WDjOsj81j30 December 1981

Report on a visit to Malawi, November 1981.

by

E P Wright.

REPORT ON A VISIT TO MALAWI, NOVEMBER 1981. Dr E P Wright, Hydrogeological Adviser to ODA.

1. DIARY

November 18th

November 19th-23rd

November 24th

November 25th-26th

November 27th-30th

November 30th

2. OBJECTIVES

Arrived Lilongwe

Discussions in Lilongwe in Department of Lands, Valuation and water; also with Mr J Doughty of the Ministry of Agriculture in connection with the Lower Shire.

Field visit to Livulezi Project Area with Mr J Chilton and Mr D R C Grey of the ODA Project Team.

Visit to Lower Shire Valley with Dr K A Edwards, Chief water Resources Officer and Mr ~ Chilton. Discussions with Mr J H Staal, Hydrogeologist of the Shire Valley Agricultural Consolidation Project and also with the Programme Manager; short field visit to drilling site.

Lilongwe. Discussions included one with Mr J W Hodges, Engineering Adviser in the Development Division.

Lilongwe - Nairobi.

2.1 The main purpose of the visit was to review the progress of the ODA Groundwater Project and to discuss the programme of work for the final year of the Project (1982). At the request of Dr Edwards, Chief water Resources Officer, a short visit was made to the Lower Shire and a preliminary programme formulated for additional in­vestigations of the groundwater resources (Appendix I).

3. BACKGROUND SUMMARY

3.1 The ODA Groundwater Project commenced in December 1979 and two hydrogeologists from IGS were assigned (Mr P J Chilton and Mr D R C Grey). A third hydrogeologist (Miss A Smith--Carington) will be joining the Team in late December 1981 and all three will remain in Malawi until termination of the Project in December 1982.

3.2 The ODA Team commenced operations at the same time as control of groundwater exploration and development was transferred from the Ministry of Mines to the newly formed Department of Lands, Valuation and Water. A number of geologists/technicians in the Geological Survey including the whole of Drilling Section were transferred to

this Department. The ODA Team has taken over virtual control of the Groundwater Section in the Department under the overall respon­sibility of the Chief Water Resources Officer. Significant modifica­tions in methodology and in development policy have been initiated and some of the innovations introduced are worthy of consideration in countries other than Malawi where similar conditions and require­ments exist.

4. PROGRAMME OF WORK

4.1 The main items of the work programme are listed below and brief comments on current progress. More detailed information on some of these topics is provided elsewhere in this Report.

(a) Integrated Projects.

The main current concern of the aDA Team. Following the success of the feasibility study a pilot project has commenced in the Livulezi Valley. Notable features include important changes in well siting, drilling, completion and design; also in respect to the financial support which has sources which include central government as well as a variety of external donors.

Tactical research requirements include the use of rapid reconnaissance geophysical techniques, notably electromagnetic, and the evaluation of overall groundwater resource availability for development in the long term context.

(b) Master Plan.

Limited inputs required on data assemblage for the first Phase. Recommended that resource evaluation studies for one or two selected Units should be prepared.

(c) Urban Supply.

Little advance on previous knowledge but some analytical studies carried out in UK on collector well application in the weathered base­ment aquifer. Agreed that analytical studies will continue and consideration given to setting up pilot investigation in Malawi.

(d) Groundwater Potential for Irrigation.

Limited project input planned mainly in the analysis of pumping tests at selective drilled sites in the alluvial basins. Data will also be forwarded to UK for additional examination.

(e) Borehole Maintenance.

(f) Water Quality.

The geochemist, Mr J Lewis, has now been appointed, and work is pro­ceeding in the setting up of a laboratory. It is hoped to initiate basic studies on various geochemical problems.

5. DISCUSSION

5.1 Integrated Project for Rural Groundwater Supply.

Two Documents prepared by the team are enclosed with this Report.

(a) Rural Groundwater Supply: An Alternative Strategy

(b) Upper Livulezi: Integrated Project Document

Document (a) outlines the strategy and describes the results of the preliminary feasibility study in the Livulezi Valley. Document (b) outlines the project planning for the first pilot development scheme which has now commenced and is scheduled to be completed over 18 months with a subsequent 3-year maintenance phase. A second scheme is planned to commence in early 1982 and if circumstances (mainly staff availability and finance) permit a third scheme will commence before the end of 1982.

