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Hydrogeological characteristics of the Omaruru Delta Aquifer System in Namibia

  • Brian Matengu
  • Yongxin XuEmail author
  • Eric Tordiffe
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  • 34 Downloads

Abstract

Sustainable utilization of groundwater in parts of hyper-arid Sub-Saharan Africa, like the Namib Desert, is always a challenge due to lack of resources and data. For the Omdel Aquifer in the Omaruru catchment, Namibia, issues to investigate include the lack of information on the geology and hydrogeological setting, the hydraulic properties and geometry of the aquifer at the inflow and outflow sections, groundwater recharge conditions upstream of the aquifer, and the impact of artificial recharge. In this desert environment, the methods applied are hydrogeological surveys and site visits, together with interpretation of geological, hydrological and geomorphological data from investigations carried out to define the hydrogeological characteristics of the Omdel Aquifer. The bedrock geometry of the aquifer indicates that the Main channel (one of four palaeochannels) is the largest reservoir of stored fresh groundwater, estimated at 133 Mm3, and it is deeper than the other three channels, with an average sediment thickness of 80 m. All groundwater chemistry facies of the selected boreholes tapping the Omdel Aquifer reveal a NaCl character, indicating a coastal environment. The yield of the Omdel Aquifer is estimated to have increased from 2.8 Mm3/year before construction of a recharge enhancement dam to 4.6 Mm3/year after the construction. This paper focuses on the understanding of hydrogeological characteristics of the Omaruru Delta Aquifer System in terms of groundwater recharge and discharge, groundwater dynamics within the aquifer and groundwater chemistry, in order to assess whether the current abstractions are operating within the hydrogeological limits of sustainability.

Keywords

Hydrogeological characteristics Artificial recharge Coastal aquifer Sub-Saharan Africa Namibia 

Caractéristiques hydrogéologiques du système aquifère du delta d’Omaruru en Namibie

Résumé

L’utilisation durable des eaux souterraines dans les régions de l’Afrique Sub-Saharienne hyper-aride, comme le désert du Namib, est toujours un défi dû au manque de ressources et de données. Pour l’aquifère d’Omdel dans le bassin d’Omaruru, en Namibie, les sujets à étudier incluent l’absence d’information sur le contexte géologique et hydrogéologique, les propriétés hydrauliques et géométriques de la couche aquifère à l’entrée et à la sortie du système, les conditions de recharge des eaux souterraines en amont de l’aquifère, et l’impact de la recharge artificielle. Dans cet environnement désertique, les méthodes appliquées sont des campagnes hydrogéologiques et des visites de terrain, ainsi que l’interprétation des données géologiques, hydrologiques et géomorphologiques à partir des investigations effectuées pour définir les caractéristiques hydrogéologiques de l’aquifère d’Omdel. La géométrie du substratum de l’aquifère indique que le chenal principal (l’un des quatre paléochenaux) est le plus grand réservoir d’eaux douces souterraines, estimé à 133 Millions de m3, et plus profond que les trois autres chenaux, avec une épaisseur moyenne de sédiments de 80 m. Tous les faciès chimiques des eaux souterraines des forages sélectionnés captant l’aquifère d’Omdel traduisent un caractère chloruré sodique indiquant un environnement côtier. On estime que le rendement de l’aquifère d’Omdel a augmenté de 2.8Mm3/an avant la construction d’un barrage pour améliorer la recharge à 4.6 Mm3/an après sa construction. Cet article se concentre sur la compréhension des caractéristiques hydrogéologiques du système aquifère du delta d’Omaruru en termes de recharge et décharge d’eaux souterraines, la dynamique des eaux souterraines dans l’aquifère et la chimie des eaux souterraines, afin d’évaluer si les conditions d’exploitation actuelles opèrent dans les limites hydrogéologiques de durabilité.

Características hidrogeológicas del sistema de acuíferos del delta de Omaruru en Namibia

