Willem Petrus de Clercq

Willem Petrus de Clercq
Stellenbosch University | SUN · Stellenbosch University Water institute

PhD BioSciece Engineer

About

75
Publications
20,578
Reads
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716
Citations
Citations since 2016
41 Research Items
600 Citations
2016201720182019202020212022020406080100
2016201720182019202020212022020406080100
2016201720182019202020212022020406080100
2016201720182019202020212022020406080100
Additional affiliations
January 2015 - February 2017
Stellenbosch University
Position
  • Senior Researcher

Publications

Publications (75)
Book
Digital elevation model (DEM) data are elemental in deriving primary topographic attributes which serve as input variables to a variety of hydrologic and geomorphologic studies. There is, however, still varied consensus on the effect of DEM source and resolution on the application of these topographic attributes to landscape characterization. At th...
Article
Topsoil bleaching is a common occurrence in South African soils. Bleaching is usually associated with the removal of soil pigmenting agents through redox stripping, clay eluviation and/or podzolisation. Thus topsoil bleaching above non-podzolic, high chroma red and yellow, supposedly well-drained subsoils is difficult to explain. These deep, weakly...
Preprint
Full-text available
Understanding the soil-geomorphology relationships within the context of landscape evolution is one of the fundamental tasks of soil science. The soils in the valleys of African rivers are strongly influenced by the long history of weathering and fluvial sediment transport, which unlike the valleys of the Northern temperate regions, have not been a...
Article
Continual advances in quantitative modelling of surface processes, combined with new spatio-temporal and geo-computational algorithms, have revolutionised the auto-classification and mapping of landform components through the automated analysis of high-quality digital elevation models (DEMs). Digital geomorphic mapping (DGM) approaches that can sim...
Article
Full-text available
en Expanding arable land under irrigation is cardinal in the quest to attain Africa's aspiration of transforming agriculture and realizing its true value and positive impact on wealth creation, economic growth, food security and nutrition for all. Over the last three to four decades, many initiatives have been designed to harness both small‐ and la...
Article
Landform elements (LFEs) are commonly used in soil science to demark pedological boundaries and as a first indication of soil spatial variability. A novel LFE classification system known as geomorphons, has been shown to be able to overcome limitations of other automated LFE classifiers. The pattern recognition algorithm classifies the 10 most comm...
Article
Full-text available
Accurate DEM-derived streamlines and catchment boundaries are essential for hydrological modelling. Due to the popularity of hydrological parameters derived mainly from free DEMs, it is essential to investigate the accuracy of these parameters. This study compared the spatial accuracy of streamlines and catchment boundaries derived from available d...
Preprint
Full-text available
This study aimed to establish if landform elements classified through aggregated Geomorphons can stratify multiple soil properties.
Article
Full-text available
River systems that support high biodiversity profiles are conservation priorities worldwide. Understanding river ecosystem thresholds to low-flow conditions is important for the conservation of these systems. While climatic variations are likely to impact the streamflow variability of many river courses into the future, understanding specific river...
Article
Spatial information on soil particle size distribution and soil organic carbon (SOC) are important for land-use management, environmental models and policy-making. Digital soil mapping (DSM) techniques can quantitatively predict these soil properties using minimal resources. However, DSM has not been adequately evaluated at the farm-scale. The aim...
Poster
Full-text available
Climate change is driving increased variability in precipitation patterns across much of southern Africa, making it challenging to model catchment-scale water dynamics using historical data. This has implications for effective water management particularly in water scarce areas which have competing users. Agriculture is an important water user whic...
Article
Knowledge of soil depth spatial variability is important for land use management especially in dryland agriculture regions, which rely on climate and soils to provide adequate water and nutrients during the growing season. Soil spatial variability can be predicted from legacy soil data through machine learning techniques producing quantitative soil...
Article
Full-text available
The water-energy-food nexus has emerged as a useful concept to understand the multiple interdependencies that exist between the water, energy and food sectors. The nexus is an ambitious attempt to work across disciplines and scales to understand the workings of these complex systems. It is, however, criticised for being more of a general framework...
Chapter
Full-text available
South Africa’s water policy has been criticised as an inefficient instrument to achieve the social goals of appropriately redistributing water in informal settlements. Growing global water challenges have demonstrated that Traditional Water Management methodologies based on improving the material conditions of impoverished informal settlements are...
Preprint
Full-text available
River systems that support high biodiversity profiles are conservation priorities world-wide. Understanding river eco-system thresholds to low flow conditions is important for the conservation of these systems. While climatic variations are likely to impact the streamflow variability of many river courses into the future, understanding specific riv...
Conference Paper
This research serves as a preliminary study to map the whole Sandspruit catchment in the Western Cape, South Africa for hydrological modelling and agricultural management. This study represents the first study in South Africa evaluating feature selection techniques combined with supervised machine learning to map soil spatial variability. The objec...
Article
Full-text available
