. - ISSN 2169-897X - p. 4640 - 4656.
hydrological drought - low flows - catchment - reanalysis - indexes
Drought propagation through the terrestrial hydrological cycle is associated with a change in drought characteristics (duration and deficit), moving from precipitation via soil moisture to discharge. Here we investigate climate controls on drought propagation with a modeling experiment in 1271 virtual catchments that differ only in climate type. For these virtual catchments we studied the bivariate distribution of drought duration and standardized deficit for the variables precipitation, soil moisture, and discharge. We found that for meteorological drought (below-normal precipitation), the bivariate distributions of drought characteristics have a linear shape in all climates and are thus not affected by seasonality in climate. Despite the linear shape of meteorological drought, soil moisture drought (below-normal storage in the unsaturated zone) and hydrological drought (below-normal water availability in aquifers, lakes, and/or streams) show strongly nonlinear shapes in drought characteristics in climates with a pronounced seasonal cycle in precipitation and/or temperature. These seasonality effects on drought propagation are found in monsoonal, savannah, and Mediterranean climate zones. In these regions, both soil moisture and discharge show deviating shapes in drought characteristics. The effect of seasonality on drought propagation is even stronger in cold seasonal climates (i.e., at high latitudes and altitudes), where snow accumulation during winter prevents recovery from summer hydrological drought, and deficit increases strongly with duration. This has important implications for water resources management in seasonal climates, which cannot solely rely on meteorology-based indices as proxies for hydrological drought duration and deficit and need to include seasonal variation in both precipitation and temperature in hydrological drought forecasting.
Testing probabilistic adaptive real-time flood forecasting models
Smith, P.J. ; Beven, K.J. ; Leedal, D. ; Weerts, A.H. ; Young, P.C. - \ 2014
Journal of Flood Risk Management 7 (2014)3. - ISSN 1753-318X - p. 265 - 279.
series analysis - identification - catchment - systems
Operational flood forecasting has become a complex and multifaceted task, increasingly being treated in probabilistic ways to allow for the inherent uncertainties in the forecasting process. This paper reviews recent applications of data-based mechanistic (DBM) models within the operational UK National Flood Forecasting System. The position of DBM models in the forecasting chain is considered along with their offline calibration and validation. The online adaptive implementation with assimilation of water level information as used for forecasting is outlined. Two example applications based upon UK locations where severe flooding has occurred, the River Eden at Carlisle and River Severn at Shrewsbury, are presented.
Supporting IWRM through spatial integrated assessment in the Lake Naivasha basin, Kenya
Oel, P.R. van; Odongo, V.O. ; Mulatu, D.W. ; Muthoni, F.K. ; Ndungu, J.N. ; Ogada, J.O. ; Veen, A. van der - \ 2014
International Journal of Water Resources Development 30 (2014)3. - ISSN 0790-0627 - p. 605 - 618.
water-resources management - surface-water - african lake - human impact - catchment - ecology - availability - complexity - nutrients - framework
This study describes the mismatch between required knowledge and efforts by scientists and stakeholders in the Lake Naivasha basin, Kenya. In the basin, integrated water resources management (IWRM) suffers from the absence of critically relevant knowledge. This study further presents a spatial integrated assessment framework for supporting IWRM in the basin. This framework resulted from an ongoing debate between stakeholders and scientists studying the basin's issues. It builds on jointly identified indicators for sustainable governance, and their interdependency, and knowledge gaps. For IWRM in the basin this is a first important step towards a more structured debate on the implementation of IWRM.
