Study region: Two-Streams catchment, KwaZulu-Natal Midlands, South Africa. Study focus: The impacts of Acacia mearnsii plantations on hydrological processes including groundwater is investigated using the Two-Streams experimental catchment as a case study site. Integrated hydrological, hydrogeological, hydrochemical and environmental isotope methods were adopted. Groundwater recharge is estimated using the chloride mass balance (CMB) method, and baseflow is separated using digital filters and delta O-18 isotope approaches. The direct and indirect impacts of the tree stands on groundwater including on recharge, groundwater level and baseflow are assessed. New hydrological insights for the region: Systematic analyses of all the hydrological data show that direct groundwater uptake by tree roots at the Two-Streams catchment would not be possible due to limiting root depths. However, there is clear evidence on the impacts of the tree stands on groundwater levels and baseflow at the study site. Thus, in instances where the regional groundwater is not available for direct abstraction by tree roots, trees can have considerable impacts on groundwater by extracting water from the unsaturated zone, reducing recharge to aquifers, without having direct access to the groundwater proper. The impact of Acacia mearnsii plantations on groundwater which are observed in terms of reductions in groundwater recharge and consequent reduction in groundwater levels and baseflow starts to be observed on average six years after planting.

The failure of tailings storage facilities (TSFs) results in the discharge of significant quantities of hazardous waste material into the natural environment. Research studies relating to slope instability have identified physical mechanisms such as rainfall-induced erosion, liquefaction, and shear failure as the main triggers. The generation of transient pressure waves and the mobilization of pre-event water in the unsaturated zone have been found to trigger shallow landslides in natural hillslopes. In this paper we review these physical mechanisms, known as groundwater ridging (GWR) and the Lisse effect (LE), from other studies. Previous researchers have explained both these phenomena through field and laboratory observations, numerical modelling, as well as conceptual discussions. These case studies demonstrate the impact of rainfall characteristics on the generation of transient pressure waves that rapidly increase the phreatic surface and change pore water suction. Reference is also made to the influence and behaviour of physical porous medium characteristics on the establishment of a continuous water phase that facilitates the transmission of an induced pressure head. However, previous studies fail to recognize the possibility that the pressure increase in pre-event water through pore air propagation could cause slope instability in tailings dams. The authors suggest that the physical properties and hydraulic behaviour of unsaturated porous tailings media make it susceptible to GWR and the LE, resulting in the creation of a potential failure plane.

Processes linked to woody plant encroachment in grassland are still not well understood, especially the interactions between trees and soil water availability. Our aim was to study the depth of water uptake by trees in grassland and its controlling factors. We studied water uptake in Vachellia sieberiana trees (hereafter called ‘acacias’) in a humid grassland of South Africa. We especially studied the effect of size classes of acacias and their position in the catena on water potential (ψ) of acacia leaves and water uptake depth of acacias across seasons, as inferred from isotope δ18O values of soil and stem water samples. Acacias were more water stressed in February (wet season) with the most negative water potentials. Taller acacias (>3 m height) were more water-stressed (ψ ± SD = −1.62 ± 0.81 MPA) than smaller acacias (<1 m height) (ψ ± SD = −1.32 ± 0.80 MPA). In September (end of dry season), all tree size classes uptake water equally in A and B soil horizons. In February (middle of the wet season), tall, medium and even small trees favoured the B horizon. Small trees had similar plasticity in water uptake to taller trees and could modify depth of water uptake between seasons. This process could increase their probability of becoming adults, and may favour tree encroachment in grasslands.

The Wetlands in Drylands presented in this study focussed on the Papenkuils Wetland, which is in the Western Cape of South Africa, north of the Brandvlei Dam, and south west of Worcester, downstream of the confluence of the Breede (or Bree) and Smalblaar Rivers. This study sets out to establish the shadow price of the environmental services of this wetland, and to understand how this value changes with the possible future diversion of water to an agricultural dam before the Wetland, water provision to the wetlands. The study strongly recommends that the functionality of this wetland, as the largest in the Breede (Afrikaans word meaning wide) Catchment and with biodiversity that is recognised as an important remnant of habitats in the region, be maintained through management and sufficient inundation of water. This would be accompanied by a programme of abstraction for irrigation at a pumping station below the Papenkuils Wetland, as opposed to further abstraction of winter water above the wetland, as is currently proposed.

