T: +1 (609) 947-1703
F: +1 (609) 935-0631
|
F: +1 (609) 935-0631 |
PRACTICING GEOLOGY INTERNATIONALLY - MAUN, BOTSWANA, SOUTHERN AFRICA |
||||
UHL & ASSOCIATES As so many interesting things happen, our project in Botswana was somewhat of a surprise in the way it came about from a meeting on a journey for a different purpose. During a trip to Mozambique and various other places in southern Africa in 1992, I met again after 20 years an old Kashmiri friend with whom I had once worked on a large drilling project in India. This friend, Tej Bakaya, had emigrated to Botswana in Southern Africa where he now had a consulting practice which specialized in village water supply projects. These projects were relatively small but plentiful and relied heavily on geophysics for the siting of test and production wells. Tej was looking to move into a larger local arena and we in Pennsylvania were generally looking off into the distance of foreign (subsurface saturated) soil to do something beneficial and different. The project on which we successfully bid together in March of 1995 was large and complicated and required a meeting of our respective strengths; i.e.Tej 's geophysics, pumping test team, contacts and knowledge of the country with my firm's capacity in drilling and hydrogeologic data analysis. We also contributed our very American can-do attitude and concentration on the bottom line. Our location was the town of Maun in Ngamiland in northwest Botswana. Our purpose was to explore for groundwater to supply this rapidly growing town which currently holds 30,000 inhabitants and is expected to grow to over 75,000 by 2012. The expected water demand in the year 2012 is 4 million cubic meters per year (MCM/yr.) or about 3 million gallons per day (mgd). Maun is absolutely unique situated both on the edge of the Kalahari Desert and Okavango Delta. Not often has a town been so encouraged yet so constrained by its natural environment. Water is the key to the area's internationally-acclaimed beauty and to its survival. The Okavango Delta is one of the world's largest inland river deltas. It is created by two parallel faults which serve to dam the Okavango River that spreads out into a fan-shaped pattern of perennial and semi-perennial swamps that are home to a myriad of wildlife including elephant, cape buffalo, big cats, hippo, kudu, countless small animals and birds. Maun is rapidly growing as the jumping off point for safari camps (generally reached by small chartered aircraft) in the verdant delta. At the same time, being located about 15 km southeast of the distal end of the delta. Maun is a dry dusty place most of the year where many people still spend too much time and effort hauling water. The river enters the delta at a substantial flow rate that on average is 5x106 gallons per minute (gpm) through a large channel called the Panhandle. The water leaving the delta is a trickle to this torrent, about two percent of the inflow. or about 0.1 x 106 gpm. The outflow is seasonal and the outflow channels are dry for months at a time. In recent years (1990's), the water leaving the delta flows through Mann just for a short time each year during the annual flood which occurs in the southern hemisphere winter (June-August). The photo above shows the 1996 outflow which reached the junction of the Boro and Thamalakane Rivers in early September. The 1995 and 1996 floods were the worst on record. No one knows whether this change is permanent or will reverse itself in our lifetimes.
Some of the stories we heard were strange indeed and amusing to our modem minds. One story was of a German engineer who was hired to build a small dam across one of the water channels in the Delta sometime in the early part of the century. When the dam was partially built and water was flowing fiercely through the opening, he reportedly convinced a government official that partially built dams increased the flow of water and was allowed to construct many of these monuments. Certainly a story out of another time! Although the current supply for Maun came from a wellfield (Shashe Valley), very little was known about groundwater occurrence and availability in our 5,000 square mile study area (see map). Much of this area was absolutely unexplored in terms of groundwater occurrence and availability. During the project inception period, we used all available tools and the technical expertise around us in several disciplines to synthesize a conceptual picture of the area and identify areas for exploration in the drilling program. We hired professors at the University of Botswana to study and report on vegetation, geomorphology, geological structure, surface water hydrology, and remote sensing (satellite imagery). An Australian firm conducted an airborne electromagnetic (EM) survey over a large chunk of the project area, and we conducted ground geophysical surveys. We did a reconnaissance of existing wells (called boreholes in Botswana in the British fashion). The wells we found included those for private residences and ostrich farms, for remote villages and cattle posts, in addition to the supply systems for Maun and the outlying village of Matlapaneng, which was our home (base camp) during the project.