Water is a critical resource necessary to support social and economic development. Economic growth and, in particular, the growth of urban and peri-urban areas, however results in declining water quality which threatens water-dependent industries. In developing countries this is a particular concern due to the rapid rate of urbanisation and the lim...
Chapter
Full-text available
Along the west coast of South Africa, where precipitation rates are often less than 400 mm/year and rivers are mostly ephemeral, access to water is a critical limitation on development. However, west coast groundwater is variably saline in areas, can damage sensitive ecological systems, and is often not suitable for domestic or agricultural use. SA...
Article
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Soil quality is widely regarded as an important factor in sustainable agriculture and is often assessed by evaluating the pertinent physical, chemical and biological properties of soils. The aims of this study were to (i) establish a minimum data set (MDS) of soil quality parameters capable of monitoring changes in soil condition and ecosystem func...
Article
Full-text available
A comprehensive river basin assessment is key to integrated land and water resources management (ILWRM), which is based on an integrated system analysis to identify interacting hydrological processes that are driven by landscape features and socioeconomic development. Software toolsets like RBIS (River Basin Information System), GRASS-HRU, and the...
Article
Full-text available
Groundwater vulnerability is normally associated with the potential for contamination, for example the DRASTIC approach, but the increasing importance of groundwater in human, agricultural, and industrial systems, implies that groundwater vulnerability is dependent on a range of other parameters and particularly parameters impacted by climate chang...
Article
Full-text available
Agriculture in developing countries will have to transform and increase production by an estimated 70% in order to meet demands by 2050. Although well-managed commercial farms offer little manoeuvring space for increasing agricultural water productivity, smallholder farms usually operate at low input costs and therefore provide ample opportunities...
Article
Full-text available
Automatic weather stations (AWSs) serve a number of goals in the SASSCAL context and beyond. A sufficient cover and density in geographical space is needed to record spatial climatic variability and to feed climate models and forecast services. In addition, research projects using an ecosystem approach require robust information on local weather. I...
Article
Wetlands are conservation priorities worldwide, due to their high biodiversity and productivity, but are under threat from agricultural and climate change stresses. To improve the water management practices and resource allocation in these complex systems, a modelling approach has been developed to estimate potential recharge for data poor catchmen...
Conference Paper
Full-text available
With the advancement in digital elevation model accuracies and scales, automated catchment delineation has become more widely used to reduce cost, time and errors that can occur during manual delineation. However, this type of delineation does not consider possible influxes of groundwater due to geological structures, such as dipping of bedding pla...
Article
Full-text available
The purpose of the study is to assess whether Corporate Social Responsibility regarding water is considered relevant for sustainability in companies related to agriculture in South Africa, considering that their impact directly influences public access to water. To accomplish this purpose, a qualitative approach was developed through the study of t...
Poster
Full-text available
Wetlands are areas that are saturated, either by surface or groundwater, and where vegetation has adapted to periods of saturated soil conditions. These systems are regarded as one of the most productive ecosystem on Earth, providing valuable functions in filtering water, collecting sediments and retarding flow during flood events. Of concern to th...
Article
Clay mineralogy of the fluvial plains reflects the complexity of geological setting, material weathering and transport. Clay minerals produced in the weathering process are closely associated with the parent rock and serve as an indicator of the material sources. Soil clay mineralogy of South African river valleys is insufficiently studied and this...
Article
Full-text available
Cocoa agroecosystems are a major land-use type in the tropical rainforest belt of West Africa, reportedly associated with several ecological changes, including soil degradation. This study aims to develop a composite soil degradation assessment index (CSDI) for determining the degradation level of cocoa soils under smallholder agroecosystems of sou...
Poster
Full-text available
Considering projected climate and socio-economic development for Southern Africa, a major challenge in southern Africa is to find mechanisms to adapt to climate change and to secure water at sufficient quality and quantity for both, human well-being and the stability of ecosystem functions and services. Many countries of southern Africa face inadeq...
Article
Full-text available
Cocoa agroforestry is a major landuse type in the tropical rainforest belt of West Africa, reportedly associated with several ecological changes, including soil degradation. This study aims to develop a composite soil degradation assessment index (CSDI) for determining the degradation level of cocoa soils under smallholder agroforests of southwest...
Article
The objectives of this paper are twofold: (i) to calibrate and validate the PILOTEN crop model for tomato (Solanum lycopersicum L.), and (ii) to use the model to examine the response of tomato yield to different irrigation and fertilization scheduling scenarios under varying climatic conditions in order to draw up management recommendations for sma...
Article
Full-text available
Gullies are complex erosive systems inducing significant soil losses, and have been linked to land degradation worldwide, and have been shown to have significant impacts in locations with Mediterranean climates. Addressing the research deficit of methods allowing for a comparison of driving processes and structures, high resolution imagery and GIS...
