Jonathan Levy

The impact of storm events on a riverbed system and its hydraulic conductivity at a site of induced infiltration

The spatial and temporal variability of riverbed vertical hydraulic conductivity (K(v)) was investigated at a site of induced infiltration, associated with a municipal well field, to assess the impact of high-stage events on scour and subsequently the riverbed K(v). Such impacts are important when considering the potential loss of riverbank filtration capacity due to storm events. The study site, in and along the Great Miami River in southwest Ohio, overlaid a highly productive glacial-outwash aquifer. A three-layer model for this system was conceptualized: a top layer of transient sediment, a second layer comprising large sediment resistant to scour, but clogged with finer sediment (the armor/colmation layer), and a third layer that was transitional to the underlying higher-K(v) aquifer. One location was studied in detail to confirm and quantify the conceptual model. Methods included seepage meters, heat-flow modeling, grain-size analyses, laboratory permeameter tests, slug tests and the use of scour chains and pressure-load cells to directly measure the amount of sediment scour and re-deposition. Seepage meter measured riverbed K(v) ranged from 0.017 to 1.7 m/d with a geometric mean of 0.19 m/d. Heat-transport model-calibrated estimates were even lower, ranging from 0.0061 to 0.046 m/d with a mean of 0.017 m/d. The relatively low K(v) was indicative of the clogged armor layer. In contrast, slug tests in the underlying riverbed sediment yielded K(v) values an order of magnitude greater. There was a linear relationship between scour chain measured scour and event intensity with a maximum scour of only 0.098 m. Load-cell pressure sensor data over a 7-month period indicated a total sediment-height fluctuation of 0.42 m and a maximum storm-event scour of 0.28 m. Scour data indicated that the assumed armor/colmation layer almost always remained intact. Based on measured layer conductivities and thicknesses, the overall K(v) of this conceptualized system was 1.6 m/d. Sensitivity analyses indicated that even complete scour of the armor/colmation layer would likely increase the overall K(v) only by a factor of 1.5. Most scour events observed removed only the transient sediment, having very little effect on the entire system indicating low risk of losing filtration capacity during storms. The research, however, focused on the point bar, depositional side of the river. More research of the entire river profile is necessary.

Review: Groundwater management and groundwater/surface-water interaction in the context of South African water policy