5.1.1 Certain inherent implications of this new approach lnerit comment. The concept is administratively and technically very efficient and from the viewpoint of the requirements of the country as a whole, the method should result in a much more rapid and effective develop­ment of rural groundwater than would the piecemeal approach that has been standard hitherto. It does mean however that local priorities are only catered for either in the context of a general priority for the region or on the basis of a separate assignment which has to be given a very high rating in order to be incorporated into the main scheduled programme of work.

5.1.2 It must be recognised that it is only by means of this integrated and concentrated approach that Malawi has any likelihood of meeting its 'Decade' target for rural water supply development. There is also a requirement of very significant inputs, both technical and financial, if this projected planning is to be implemented.

5.1.3 The writer has a few comments on points of detail. In view of the scale and complexity of the project finances, it would seem desirable that proper assistance is provided to the Groundwater Section on the financial and accountancy procedures. It would also seem worth­while to apply realistic costings to all phases of these development schemes so that cost benefit analysis is feasible.

5.1.4 On more technical aspects, it seems to the writer that constant re­appraisal is needed of the effectiveness of the limited site inves­tigation procedures. Consideration could be given to the use of reconnaissance geophysical techniques, notably electromagnetic, to provide general control of the bedrock topography in a project area or for more local site investigations where this feature is likely to be critical. A comment on the usefulness of the EM technique in this context has been requested from Mr Carruthers of the Applied Geophysics Unit.

5.1.5 The initial development schemes, Livulezi and Bua, could usefully be expanded to include more basic studies on groundwater occurrence and resources. The information would be of value both locally and by extrapolation elsewhere, and in the context of the Regional Resource Unit studies. Aspects requiring such basic studies include climatology (a temporary station could be set up at a central base camp) i rainfall-runoff correlations and baseflowi

recharge evaluation by water level changes in a hydrometric network and possibly using geochemical techniques (chloride content of rain­fall and infiltration moisture); a detailed study of the role of the dambo in the hydrological cycle; significant hydrochemistry.

5.2 Groundwater Potential for Urban Use.

5.2.1 Little advance has been made during the current year on this topic. The weathered basement aquifer which is widespread throughout Malawi has generally a low permeability which is adequate for low produc­tion wells fitted with hand pumps «1 litre/sec). A high discharge from a motorised pump (say 3 litres/sec upwards) could not be sus­tained on account of the large drawdown which must result. Locally the weathered surface aquifer has higher permeability (or more prob­ably higher transmissivity) and can tolerate these higher abstrac­tion rates. The higher transmissivity is probably associated with thicker weathering profiles (> 30 m) and is not necessarily in­dicative of significantly higher permeability. The occurrence of thick weathering profiles are variously ascribed to favourable mineralogical composition (high mica content) or grain size characteristics (fine grain) in the fresh bedrock, or to localised tectonic fracturing which may sometimes be associated with dyke intrusion. The mechanisms for producing deep weathering profiles are not completely understood but in a recent study in Nigeria (Ackworth, unpublished Ph.D. Thesis, Birmingham, 1981) it is stated that such deep weathering tends to be localised in discontinuous and narrow «1 km) troughs.

5.2.2 Geophysical techniques are most able to identify such deep weathering troughs with electrical resistivity the most convenient and applic­able method. Lateral variations in surface resistivity are common and fairly elaborate methods (e.g. the resistivity profile section method) are needed to overcome the effects and obtain proper corre­lation. The general economics of the investigation need to be favourable to merit a detailed geophysical study on this scale, with of course no guarantee of success. Further studies are needed on the occurrence of deep weathering troughs in Malawi in the hope of being able to identify them, at least in preliminary fashion, by one or other of the rapid reconnaiss.ance techniques such as remote sensing, electromagnetic traversing, topographic association, relation to palaeosurfaces etc. The studies should include further consideration of the actual weathering processes, both above and below the water table.

5.2.3 A second factor, namely recharge r becomes more critical when high localised abstraction is a possibility. In view of the probable lateral discontinuity of the deep weathering troughs, effective discharge must be also localised and this constraint could have a significant effect on resource availability. Typical heavy surface clays will have poor infiltration capacity unless fully penetrative cracks develop during the dry season. Laterites too seem likely to have poor infiltration rates. Ackworth (op.cit) considers that recharge will only be significant if recent erosion has stripped off, either areally or along drainage lines, the uppermost layers, mainly clays and laterites) of the weathering profile.