Conference Paper
Full-text available
Hydrological modelling is a useful method to predict water availability and environmental impacts in a range of climate and land use change scenarios. One of the major challenges to accurate predictions using hydrological modelling in semi-arid areas is the high temporal and spatial variability of rainfall events and the associated uncertainty of r...
Technical Report
Full-text available
For the Letaba basin situated in the South African part of the Limpopo basin, a hydrological study was carried out in order to quantify the effect of smallholder farming on river flows. Important was to study the consequences of improved agricultural systems on the river flows, in particular for the Kruger National Park situated in the lower part o...
Article
Full-text available
The consumption of semi-domesticated indigenous vegetables such as Corchorus olitorius is being promoted in South Africa. Presently, cultivation of indigenous vegetables is hampered by the absence of cultivation guidelines due to lack of agronomic research on the various production aspects. The current study evaluated the yield of C. olitorius in r...
Article
Full-text available
Estimation and mapping of soil organic carbon storage in three dimensions for large areas is increasingly in demand for climate change reporting, but such estimates at large spatial scales and different soil depths are generally time consuming and expensive. This paper investigates the potential to reduce the number of required soil observations to...
Article
Full-text available
A major task of the newly established "Southern African Science Service Centre for Climate Change and Adaptive Land Management" (SASSCAL; www.sasscal.org) and its partners is to provide science-based environmental information and knowledge which includes the provision of consistent and reliable climate data for Southern Africa. Hence, SASSCAL, in c...
Poster
The Verlorenvlei catchment is located in South Africa within the Sandveld area and is exposed to several challenges, such as climate change and limited access to fresh water combined with increasing irrigation agriculture. The area represents a hydrological vulnerable area within the Sandveld. It is one of the most important estuary systems in the...
Article
Full-text available
Soil and stream salinisation is a major environmental problem because it reduces the productivity of landscapes and degrades water quality. The Berg River (South Africa) has been exhibiting a trend of increasing salinity levels, which has primarily been attributed to the manifestation of dryland salinity. Dryland salinity occurs as a result of chan...
Article
Full-text available
Contour bank farming is a well-known agricultural management technique in areas which are characterised by intensive and erosive rainfalls. Contour banks are designed to reduce the flow velocity of overland flow and to intercept water before it concentrates in rills, thereby reducing the risk of soil erosion and land degradation. By their structure...
Article
Full-text available
Wild vegetables are an important commodity in the subsistence farming sector. They are considered to be rich in micronutrients and can therefore be used to overcome inadequate nutrition. However, research on micronutrients in wild vegetables remains limited and sporadic. In this study, we evaluated the responses of two wild vegetables - Corchorus o...
Article
Full-text available
Little is known about the effects of residue burning or retention on nutrient leaching during the inter-rotation of clonal Eucalyptus grown on the sandy soils of subtropical Zululand, South Africa. A study compared zero-tension nutrient leaching through the top metre of soil at depths of 0.15, 0.5 and 1.0 m in an undisturbed crop with adjacent clea...
Article
Land component boundaries often coincide with transitions in environmental land properties such as soil, climate and biology. Image segmentation is an effective method for delineating terrain morphological units from digital elevation models (DEMs). This paper compares the land components derived from five DEMs. The second version of the 30-m advan...
Book
Within the framework of the EC support project to the Water Centres of Excellence one the project’s tasks was to improve water sector knowledge development and management in the region; consequently the CoEs were requested to develop relevant educational material in the form of academic training courses. Within the Southern African Network, the exe...
Article
In the Western Cape region of South Africa, the intensification of agricultural land-use has caused a significant loss of the natural Renosterveld vegetation over the last 100 years. Renosterveld (Elytropappus Rhinocertis, "Renosterbos") of the Western Cape region forms part of the endemic Fynbos biome located in the South African Cape region. Only...
Article
Full-text available
Wild vegetables (WV) are an important source of food in the maize based subsistence farming sector of rural South Africa. Their main role is as relish as they are used as an accompaniment for staple cereal based diets. They are generally reported to be rich in micronutrients. Although they may be consumed in small quantities, they influence the int...
Article
Soil salinization is a land degradation process that leads to reduced agricultural yields. This study investigated the method that can best predict electrical conductivity (EC) in dry soils using individual bands, a normalized difference salinity index (NDSI), partial least squares regression (PLSR), and bagging PLSR. Soil spectral reflectance of d...
Article
Full-text available
A detailed water balance and conceptual flow model was calculated and developed for the Sandspruit catchment for the period 1990 to 2010 on a winter rainfall water-year (1 April - 31 March) basis. The Sandspruit catchment (quaternary catchment G10J) is located in the Western Cape Province of South Africa and is a tributary of the Berg River. It con...
Article
Full-text available
The effects of clearfelling and subsequent residue retention or burning on water and nutrient balances needs to be understood and quantified on forest sites that are sensitive to loss, so that the long-term sustainable productivity of such sites can be maintained and promoted. An experimental site was established in a clonal eucalypt compartment on...