Groundwater/surface-water interaction is receiving increasing focus in Africa due to its importance to ecologic systems and sustainability. In South Africa’s 1998 National Water Act (NWA), water-use licenses, including groundwater, are granted only after defining the Reserve, the amount of water needed to supply basic human needs and preserve some ecological integrity. Accurate quantification of groundwater contributions to ecosystems for successful implementation of the NWA proves challenging; many of South Africa’s aquifers are in heterogeneous and anisotropic fractured-rock settings. This paper reviews the current conceptualizations and investigative approaches regarding groundwater/surface-water interactions in the context of South African policies. Some selected pitfall experiences are emphasized. The most common approach in South Africa is estimation of average annual fluxes at the scale of fourth-order catchments (∼500 km2) with baseflow separation techniques and then subtracting the groundwater discharge rate from the recharge rate. This approach might be a good start, but it ignores spatial and temporal variability, potentially missing local impacts associated with production-well placement. As South Africa’s NWA has already been emulated in many countries including Zambia, Zimbabwe and Kenya, the successes and failures of the South African experience dealing with the groundwater/surface-water interaction will be analyzed to guide future policy directions.RésuméL’interaction eau souterraine/eau de surface est un centre d’intérêt croissant en Afrique étant donné son importance pour les systèmes écologiques et leur pérennité. Dans le National Water Act sud-africain de 1998 (NWA), des autorisations d’utilisation de l’eau, incluant l’eau souterraine, sont accordées seulement après évaluation de la Réserve, de la quantité d’eau requise pour satisfaire les besoins humains essentiels et préserver une certaine intégrité écologique. Une évaluation précise des contributions de l’eau souterraine aux écosystèmes pour la mise en œuvre du NWA s’avère être un défi; beaucoup d’aquifères d’Afrique du Sud sont dans des encaissants rocheux fracturés hétérogènes et anisotropes. Cet article passe en revue les concepts et approches actuels des interactions eau souterraine/eau de surface dans le contexte des politiques d’Afrique du Sud. Certaines expériences piège sélectionnées sont mises en évidence. L’approche la plus commune en Afrique du Sud est l’estimation des flux annuels moyens à l’échelle des bassins versants du quatrième ordre (∼500 km2) avec des techniques de séparation du débit de base, puis de soustraction des taux de décharge et de recharge. Cette approche pourrait être un bon début, mais elle ignore la variabilité spatiale et temporelle, éludant potentiellement les impacts locaux associés à la localisation des puits de production. Comme le NWA d’Afrique du Sud a déjà fait des émules dans de nombreux pays dont la Zambie, le Zimbabwe et le Kenya, les succès et les échecs de l’expérience sud-africaine concernant l’interaction eau souterraine/eau de surface seront analysés pour guider les orientations de la politique future.ResumenLa interacción agua subterránea/agua superficial está recibiendo una creciente atención en África debido a su importancia en los sistema ecológicos y su sustentabilidad. En Sudáfrica, según la Ley Nacional de Agua (NWA) de 1998, las licencias de uso del agua, incluidas las aguas subterráneas, sólo se conceden después de definir la Reserva, que es la cantidad de agua necesaria para abastecer las necesidades humanas básicas y para preservar la integridad ecológica. La cuantificación precisa de la contribución del agua subterránea a los ecosistemas para la implementación exitosa de la NWA resulta difícil, ya que muchos de los acuíferos de Sudáfrica presentan la configuración heterogénea y anisotrópica en rocas fracturadas. En este documento se realiza un revisión de los conceptos y enfoques actuales de la investigación de la interacción aguas subterráneas/aguas superficiales en el contexto de las políticas de Sudáfrica. Se destacan algunas experiencias seleccionadas con las dificultades encontradas. El enfoque más común en Sudáfrica es la estimación de los flujos anuales promedio en cuencas de drenaje de cuarto orden (∼500 km2) utilizando las técnicas de separación del flujo de base y luego restando la tasa de descarga del agua subterránea a la tasa de recarga. Este enfoque podría ser un buen comienzo, pero no tiene en cuenta la variabilidad espacial y temporal, faltando los impactos locales asociados a la ubicación de los pozos de producción. Como la NWA de Sudáfrica ha sido emulada en muchos países, incluyendo Zambia, Zimbabwe, Kenia, los éxitos y fracasos de la experiencia de Sudáfrica sobre la interacción aguas subterráneas/aguas superficiales deberán ser analizados para guiar las futuras orientaciones políticas.ResumoA interacção água subterrânea/água superficial recebe cada vez maior atenção em África, devido à sua importância para os sistemas ecológicos e para a sustentabilidade. Na África do Sul, no Acto Nacional da Água (NWA) de 1998, as licenças de uso da água, incluindo a água subterrânea, são garantidas apenas depois de definidas as Reservas, a quantidade de água necessária para suprimir as necessidades humanas básicas e a preservação de alguma integridade ecológica. A quantificação acurada das contribuições da água subterrânea para os ecossistemas para uma aplicação com sucesso da implementação do NWA provou-se ser desafiadora; muitos dos aquíferos situam-se em meios heterogéneos e anisotrópicos, em rochas fracturadas. Este documento revê a conceptualização corrente e os processos de investigação que têm sido aplicados às interacções águas subterrâneas/águas superficiais no contexto das políticas Sul-Africanas. Algumas experiências seleccionadas são enfatizadas. A aproximação mais comum na Áfria do Sul é a estimação dos fluxos anuais médios à escala da bacia de quarta ordem (∼500 km2), utilizando técnicas de separação do fluxo de base e subtraindo então a descarga subterrânea da taxa de recarga. Esta aproximação pode ser um bom começo, mas ignora a variabilidade espacial e temporal, negligenciando potencialmente os impactes locais associados à exploração de campos de captações. Como o NWA Sul-Africano já foi emulado por muitos outros países, incluindo a Zâmbia, o Zimbabué e o Quénia, os sucessos e insucessos da experiência Sul-Africana ao lidar com as interacções águas subterrâneas/águas superficiais serão analisadas, para guiar as direcções políticas futuras.