5.2.4 It can be readily demonstrated that 'high' capacity wells (3 l/sec+) are only feasible if such wells are sited in deep weathering troughs. The advantage of the large diameter dug well in the typical weathered surface aquifer is the high storage which offsets the low perme­ability. Even so, the diameter of the dug well must be very large indeed to permit periodic abstraction of this order. Apart from the labour involved, large diameter dug wells are almost impossible to 'protect' from pollution. One possible well design which would have the attributes of a large diameter well without the disadvant­ages referred to is a • collector , well in which a number of narrow diameter laterals are drilled radially from a central shaft (Ranney Well). Such wells are normally used in thin laterally extensive aquifers of high permeability and high effective recharge. Typical locations are in river gravels with recharge induced from the surface flows. The high cost of constructing the Ranney Well has to date precluded their use in other circumstances than those described above.

5.2.5 The possibility of using the Ranney Well in a weathered basement aquifer is perhaps worth consideration if it allows sustained high abstraction. The high value of water for urban use will permit relatively high construction costs and it should be noted that many of the towns and large villages in Malawi are situated where surface sources are generally unavailable other than at high cost, e.g. long distance piped supply. Preliminary calculations for a Ranney Well system in a typical basement aquifer indicates (Appendix 11) that shallow drawdowns can be sustained at prduction rates of 3-6 litres/sec. These results indicate that a Ranney well is tech­nically feasible to produce sustained rates suitable for development by motorised pump. The cost feasibility has yet to be evaluated and a further report on this aspect includino the practicalities of construction will be presented shortly. Consideration can then be given to carrying out a pilot experimental study.

5.3 Master Plan.

This project is in its first year and the Project Leader has been appointed comparatively recently. The Groundwater Section will, it is assumed, provide the essential data for the groundwater com­ponent of the Master Plan and this input will need to be co-ordinated with the latter's programme. Some preparation based on assumed requirements has been completed. All data records are now available on CARDEX cards. Although the CARDEX system could be readily transferred to a computerised data storage and retrieval system, it is questionable whether the work should be accorded high priority in the context of the present programme of work of the Groundwater Section and the staff available.

5.3.1 The Groundwater Section also plans to provide proposals for a de­velopment strategy and to this end, it is hoped that at least two of the Resource Units can be reported upon by the end of 1982. Although these regional resource evaluation studies are being accorded a fairly low priority in comparison with the develo~ment projects, there is merit in attempting to complete at least two units during the present phase of the Master Plan Programme. The assessments will indicate more precisely the extent of information available as a basis for the formulation of the Master Plan.

5.4 Research.

Development projects are currently of over-riding priority in Malawi and there seems clear justification for this approach. It would be a mistake however to ignore all research considerations since the results of properly designed and directed programmes of work could prove of great value. It should be recognised that it is often feasible to incorporate research studies into current develop­ment programmes at comparatively modest cost as compared with that for setting up a specific independent study.

5.4.1 Particular topics considered of current importance are listed below and can readily be incorporated into present programmes.

(a) Recharge to the weathered basement aquifer. Studies could range from more broad-based regional considerations (remote sensing of land terrain with seasonal effects, base flow analysis, regional water balance calculations) to more detailed localised studies (piezometric net and water level changes, water chemistry and moisture content/potential in selected profiles) .

(b) Pollution hazards in the weathered basement aquifer. The topic is of great significance in view of the increasing emphasis on developing the shallower levels in the aquifer, whether by shallow boreholes or 'protected' hand dug wells. Surveys and monitoring programmes are obvious methods to adopt.

(c) The feasibility of designing high capacity wells in the basement complex (see above). Such wells would be of value for urban supply or irrigation.

(d) Groundwater Hydrochemistry. (i) Basement aquifers tend to have good quality groundwaters reflecting the rapid throughput in the hydrological cycle. Records do indicate the local occurrence of undesirable levels of particular constituents and iron is perhaps the most important of these. The reason for such high iron contents in basement groundwater is not known and could relate to well design or to conditions within the aquifer. The information is needed since it could indicate the most effective way of avoiding the condition or alternatively, could demonstrate that treatment was unavoidable. (ii) Alluvial aquifers. The potential of alluvial aquifers for irrigation use is under current consideration and a major constraint to development could be water quality, as for example in the Lower Shire Valley. Detailed studies are needed to evaluate the occurrence and causes of the saline water distribution.