Integrated Water Management Approaches for Sustainable Food Production
Fraiture, C.M.S. de; Fayrap, A. ; Unver, O. ; Ragab, R. - \ 2014
Irrigation and Drainage 63 (2014)2. - ISSN 1531-0353 - p. 221 - 231.
land-use - carbon sequestration - ecosystem services - climate-change - paddy fields - energy - soils - agriculture - irrigation - catchment
With a growing and increasingly wealthy and urban population, it is likely that the role of agricultural water management in ensuring food security will become more important. Pressure on water resources is high. Adverse environmental impacts as a result of sometimes poor management of irrigation and drainage are well documented, calling into question the sustainability of some of the current water management practices. Water, food, energy and climate are intrinsically connected. Greater pressure on water resources and, hence, stronger interconnectivity between sectors sharing these resources, call for new, integrated approaches to agricultural water management. This paper explores the links between water, food, energy and climate. It then explores the role of irrigation and drainage in food production and in providing other ecosystem services that are essential for the sustainable use of natural resources. The paper argues that looking at water for food production in isolation would miss important developments outside the water sector that determine the sustainability of agricultural water management. Integrated approaches to food production are not only necessary to ensure sustainability. They also lead to higher benefits per unit of water. For example, integrating food production with other ecosystem services provided by irrigation and drainage not only contributes to sustainability, it also leads to much higher economic value of benefits. This implies breaking disciplinary boundaries and encouraging greater cooperation from planning to implementation
Relationship between soil properties and the bias of N2O reduction by acetylene inhibition technique for analyzing soil denitrification potential
Qin, S.P. ; Yuan, H.J. ; Dong, W.X. ; Hu, C.S. ; Oenema, O. ; Zhang, Y.M. - \ 2013
Soil Biology and Biochemistry 66 (2013). - ISSN 0038-0717 - p. 182 - 187.
nitrous-oxide reduction - pseudomonas-aeruginosa - cultures - catchment - oxidation - sediments - nitrate - manure - assay - no
The acetylene inhibition technique (AIT) has been widely used to measure soil denitrification potential (SDP), but has been criticized also for underestimating the actual SDP due to limitations of the AIT. Possible effects of soil properties on the bias of the AIT-derived SDP have not been thoroughly investigated yet. The study presented here therefore aimed at quantifying the relationships between soil texture and nutrient contents and the bias of AIT-derived SDP. A total of 26 soils with a wide range of clay and nutrient contents were incubated according to the standard procedure of AIT for assaying SDP. Incubation flasks were made anaerobic by gas substitution with pure helium (99.999%). Changes in the N-2 and N2O concentrations in the He headspace were measured using gas chromatography. The emission rates of N2O and N-2 were calculated to quantify the bias of the AIT-derived SDP (expressed as the percentage of the actual SDP that was not accounted for by AIT). The results showed that the bias ranged from 8 to 98%. The bias was negatively correlated (P <0.05) with the clay, silt, organic matter and nutrient contents of the soils. These results indicate that the bias of the AIT-derived SDP was higher in low-fertility soils than in fertile soils. We recommend that soil properties are taken into account when interpreting results of AIT-derived SDP values. (C) 2013 Elsevier Ltd. All rights reserved.
A unit stream power based sediment transport function for overland flow
Ali, M. ; Seeger, K.M. ; Sterk, G. ; Moore, D. - \ 2013
Catena 101 (2013). - ISSN 0341-8162 - p. 197 - 204.