Sorption-desorption of carbamazepine by palygorskite-montmorillonite (PM) filter medium.

Palygorskite-montmorillonite (PM) was studied as a potential sewage treatment effluent filter material for carbamazepine. Batch sorption experiments were conducted as a function of granule size (0.3-0.6, 1.7-2.0 and 2.8mm) and different sewage effluent conditions (pH, ionic strength and temperature). Results showed PM had a mix of fibrous and plate-like morphologies. Sorption and desorption isotherms were fitted to the Freundlich model. Sorption is granule size-dependent and the medium granule size would be an appropriate size for optimizing both flow and carbamazepine retention. Highest and lowest sorption capacities corresponded to the smallest and the largest granule sizes, respectively. The lowest and the highest equilibrium aqueous (Ce) and sorbed (qe) carbamazepine concentrations were 0.4 mg L(-1) and 4.5 mg L(-1), and 0.6 mg kg(-1) and 411.8 mg kg(-1), respectively. Observed higher relative sorption at elevated concentrations with a Freundlich exponent greater than one, indicated cooperative sorption. The sorption-desorption hysteresis (isotherm non-singularity) indicated irreversible sorption. Higher sorption observed at higher rather than at lower ionic strength conditions is likely due to a salting-out effect. Negative free energy and the inverse sorption capacity-temperature relationship indicated the carbamazepine sorption process was favorable or spontaneous. Solution pH had little effect on sorption.

Assessing ground water development potential using Landsat imagery.

Seven villages in southeastern Kenya surround Mt. Kasigau and depend on the mountains cloud forest for their water supply. Five of these villages have regularly experienced water shortages, and all village water supplies were contaminated with Escherichia coli bacteria. There is a need to economically find new sources of fresh ground water. Remote sensing offers a relatively quick and cost-effective way of identifying areas with high potential for ground water development. This study used spectral properties of features on Landsat remote sensing imagery to map linear features, soil types, surface moisture, and vegetation. Linear features represented geologic or geomorphologic features indicating either shallow ground water or areas of increased subsurface hydraulic conductivity. Regarding soil type, black soils were identified as potential indicators of shallow aquifers based on their relatively lower elevation and association with river valleys. A vegetation map was created using unsupervised classification, and three of the resulting vegetation classes were observed to be commonly associated with wet areas and/or ground water discharge. A wetness map, created using tasseled cap analysis, was used to identify all areas of high ground moisture, including those that corresponded to vegetated areas. The linear features, soil type, vegetation, and wetness maps were overlaid to produce a composite that highlighted areas with the highest potential for ground water development. Electrical resistivity surveys confirmed that areas highlighted by the composite image had relatively shallow depths to the water table. Some figures in this paper are available in color in the online version of the paper.

Drinking water quality in the Mount Kasigau region of Kenya: a source to point-of-use assessment

Drinking water quality was investigated in seven rural villages surrounding Mount Kasigau in southeastern Kenya, where water is piped from unprotected dammed streams and springs in the Kasigau cloud forest down to taps, kiosks, and tanks in the villages. Analyses were conducted for nutrients, trace metals, and pathogen indicators in water from community taps, water stored in homes, and collection points along the pipelines up to catchment dams on the mountain. Water was relatively free from nutrient and trace-metal contamination; however, all samples were contaminated with total coliforms and nearly all were contaminated with Escherichia coli. There was no discernable pattern in the extent of contamination from the catchment dams to the villages. In each of three villages chosen for further study, six residents were selected for a more in-depth investigation. Water quality was generally worse in water stored in those homes compared to water collected at the village taps. The quality of drinking water in homes where treatment was applied was no better than in homes with no water treatment. The Kasigau villages, as many other areas in the developing world, need inexpensive and effective water treatment, as well as an assessment of the effectiveness of sanitary and hygienic practices.