With an increasing population, development of the country and a changing climate, demand for fresh water has increased and is coupled with negatively impacted water resources. One impacted component of the water resource may have an impact on another, due to the interaction between water resource components in the water cycle. All water resource components need to be well-managed and protected to ensure their availability and sustainability. Studies on water quantities, flow dynamics, quality, and contamination are essential in this regard. Isotopes are used as a tool in these studies to define the interconnection between different water resource components. The information gained from isotope studies is valuable in the planning of activities in areas where interacting water resource components may potentially be affected. A study focused on impacts on the water resource from large scale burials is presented (Middelburg, Mpumalanga). A seasonal wetland is located downgradient of the cemetery, between the cemetery and a stream that flows past the cemetery. In order to assess possible flow pathways from the cemetery to the stream, monthly monitoring of surface and groundwater quality and level fluctuations was carried out on the stream, as well as existing and newly installed boreholes at the site. The water samples were analysed for inorganic constituents, tritium, and stable water isotopes. The isotope results revealed the influence of rainfall and shallow groundwater contributions to streamflow, while groundwater provides baseflow as the stream level recedes. The depth to groundwater reduced with increasing rainfall, indicating direct recharge. The difference in concentrations of some inorganic parameters in the stream compared to the groundwater at the cemetery revealed the effect of natural attenuation and the wetland acting as a filter to improve the water quality of the shallow interflow.

The semi-arid conditions in savanna landscapes ensure that ephemeral drainage dominates the hydrological network in these dryland systems. Quantification of their hydrological processes is important to inform ecosystem understanding and future conservation efforts under a changing climate, and to provide guidance for restoration. By combining in situ hydrometric observations, hydrochemistry, remote sensing and a soil water balance model, we characterise the groundwater–surface water interactions in ephemeral low-order catchments of the granitoid regions of the southern Kruger National Park (KNP). Streams at the lowest orders are augmented by lateral interflows from the catena, although the second- and third-order stream reaches are conduits for groundwater recharge to the fractured rock aquifer; the soils of the crests and foot-slopes also show preferential flow, and are truly recharge soils, whilst the duplex soils of the midslopes clearly show their responsive nature to a low soil moisture deficit in the shallow horizons. Actual evaporation (aET) differed between catena elements with surprisingly little variation at third-order hillslopes, with the greatest overall aET at the first order. Meanwhile, soil water balances demonstrated a significant variation in storage of the riparian zones as a result of interflow from upslope and aET losses. Furthermore, data support broader-scale observations that groundwater recharge through the vadose zone to the fractured rock aquifer is dependent upon threshold antecedent precipitation conditions. Moderate precipitation events (5 mm/day – 35 mm/day) over a 2–3 week period initiate groundwater responses with a 2–3 month lag, whilst intense precipitation events (100 mm/day) are expressed within 2–3 weeks.Conservation implications: Understanding the lateral connectivity of terrestrial ecosystems to the ephemeral drainage network expressed via hydrological processes in these savanna landscapes is important to infer potential impacts of climate variability on the continued conservation of these ecosystems, both within and external to protected areas.

Urbanization and hydrology have an interactive relationship, as urbanization changing the hydrology of a system and the hydrology commonly causing structural damage to the infrastructure. Hydrological modelling has been used to quantify the water causing structural impacts, and to provide solutions to the issues. However, in already-urbanized areas, creating a soil map to use as input in the modelling process is difficult, as observation positions are limited and visuals of the natural vegetation which indicate soil distribution are unnatural. This project used historical satellite images in combination with terrain parameters and digital soil mapping methods to produce an accurate (Kappa statistic = 0.81) hydropedology soil map for the Cosmo City suburb in Johannesburg, South Africa. The map was used as input into the HYDRUS 2D and SWAT hydrological models to quantify the water creating road damage at Kampala Crescent, a road within Cosmo City (using HYDRUS 2D), as well as the impact of urbanization on the hydrology of the area (using SWAT). HYDRUS 2D modelling showed that a subsurface drain installed at Kampala Crescent would need a carrying capacity of 0.3 m3·h−1·m−1 to alleviate the road damage, while SWAT modelling shows that surface runoff in Cosmo City will commence with as little rainfall as 2 mm·month−1. This project showcases the value of multidisciplinary work. The remote sensing was invaluable to the mapping, which informed the hydrological modelling and subsequently provided answers to the engineers, who could then mitigate the hydrology-related issues within Cosmo City.