soil-erosion model - capacity - catchment - equations - detachment - eurosem - beds - load
Soil erosion is a serious global problem requiring effective modeling for accurate assessment of sensitive areas and related erosion rates. The outcome of soil erosion models depends strongly on the estimation of sediment transport capacity. In most of the existing spatially distributed soil erosion models sediment transport capacity of overland flow is often estimated using stream flow transport capacity functions. The applicability of stream flow functions to overland flow conditions is questionable because hydraulic conditions like flow depth, slope steepness and surface roughness under overland flow are substantially different from stream flow conditions. Hence, the main objectives of this study were i) to check the suitability of five existing well known and widely used transport capacity functions (Yalin 1963; Low, 1989; Govers, 1990; modified Engelund and Hansen (Smith et al., 1995); and Abrahams et al., 2001) for use under overland flow conditions, and ii) to derive a new function based on unit stream power by dimensional analysis to quantify transport capacity for overland flow. To accomplish the objectives, experiments in a 3.0 m long and 0.5 m wide flume were carried out using four different sands (0.230, 0.536, 0.719, and 1.022 mm). The unit discharges used for experimentation ranged from 0.07 to 2.07 x 10(-3) m(2) s(-1) and slopes ranged from 5.2 to 17.6%. In this study, none of the predictions with the existing functions was in good agreement with measured results over the whole range of experimental conditions, especially at low flow intensities. The percentages of observations in which the discrepancy ratio ranged between 0.5 and 2.0 were: 65% (Yalin 1963), 74% (Low, 1989), 57% (Govers, 1990), 54% (modified Engelund and Hansen (Smith et al., 1995)), and 25% (Abrahams et al., 2001). The results showed that the selected functions reasonably estimate transport capacities only under those ranges of conditions for which they were formulated. Although the excess.shear stress concept based function (i.e. Low's function) produced excellent results, the degree of accuracy of the results varied substantially with grain size (P.O.(0.5-2.0): 53-100%). In contrast, the performance of the Govers' function, which is based on the unit stream power concept, was quite similar for all the selected sands (P.O.(0.5-2.0): 50-63%). Based on the unit stream power concept, a new function for low flow intensities was derived by dimensional analysis using the data gained from the flume experiments. (c) 2012 Elsevier B.V. All rights reserved.
Quantitative simulation tools to analyze up- and downstream interactions of soil and water conservation measures: Supporting policy making in the Green Water Credits program of Kenya
Hunink, J.E. ; Droogers, P. ; Kauffman, J.H. ; Mwaniki, B.M. ; Bouma, J. - \ 2012
Journal of Environmental Management 111 (2012). - ISSN 0301-4797 - p. 187 - 194.
land-use change - management-practices - sediment yield - model - swat - runoff - evapotranspiration - catchment - payments - services
Upstream soil and water conservation measures in catchments can have positive impact both upstream in terms of less erosion and higher crop yields, but also downstream by less sediment flow into reservoirs and increased groundwater recharge. Green Water Credits (GWC) schemes are being developed to encourage upstream farmers to invest in soil and water conservation practices which will positively effect upstream and downstream water availability. Quantitative information on water and sediment fluxes is crucial as a basis for such financial schemes. A pilot design project in the large and strategically important Upper-Tana Basin in Kenya has the objective to develop a methodological framework for this purpose. The essence of the methodology is the integration and use of a collection of public domain tools and datasets: the so-called Green water and Blue water Assessment Toolkit (GBAT). This toolkit was applied in order to study different options to implement GWC in agricultural rainfed land for the pilot study. Impact of vegetative contour strips, mulching, and tied ridges were determined for: (i) three upstream key indicators: soil loss, crop transpiration and soil evaporation, and (ii) two downstream indicators: sediment inflow in reservoirs and groundwater recharge. All effects were compared with a baseline scenario of average conditions. Thus, not only actual land management was considered but also potential benefits of changed land use practices. Results of the simulations indicate that especially applying contour strips or tied ridges significantly reduces soil losses and increases groundwater recharge in the catchment. The model was used to build spatial expressions of the proposed management practices in order to assess their effectiveness. The developed procedure allows exploring the effects of soil conservation measures in a catchment to support the implementation of GWC.
Water quality under intensive banana production and extensive pastureland in tropical Mexico
Arya, D.R. ; Geissen, V. ; Ponce-Mendoza, A. ; Ramos-Reyes, R. ; Becker, M. - \ 2012
Journal of Plant Nutrition and Soil Science 175 (2012)4. - ISSN 1436-8730 - p. 553 - 559.