Therefore, at the start of the exploration drilling program we were faced by several challenges. Not least was our uncertainty that we would be successful in finding sufficient overall freshwater resources, which given the hydrogeologic setting seemed a formidable task. Added to this was the need to find areas where wellfields would be feasible; i.e. where the aquifer conditions could support pumping without depletion or significant upconing of water of unacceptable quality, and would permit decent well yields. During the drilling program, we installed and pump tested about 50 exploration and test wells, many in remote areas reached by sand tracks in four-wheel drive vehicles. A number of these wells were installed in wildlife areas where encounters with elephants were not uncommon. We were very grateful to our young Botswanan scientists and technicians not just for their technical input, but for their guidance in this wild part of the planet where getting lost or stuck or making a mistake can be fatal. The discharge end of pumping test pipes encouraged locals to collect water during the three day tests (Photo 1) and on occasion, lions and other animals. The freshwater aquifers encountered in the exploration program were all similar in nature and consisted of multi-layered fine to medium sand aquifer systems with semi-confining beds of clays, sandy silts and sandy clays, overlying a brackish/saline aquifer. Test pumping in the middle semi-confined fresh water aquifers with observation wells indicated that these aquifers and confining beds are interconnected. The individual aquifers exhibited a range of hydraulic characteristics with well yields from 5 to 220 gpm. Even back at base camp, the project could never be far from our thinking. We leased a nonworking tourist camp on the banks of the Thamalakane (pronounced Tom-a-Ia-con-ee) River with thatched cottages, a kitchen and a cook, which sometimes swelled to 30 people during the busiest phases of the project. The Thamalakane River is the channel which runs through Maun and a main group of the Delta outlet channels are tributary to this river. The primary Delta outlet channel at present, the Boro River, meets the Thamalakane within walking distance of our base camp. The Thamalakane channel was dry for 10 out of 12 months per year during the project (1995 to 1997) and comprises a wide and grand pathway for parading groups of horses, wandering herds of cows and goats, villagers, children on donkeys, and certain hydrogeologists out for a stroll in the early evening. There is something slightly askew in the picture; concrete balustrades, floating docks, big motor boats sitting, that are peculiar reminders of the wet 198Os, when tourists could be ferried up into the Delta along this wide and fast flowing river. Now the boats are piled up by the side of the channel, and all of the camps including ours, are hurting for water. The project resulted in the identification of at least five areas along the river channels that could be utilized for future groundwater development for Maun into the 21st century and delineated over I 0,000 M.U. Cubic Meters (MCM) of fresh groundwater in storage. Three of these areas are located where the annual delta floods are still active. A phased development program was recommended. In addition, a successful pilot test indicated that artificial recharge basins could be used to restore the existing depleted Shashe wellfield during the annual flood in nearby channels, if wetter conditions return and sufficient surface water were to be available. In the long term, the sustainability of the water resource will depend on continued recharge to these aquifer systems from the annual flood from the Delta. The volume of these flood waters as well as the preservation of the Delta itself will require international cooperation. Already, plans by Namibia to divert water from upstream points of the Okavango River to it's capital city area (Windhoek) are undergoing intense scrutiny by interested parties in Botswana. How these issues are resolved in conjunction with the naturally shifting hydrology in this area will determine its future. Although, we finished up the 2-year project and headed home due to domestic obligations, we look forward to practicing again at some future time in this lovely and interesting county. This project was the largest groundwater contract to date awarded by the Government of Botswana, and was the first time an American firm was selected. As newcomers to Maun, we very quickly attracted attention as the water people who were consulted by various entrepreneurs, tour operators, people passing through with various missions like the energetic lady from Vermont who was determined to start a school, the Australian Broadcasting Corporation reporters who were interested in potential impacts from proposed upstream Namibian diversions from the Okavango River, and others who were just friendly and curious. We would love to return. |
||||
| CONTACT US |
|
|||
|
||||
The groundwater exploration project for Maun's water supply was initiated by our client, the Department of Water Affairs of the Government of Botswana. This project followed on the heels of large-scale engineering schemes proposed by a large engineering firm working for the Department of Water Affairs for the region, which entailed dredging, dams and reservoirs. These schemes were judged faulty by the International Union for the Conservation of Nature (IUCN) review team, who recommended that the conjunctive use of surface water and groundwater be examined. Local conservationist organizations and residents also assisted in defeating these schemes which were contemplated with much consternation because of their extensive disturbance to the natural environment. During our time in Maun, we naturally heard much local lore and many colorful stories. Not least of these were stories of attempts to change or clear the water channels of the delta which purportedly always ended in failure. The moral of the story was not to try to force changes, the consequences of which could not be understood or predicted, and which would undoubtedly be ill-fated. Groundwater was a possible and benign alternative.