Resumen

La utilización sostenible del agua subterránea en zonas hiperáridas del África subsahariana, como el desierto de Namib, es siempre un desafío debido a la falta de recursos y de datos. Para el acuífero Omdel en la cuenca de Omaruru, Namibia, los problemas que se investigan incluyen la falta de información sobre el ambiente geológico e hidrogeológico, las propiedades hidráulicas y la geometría del acuífero en las secciones de entrada y salida, las condiciones de recarga del agua subterránea aguas arriba del acuífero y el impacto de la recarga artificial. En este ambiente desértico, los métodos aplicados son los estudios hidrogeológicos y los relevamientos en los sitios, junto con la interpretación de los datos geológicos, hidrológicos y geomorfológicos de las investigaciones realizadas para definir las características hidrogeológicas del acuífero Omdel. La geometría del basamento del acuífero indica que el canal Principal (uno de los cuatro paleocanales) es el reservorio más grande de agua subterránea dulce almacenada, que se estima en 133 Mm3, y es más profundo que los otros tres canales, con un espesor de sedimento promedio de 80 m. Todas las facies de química del agua subterránea de los pozos seleccionados que alcanzan el Acuífero Omdel revelan un carácter de NaCl, lo cual indica un ambiente costero. Se estima que el rendimiento del Acuífero Omdel aumentó la recarga de 2.8 Mm3/año antes de la construcción de una represa a 4.6 Mm3/año después de la construcción. Este trabajo se enfoca en la comprensión de las características hidrogeológicas del Sistema de Acuíferos del Delta de Omaruru en términos de recarga y descarga, dinámica del acuífero y química del agua subterránea, para evaluar si las extracciones actuales están operando dentro de los límites hidrogeológicos de la sostenibilidad.

纳米比亚奥马鲁鲁三角洲含水层系统的水文地质特征

摘要

由于缺乏资源和数据,过度干旱的撒哈拉以南非洲部分地区如纳米布沙漠地下水的可持续利用一直是一个挑战。对于纳米比亚奥马鲁鲁流域的Omdel含水层,调查中的问题包括缺乏地质和水文地质背景信息、流入和流出剖面处含水层的水力特性及几何结构、含水层上游的地下水补给条件以及人工补给的影响。在这个沙漠环境中,应用的方法为水文地质调查、现场查看、以及进行调查中获取的地质、水文和地貌数据的解译,以确定Omdel含水层的水文地质特征。含水层的基岩几何结构表明,主要通道(四个古通道之一)是最大的储存地下淡水的储存地,该储存地估计为133 Mm3,这个通道比其它三个通道都要深,平均沉积厚度为80 m。所选择的Omdel含水层钻孔所有地下水化学相都显示为NaCl,表明这里是为沿海环境。Omdel含水层出水量估计从增大补给大坝建设前的2.8 Mm3/年增加到建设后的4.6 Mm3/年。本文重点就是了解奥马鲁鲁三角洲含水层系统地下水补给和排泄、含水层之内的动力学以及地下水化学等水文地质特征,以评价目前的开采是否在可持续的水文地质范围内运行。

Características hidrogeológicas do Sistema Aquífero Delta Omaruru, Namíbia

Resumo

A utilização sustentável de água subterrânea em partes hiperáridas da África Sub-Sahariana, como no deserto da Namíbia, é sempre um desafio devido à escassez de recursos e dados. Para o Aquífero Omdel na bacia de Omaruru, Namíbia, os problemas de investigação incluem a falta de informações geológicas e de aspectos hidrogeológicos, das propriedades hidráulicas e da geometria do aquífero nas seções de infiltração e escoamento, das condições de recarga das águas subterrâneas a montante do aquífero e dos impactos de recargas artificiais. Neste ambiente desértico, os métodos aplicados são pesquisas hidrogeológicas e visitas de campo, juntamente às interpretações dos dados geológicos, hidrogeológicos e geomorfológicos utilizadas para definir as características hidrogeológicas do Aquífero Omdel. A geometria da rocha matriz que aporta o aquífero indica que o canal principal (um de quatro paleocanais) é o maior reservatório em armazenamento de águas subterrâneas, estimado em 133 Mm3, e este é o mais profundo em relação aos outros três canais, com uma espessura média de sedimentos de 80 m. Todas as fácies hidroquímicas das águas subterrâneas dos poços exploratórios do Aquífero Omdel revelam um carácter NaCl, o qual indica um ambiente costeiro. É estimado um aumento da produtividade do Aquífero Omdel com a construção da barragem para melhoramento da recarga, com valores antes da construção de 2.8 Mm3/ano chegando a 4.6 Mm3/ano após a construção. Este artigo possui foco no entendimento das características hidrogeológicas do Sistema Aquífero Delta Omaruru em termos de recarga e descarga, dinâmica e hidroquímica das águas subterrâneas, a fim de avaliar se as retiradas atuais estão operando dentro dos limites de sustentabilidade hidrogeológica.

Notes

Acknowledgements

The authors acknowledge Namibia Water Corporation Ltd., Geohydrology and Hydrology divisions in the Department of Water Affairs and Forestry, Namibia, for their data, and the Namibia Meteorological Services for the historic rainfall data. The valuable comments and suggestions from the two reviewers are highly appreciated.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Earth SciencesUniversity of the Western CapeCape TownSouth Africa
  2. 2.Namibia Water Corporation LtdWindhoekNamibia
  3. 3.Institute of African Water Resources and EnvironmentHebei University of EngineeringHebeiChina
  4. 4.Karst Hydrogeological ConsultantsWindhoekNamibia

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