nitrite - nitrate - denitrification - accumulation - phosphorus - reduction - catchment - sediment - nitrogen
The effects of intensive banana production with high mineral-fertilizer application and of extensive pastures were compared regarding water quality in a lowland region of SE Mexico. We monitored NO, NO, and PO43– concentrations in groundwater (80 m depth), subsurface water (5 m depth), and surface water (open-ditch drainage) at monthly intervals for a one-year period. Irrespective of the land use, the NO concentrations in all water bodies were lower than the threshold value for drinking water and aquatic life. Particularly in areas with intense banana production, the NO contents in water exceeded the safety thresholds for drinking water of 1.0 mg L–1 (WHO, 2006) and aquatic ecosystems of 0.2 mg L–1 (OATA, 2008). Water from pastureland showed significantly higher PO43– concentration than that from the banana plantation, indicating a high risk of eutrophication. There is a need to provide recommendations for optimal time and amount of N application in commercial banana production and for limitation of P inputs in pasturelands to avoid further contamination of water bodies.
Modelling diffusive Cd and Zn contaminant emissions from soils to surface waters
Bonten, L.T.C. ; Kroes, J.G. ; Groenendijk, P. ; Grift, B. van der - \ 2012
Journal of Contaminant Hydrology 138-139 (2012). - ISSN 0169-7722 - p. 113 - 122.
hydraulic conductivity - automatic calibration - groundwater - catchment - flow - cadmium - netherlands - zinc - quality - copper
Modeling contaminant transport of diffusive contaminants is generally difficult, as most contaminants are located in the top soil where soil properties will vary strongly with depth and often a strong gradient in contaminant concentrations exists. When groundwater periodically penetrates the contaminated layers, stationary models (like most 3D models) cannot adequately describe contaminant transport. Therefore we have combined a hydrological instationary model using a 1D distributed column approach with a simple geochemical model to describe contaminant transport in the soil. Special to this model is that it includes lateral drainage from the soil column to different types of surface waters, which makes it possible to calculate surface water emissions especially for fluctuating groundwater tables. To test this model approach, we used it to quantify surface water emissions from soils in a catchment in the Kempen area which has been diffusively contaminated with Cd and Zn by zinc smelters. We ran the model for the period 1880–2000, starting with an uncontaminated soil in 1880. The model could describe both water discharge, surface water concentrations and current soil contents of Cd and Zn well. Further the model calculations showed that a stationary approach would underestimate leaching to surface waters considerably.
Suspended sediment load in the tidal zone of an Indonesian river
Buschman, F.A. ; Hoitink, A.J.F. ; Jong, F.M. de; Hoekstra, P. ; Hidayat, H. ; Sassi, M.G. - \ 2012
Hydrology and Earth System Sciences 16 (2012). - ISSN 1027-5606 - p. 4191 - 4204.
coral-reefs - east kalimantan - hbv model - r-factor - soil - erosion - runoff - flux - catchment - impacts
Forest clearing for reasons of timber production, open pit mining and the establishment of oil palm plantations generally results in excessively high sediment loads in tropical rivers. The increasing sediment loads pose a threat to coastal marine ecosystems, such as coral reefs. This study presents observations of suspended sediment loads in the Berau River (Kalimantan, Indonesia), which debouches into a coastal ocean that is a preeminent center of coral diversity. The Berau River is relatively small and drains a mountainous, still relatively pristine basin that receives abundant rainfall. In the tidal zone of the Berau River, flow velocity was measured over a large part of the river width using a horizontal acoustic Doppler current profiler (HADCP). Surrogate measurements of suspended sediment concentration were taken with an optical backscatter sensor (OBS). Averaged over the 6.5 weeks covered by the benchmark survey period, the suspended sediment load was estimated at 2 Mt yr-1. Based on rainfall-runoff modeling though, the river discharge peak during the survey was supposed to be moderate and the yearly averaged suspended sediment load is most likely somewhat higher than 2 Mt yr-1. The consequences of ongoing clearing of rainforest were explored using a plot-scale erosion model. When rainforest, which still covered 50–60% of the basin in 2007, is converted to production land, soil loss is expected to increase with a factor between 10 and 100. If this soil loss is transported seaward as suspended sediment, the increase in suspended sediment load in the Berau River would impose a severe stress on this global hotspot of coral reef diversity.