Savannas make up about 20% of the global land-surface and are dependent on fires to maintain a balanced ecosystem. Fires in other fire-driven landscapes, particularly wildfires, were found to have negative effects on various soil properties. However, there is a lack of studies confirming the effect of fires on soil hydrology in African savanna soils. A long-term fire experiment in a South African savanna provided an opportunity to investigate the effect of different prescribed fire frequencies on soil properties in situ across coarse-grained granitic and fine-textured basalt-derived soils. Soil properties were compared between soils exposed to annual fires, fires every 2-4 years and where fires have been excluded for approximately 60 years. Across all three fire treatments, unsaturated hydraulic conductivity (K-unsat) was measured using a Tension Disc Infiltrometer to infer infiltration rates, saturated hydraulic conductivity (K-sat) measured with a Guelph Permeameter, soil water potential calculated using a Decagon WP4-T Dewpoint Potentiometer to infer soil water retention and soil total C and N measured using a LECO CNS TruMac Series Analyser. Our study found that K-unsat is not affected by frequent annual fires which have infiltration rates similar to soils where fires have been excluded for nearly 6 decades. However, recently burnt granitic soils, i.e. three months prior, have significantly slower K-unsat which were as low as < 1 mm hr(-1) compared to a mean K-unsat of 30 mm hr(-1) on annually burnt soils, alluding to short term fire impacts on soil infiltration. Hence, we believe that time following a fire plays a greater role on K-unsat than fire frequency. Fires did not affect K-sat within the initial 2-5 cm of the soil surface. In general, the granitic soils had faster K-unsat and K-sat than the basaltic soils. Soil water potential, total C and N was significantly greater in the fire exclusion sites over both parent materials. Soil water and nutrient availability is critical in a post-fire environment to facilitate vegetation recovery in African savannas. These systems are resilient to fires which do not have long-term negative impacts on soil hydrology and nutrients, but instead increases the spatio-temporal variation in soil properties necessary in maintaining savanna heterogeneity.

Abstract With the world's growing population and our limited natural resources, there is a need to produce more food using fewer inputs, especially fresh water. Water is a critical resource in agriculture and may be more of a limiting factor than other crop growth requirements. As water availability is impacted by climate change and competition from human consumption and other industries, methods of improving crop water use efficiency (WUE) through conservation of water and the enhancement of crop growth need to be employed to meet our growing demands sustainably. The research assessed the differences in soil water status between organically farmed crops with a grass mulch and conventionally farmed crops without mulch, to use the water resource more efficiently. This research, conducted at the Mandela long-term organic farming systems research trial site at Nelson Mandela University, George Campus in South Africa's Southern Cape, is part of a larger research project (the Mandela Trials) in which various researchers have covered agronomy, microbiology and pest and disease control. The organic treatment had a significantly higher soil water content (SWC) than the conventional treatment at all soil depths over the two seasons 2016/17 and 2017/18. Theta probes showed that in both seasons, for the top 6 cm of soil the organic treatment had a higher SWC than the conventional treatment. The minimum and median SWC in the organic treatment were much higher than that of the conventional and control. However, in the second season the control treatment had a higher minimum SWC than the organic, but a lower median SWC (there was almost no plant growth on the control plots due to nutrient deficiencies). The differences in the SWC of the organic and conventional treatment for 2016/17 was significant, however, differences for 2017/18 were not significant. The capacitance probe data for the 10 cm depth show that the minimum and median SWC of the organic treatment were higher than the conventional. The differences in SWC between all three treatments are statistically significant for both seasons. The combined SWC capacitance probe data of the 0-50 cm soil profile showed that the organic treatment had a higher SWC and median than the conventional treatment. However, the control treatment had the highest SWC and median of all the treatments. There was a significant difference in the organic and conventional treatments in both seasons, but no significant difference between the organic and control treatments in the first season. Soil carbon was significantly higher in the organic treatment, than the conventional. Organic farming methods preserve and promote an increase in soil organic matter (SOM), thus improving the soil structure and increasing the soil's water holding capacity. From this research, it is recommended that organic farming practices can be used to help conserve SWC, keeping it available to crops for longer and helping farmers make more efficient use of this scarce resource. This is especially relevant for low rainfall areas which are affected by water shortages. Improved SWC availability should be coupled with good agronomic practices to increase productive water losses (plant use) and the conversion of water to yields, increasing WUE. Adding organic matter to the soil will improve resilience and help sequester carbon, and thus mitigate climate change. More research is needed to assess what proportion of the increased soil water retention can be attributed to the influence of the mulch and what effect the SOM had.

