Groundwater Modeling of a Deep Coastal Aquifer System in Tanzania Guided by Hydrocarbon Exploration Data

Monday, December 4, 2017: 3:30 p.m.
101 C (Music City Center)
Matthew Gamache, P.E., D.WRE , CDM Smith, Boston, MA
Henning Moe , CDM Smith, Galway, Ireland
Fridtjov Ruden , Ruden AS Geo Solutions, Engelsviken, Norway

The water authority for the city of Dar es Salaam in Tanzania initiated work to explore the water supply potential of a regional coastal aquifer system in close vicinity of the City. As part of this work, the Kimbiji Aquifer System (KAS) has been characterized to determine its capacity and suitability as a sustainable source of clean drinking water for the City. The Kimbiji Aquifer Assessment (KAA) project drilled, logged and tested 9 exploration wells ranging in depth from 1,200 to 2,000 feet, interpreted 27 seismic survey profiles spanning 710 miles from the early 1980s, and used information from four deep hydrocarbon exploration wells, one of which is offshore in the Indian Ocean, to develop a conceptual hydrogeological model of the KAS.

The conceptual model was used as the basis for numerical model development. A three-dimensional groundwater model of the aquifer system was built, calibrated and applied to examine sustainability of aquifer development alternatives (including risk of seawater intrusion) and potential environmental impacts (stream reductions, wetland depletion). The regional-scale model, which covers 4,400 mi2 (73% of which are off-shore) simulates the hydraulic interaction between fresh and saline groundwater (with the deep aquifer interface estimated to be over 10 miles offshore) as well as discharges to surface water onshore.

Based on the modeling, the estimated quantities of groundwater that can be developed in the long-term from the KAS can be as high as 70 MGD, depending on how wellfield development proceeds. Different wellfield configurations were tested with the model, which indicated that sustainable yield is more likely to be constrained by available drawdowns in production wells and other operational constraints than by seawater intrusion. For the wellfield configurations selected for further development, the groundwater model was used to examine potential protection zones, potential environmental impacts, times of travel, and groundwater age.

Slides in PDF
Matthew Gamache, P.E., D.WRE, CDM Smith, Boston, MA
Mr. Gamache is a water resources engineer who specializes in subsurface hydrologic and contaminant transport modeling. These models have been used to assess groundwater flow paths, travel times, and contaminant concentrations for litigation support, delineation of drinking water protection zones, and design of groundwater remediation systems. He received a M.S. from the University of Michigan and a B.S. from Worcester Polytechnic Institute.

Henning Moe, CDM Smith, Galway, Ireland
With 20 years of experience as a hydrogeologist, Mr. Moe's experience spans a wide range of practical applications, from village-scale groundwater development in East Africa to regional-scale water resources exploration and management in the Middle East. His primary areas of expertise are water resources planning and management, as well as the application of numerical flow and transport modeling. He has also been deeply involved in Ireland’s implementation of the EU WFD, including efforts on the national groundwater monitoring network that is being established across Ireland.

Fridtjov Ruden, Ruden AS Geo Solutions, Engelsviken, Norway

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