Assessing riparian zone impacts on water and sediment movement: A new approach
Keesstra, S.D. ; Kondrlova, E. ; Czaika, A. ; Seeger, K.M. ; Maroulis, J. - \ 2012
Netherlands journal of geosciences 91 (2012)1-2. - ISSN 0016-7746 - p. 245 - 255.
river restoration - fluvial geomorphology - bank erosion - sw slovenia - california - vegetation - catchment - transport - yield - basin
The state of river channels and their riparian zones in terms of geomorphology and vegetation has a significant effect on water and sediment transport in headwater catchments. High roughness in natural rivers due to vegetation and geomorphological attributes generate drag on flowing water. This drag will slow water discharge, which in turn influences the sediment dynamics of the flow. The impacts of changes in the management of rivers and their riparian zone (either by catchment managers or river restoration plans) impacts both up- as well as downstream reaches, and should be assessed holistically prior to the implementation of these plans. To assess the river's current state as well as any possible changes in geomorphology and vegetation in and around the river, effective approaches to characterise the river are needed. In this paper, we present a practical approach for making detailed surveys of relevant river attributes. This methodology has the benefit of being both detailed - describing river depth, width, channel morphology, erosive features and vegetation types - but also being practical in terms of time management. This is accomplished by identifying and describing characteristic benchmark reaches (typical sites) in detail against which the remainder of the river course can be rated. Using this method, a large river stretch can be assessed in a relatively short period while still retrieving high quality data for the total river course. In this way, models with high data requirements for assessing the condition of a river course, can be parameterised without major investments on field surveys. In a small headwater catchment (23 km(2)) in southwestern Poland, this field methodology was used to retrieve data to run an existing model (HEC-GeoRAS) which can assess the impact of changes in the riparian and channel vegetation and channel management on sedimentation processes and stream flow velocity. This model determines the impact of channel morphology and in-channel and riparian vegetation on stream flow and sediment transport. Using four return periods of flooding (2, 10, 20 and 100 years), two opposing channel management / morphology scenarios were run; a natural channel and a fully regulated channel. The modelling results show an increase in the effect of riparian vegetation / geomorphology with an increase in return period of the modeled peak discharge. More natural channel form and increased roughness reduces the stream flow velocity due to increasing drag from flow obstructions (vegetation and channel morphological features). The higher the flood water stage, the greater the drag due to vegetation on the floodplains of natural river reaches compared to channelised sections. Slower flow rates have an impact on sediment mobilisation and transport in the river.
Monitoring the impact of surface albedo on a saline lake in SW Russia
Argaman, E. ; Zeiliguer, A. ; Keesstra, S.D. - \ 2012
Land Degradation and Development 23 (2012)4. - ISSN 1085-3278 - p. 398 - 408.
land-use change - food security - soil-erosion - check-dams - catchment - hydrology - climate - degradation - australia - tundra
Lake Elton is located east of the Volga River in Russia and covers an area of 155¿km2. The hydrological system of the Lake and its surroundings are extremely vulnerable to climate change and human interference, but available local and regional information is sparse. Utilising climate data from 1987 to 2009 and surface albedo readings from the MODerate resolution Imaging Spectroradiometer satellite since 2000, this study analyses Lake degradation processes since 2005. Lake surface albedo analysis indicates that during the past 6¿years, lake albedo has increased dramatically from average peak values of 0·14 to 0·40. In addition, air temperature has increased by 2¿°C, and annual precipitation has decreased by 40 per cent. Moreover, human intervention in the area has increased environmental pressure on the Lake, causing a reduction of runoff inflow because of water capture, use of check-dams and water-harvesting systems. The results of the study show that, under current conditions, the Lake surface albedo is likely to remain high as compared with previous observations. The current trend implies an average 2 per cent per year increase in future annual albedo, with a maximum possible increase of 4 per cent up to a steady state of salt-crust albedo values
Comparing landscape evolution models with quantitative field data at the millennial time scale in the Belgian loess belt
Temme, A.J.A.M. ; Peeters, I. ; Buis, E. ; Veldkamp, A. ; Govers, G. - \ 2011
Earth Surface Processes and Landforms 36 (2011)10. - ISSN 0197-9337 - p. 1300 - 1312.