The rate and direction of groundwater flow are a function of the gradient of the hydraulic head, whose components are gravity head and pressure head. This paper presents results and analyses of field observations of pressure head responses to some rainfall events of 2000/2001 summer season in a headwater catchment in South Africa. A transect spanning from a steep hillslope zone, through a transition zone and a flat low-lying wetland zone, to a stream channel zone was instrumented with tensiometers to monitor the responses of pore-water pressure to rainfall. The season’s late rainfall events simultaneously caused the pressurized pore-air driven Lisse effect water table response at the transition zone, and the capillary fringe-assisted groundwater ridging water table response at the wetland zone. During the events, the Lisse effect dissipated, but followed by sequences of stepped increases in pressure head in the deep soil profile at the transition zone. These stepped increases in pressure head, whose magnitudes increased with depth, were caused by the upwelling pressure heads induced by rainfall spike intensities at the wetland zone. These upwelling pressure heads could have major and disproportionate influence on the dynamics of groundwater flow.

Near-surface and lateral ow discharge comprise an o en neglected pathway for contaminant movement from mine wastes toward downslope water resources. Contaminant loads moving through near surface pathways can exceed contaminant loading via surface water or groundwater uxes. Hydropedological surveys to identify and quantify these near-surface uxes provide an e ective method to evaluate the potential impacts via this pathway. is paper describes the methodology of hydropedological surveys and their application in two hard-rock mining sites. Conceptual hydrological response models were developed which assisted with the understanding of mechanisms, modelling and monitoring of contaminant migration from the sites.

Maize (Zea mays L.) is the staple food crop grown by most smallholder farmers in South Africa. Decline in soil fertility and expensive chemical fertilisers affect maize production by these farmers. Smallholder farmers cannot afford chemical fertilisers because these are expensive. Agroforestry systems offer cheap alternatives to expensive chemical fertilisers. A field experiment was established in the 2015/16 season at Wartburg. The objective of the study was to evaluate maize yields and productivity in agroforestry systems. The experiment had five treatments: sole (maize; pigeonpea; or Sesbania bispinosa); maize + Sesbania bispinosa; maize + pigeonpea laid out in a randomized complete block design replicated three times. The yield was in order: sole maize > maize + pigeonpea ≥ maize + pigeonpea. The land equivalent ratio (LER) was in the sequence maize + pigeonpea > sole pigeonpea > maize + S. bispinosa > sole S. bispinosa ≥ sole maize. Maize yield might be increased in the following season as a subsequent crop in the same field because of residual nutrients that would have been enhanced and set free for plant uptake during the previous season. Pigeonpea is recommended in agroforestry systems with maize because of its higher LER and combined production of grain for human and livestock consumption and firewood.

Deposition of large quantities of mining waste can have negative impacts on surface and ground water resources. ese impacts necessitate amelioration of the wastes through various measures, but primarily through a cover system. ese covers are designed to restrict percolation of rain water through the waste material, and thereby restrict moving contaminants to groundwater, either through retention and subsequent evapotranspiration, or by water shedding. Cover systems in semi-arid areas require particularly careful design and performance evaluation in order to provide a sustained rst defence to impacts. is study assesses the performance of covers comprising vermiculite material over waste rock and tailings.