soil-erosion - land-use - hillslope evolution - dem resolution - redistribution - tillage - topography - deposition - catchment - water
This study compares three landscape evolution models and their ability to correctly simulate measured 2500¿year landscape evolution in two small catchments in the Belgian loess belt. WATEM LT and LAPSUS both model tillage and water erosion and deposition and have detachment-limited descriptions for water erosion and deposition. Equations in LAPSUS are more mechanistic than those in WATEM LT. WATEM LTT resembles WATEM LT, but is a transport-limited model. All three models are DEM-based. Calibration and validation simulations were performed forward in time on (1D) transects for four spatial resolutions, and backward in time for (2D) catchments at 20¿m resolution. For transects, model outputs were compared with discretized observations of transect shape. For catchments, outputs were compared with point observations of palaeo-altitude, averaged over landscape element classes. For transects, the three models performed well, resulting in model efficiency factors of 0.92 to 0.99 for calibration and 0.62 to 0.96 for validation. However, for catchments, simulations showed that the transport-limited WATEM LTT model could not realistically simulate long-term landscape evolution. Performance of WATEM LT and LAPSUS at catchment scale was similar to that on transects, although LAPSUS has problems with backward calculation. Tests demonstrate that a transport-limited approach cannot be used to model long-term landscape evolution in the Belgian loess belt, which is in agreement with theoretical and empirical understanding of soil erosion processes in this environment. The difference in performance between transport-limited and detachment-limited models is clear only when the models are evaluated in a 2D catchment. The lack of such distinction when models were applied in a 1D transect highlights the importance of evaluating landscape evolution models in a 2D setting so that effects of flow convergence/divergence can be accounted for. Copyright © 2011 John Wiley & Sons, Ltd
Spatial pattern and temporal variability of runoff processes in Mediterranean Mountain environments - a case study of the Central Spanish Pyrenees
Butzen, V. ; Seeger, K.M. ; Casper, M.C. - \ 2011
Zeitschrift für Geomorphologie 55 (2011)3. - ISSN 0372-8854 - p. 25 - 48.
catchment - generation - basin - moisture - behavior - spain
Mediterranean mountain environments like the Central Spanish Pyrenees show a highly variable rainfall-runoff response, mainly explained by the intense intra- and inter-annual variability of precipitation yield. This leads to a highly differentiated moisture status and therefore it is assumed to lead also to highly variable runoff contributing areas. For the identification of areas with certain dominant runoff processes in an experimental headwater catchment in which agriculture was abandoned several decades ago the concept of the topographical index was extended by means of weighting grids. These weighting rasters were generated using additional information on soils and vegetation. Runoff generating areas were identified widespread in the catchment, with Hortonian overland flow (HOF) dominating the runoff processes on degraded soils, and saturation overland flow (SOF) dominating the footslope areas, where hydromorphic soils were mapped. Rainfall-runoff experiments were performed to quantify runoff and erosion and to identify seasonal changes using experimental data gained in different seasons of the year. The seasonal changes in runoff response could be localised clearly within the areas of SOF, whereas the other ones showed a similar behaviour. This implied that the procedure of delineation had to be differentiated for dry and moist conditions, and that the SOF areas had to be reclassified as SSF/DP areas for dry conditions. Due to the location of these areas close to the ravine, we could explain the pronounced switching runoff behaviour of the catchment. GIS techniques combining different levels of topographic, soil and vegetation information showed to be suitable for delineation of areas with different runoff generation processes. The inclusion of seasonally distributed experimental data demonstrated that for dry conditions, slightly different methods have to be applied. Nevertheless, the study showed also the limitations of the combined methods: (I) subsurface flows and ground water recharge could only be deduced, not demonstrated, (II) finally, there is still a good knowledge of the area needed for an accurate process representation.
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