Core Ideas Hydropedology can serve as an indicator of the hydrological behavior of catchments. Hydropedological interpretations are applicable at regional scales. Internal catchment properties are often more important than environmental factors. Understanding and quantifying groundwater–surface water interactions is important for effective water resource management. Characterization of these interactions is difficult due to heterogeneities in landscapes and difficulties in measuring hydrological processes at different scales. Although soils play an integral role in the hydrological functioning of landscapes, very few groundwater–surface water interaction studies consider soils as key components of hydrologic variation. We studied 21 catchments in South Africa with available stream attributes, such as baseflow index (BFI) and hydrological variability (CVB). The soils of the catchments were interpreted and grouped into four classes based on dominant hydropedological response: Recharge, Interflow, Responsive (shallow), and Responsive (wet). The dominant soil distribution patterns in the catchments were then determined. Significant positive Spearman correlation coefficients exist between BFI and soil attributes such as depth (0.72), clay content (0.54), and the area covered by Recharge soils (0.81). The occurrence of Interflow and shallow soils is inversely correlated to BFI (−0.86 and −0.67, respectively), whereas CVB was positively correlated to the area of Interflow soils (0.81) and negatively to the area of Recharge soils (−0.75). Based on the hydropedological soil distribution pattern, three conceptual models of groundwater–surface water interactions were constructed: (i) those where vertical drainage and recharge of groundwater in the upper slopes are dominant, with return flow to soil layers in lower‐lying positions, and soil and groundwater contribute to streamflow; (ii) those where vertical drainage through soils and recharge of groundwater is dominant in upper and lower lying landscape positions, there is no return flow to soils, and only groundwater contributes to streamflow; and (iii) those where lateral flow at the soil–bedrock interface is dominant throughout the catchment, limited recharge occurs, and the stream is fed through lateral flow from soils with limited contribution from groundwater.

The problem of transmission of pressure head through the zone of tension saturation in the Lisse effect (LE), i.e., the rapid response of groundwater level to pressurized pore air in the unsaturated zone, is investigated theoretically and experimentally. From the law of conservation of energy and the continuity equation, a one-dimensional diffusion equation is derived for transmission of pressure head through the zone of tension saturation. The solution to the equation is the pressure head at any point below the upper boundary of the zone of tension saturation and at any time after the compressed pore air pressure is imposed on the boundary. The key parameter, which determines the behaviour of transmission of pressure head, is the newly proposed pressure head diffusivity coefficient. The theoretical results agree with the experimental results, obtained from laboratory column experiments in three physically different soils.

Previous studies indicate that most rainfall-triggered shallow landslides are initiated by a spiked rainfall-intensity, which typically occurs several hours into a critical rainfall event, in which the slide is triggered. The critical rainfall event also usually occurs after several days of the antecedent rainfall. Rainfall triggers landslides via rapid increase in pore-water pressure, commonly associated with rapid infiltration. However, based on the above timings of landslide occurrences, this paper argues that the rapid increase in pore-water pressure is a result of diffusive and rapid transmission of intense-rainfall induced pressure-head into a tension saturated (or near-saturated) soil profile. This argument is supported by a conceptually new pressure-head diffusion equation. Antecedent and critical rainfalls are significant in creating tension saturated continuous pore-water phase, necessary for the rapid transmission of the induced pressure head to a potential failure plane.

Groundwater ridging is the rapid rise of a shallow water table during a rainfall event, in an environment where, in the pre-event period, the capillary fringe extends to the ground surface. Groundwater ridging is widely cited to account for the observed significant appearance of pre-event water in a stream stormflow hydrograph. Various hypotheses have been advanced to explain the groundwater-ridging mechanism; and most recently, from a field study site in South Africa, an energy hypothesis was proposed, which explains that groundwater-ridging water-table rise is a result of rapid introduction and transmission of additional pressure head into the capillary fringe from an intense rainfall at the ground surface. However, there is a need for further analysis and evidence from other field study sites to confirm and support this newly proposed energy hypothesis. The objectives of this paper are, therefore, as follows: to review previous observations on groundwater ridging, from other study sites, in order to deduce evidence of the newly proposed energy hypothesis; to present and evaluate a one-dimensional diffusion mathematical model that can simulate groundwater-ridging water-table rise, based on the newly proposed energy hypothesis; and to evaluate the importance of a capillary fringe in streamflow generation. Analysis of previous observations from other study sites generally indicated that the rate of groundwater-ridging water-table rise is directly related to the rainfall intensity, hence confirming and agreeing with the newly proposed energy hypothesis. Additionally, theoretical results by the mathematical model agreed fairly well with the field results observed under natural rainfall, confirming that the rapidly rainfall-induced energy is diffusively transmitted downwards through pore water, elevating the pressure head at every depth. The results in this study also support the concept of a three-end-member stream stormflow hydrograph and contribute to the explanation of how catchments can store water for long periods but then release it rapidly during storm events. Copyright (c) 2015 John Wiley & Sons, Ltd.