5.5 The Use of Geophysical Techniques.

A Report on the use of geophysical techniques in groundwater ex­ploration in Malawi has been written by R M Carruthers of IGS, based on the results of a visit between October-December 1980. A detailed comment on this Report is not appropriate here but two particular points seem worthwhile emphaSising in relation to the present programme of work.

(a) The use of electromagnetic equipment has been recommended for reconnaissance investigations of the depth to bedrock. The most appropriate equipment would seem to be the Geonics EM 34-3 and consideration should be given to purchasing this. The present price is about £5500.

(b) The use of resistivity for detailed evaluation of the geometry of a deep weathering trough and some delimitation of the individual weathering units. A study of this nature would be appropriate only where high capacity well sites were being sought. The use of the profile section technique (Ackworth, op. cit) could be considered. The ABEM Terrameter with booster would be required. A further comment on these two more specific proposals is to be requested from Mr Carruthers.

5.6 Hand Pumps.

Abstraction of groundwater in rural areas of Malawi is carried out almost wholly by hand pumps which therefore represent a major in­vestment. Factors including capital cost, efficiency, ease of installation, use and maintenance and general robustness are crucial and all the existing hand pumps in use in Malawi show various deficiencies in one or other of these criteria. In view of the critical importance of the hand pump and in the context of the current emphasis on 'protected' hand dug wells and boreholes drilled to minimum depths, the Groundwater Section is in process of developing a hand pump best suited to conditions in Malawi. The prototype design which is currently in operation in some 25 boreholes combines some of the best features of the Consallen and India Mk II Hand Pumps, both of which were given a high rating in the recent ODA/Consumer Association Test Review. Additional modifications are expected to be introduced after this initial period of field use and it would also be desirable if the Malawi Pump could be given a thorough test in the Consumers' Association Hand Pump Testing Laboratory in the UK. A request that this should be done under UK aid terms is to be expected shortly via the High Commission.

5.7 Action Required.

1. Despatch of Malawi Hand Pump to the Consumers Association for testing - pending ODA agreement to fund.

2. Report on the methodology of construction of a Ranney Collector well with particular reference to conditions in the weathered basement aquifer of Malawi. By E P WRIGHT

3. Comments by Mr R Carruthers, Applied Geophysics Unit, with specific reference to reconnaissance profiling by electro­magnetic technique and to detailed evaluation of geometry/ lithology of a deep weathering trough by electrical conductivity

4. Continued desk studies on occurrence of iron in basement aquifer ground waters. By Dr A H BATH.

E P Wright 4 January 1982

Appendix I

NOTE ON THE PROGRAMME FOR INVESTIGATING THE GROUNDWATER RESOURCES IN THE LOWER SHIRE VALLEY.

1. The following note provides a broad assessment of the requirements for further work in groundwater in the Lower Shire Valley. It follows discussions with Mr J H Staal, Hydrogeologist of the Ngabu Agricultural Development Division, during a one day visit to the Lower Shire I com­bined with limited access to a few reports. Two main aspects have been taken into consideration.

(a) The Lower Shire Report by Hunting Technical Services Limited (February,1981) has recommended two (100 ha each) areas for pilot irrigation development for which the water supply could be pro­vided by either surface or groundwater resources. Availability and development castings for the former have been providedj the equivalent information for groundwater has yet to be supplied and until this is done, the optimum proposals cannot be finalised.

(b) A general proposal for additional work in the Shire Valley has been submitted to the Dutch Government, principally concerned with the drilling of some 30 test wells and 80-100 observation wells over an 18 month period widely distributed over the whole valley. The programme envisages the recruitment of a master driller/instructor and a hydrochemist.

2. The existing knowledge of the groundwater resources of the Lower Shire appears insufficient for any practical evaluation of potential, feasibility and cost of development. The thickness of the main valley alluvium ranges from a few metres on the margins to more than 150 metres in the centre close to the Shire River. The adjacent and underlying bedrock formations include Basement Complex, Karoo system rocks (basalts, sands tones and shales) and younger Cretaceous sand­stones. Groundwater occurrence in the bedrock formations is largely unknown but (with the local exception of the basalts), it can be reasonably assumed that even if containing freshwater, the permeabilities will be insufficient to provide high yielding irrigation wells. The existing wells are mainly completed in the overlying alluvium. Water quality is variable and little precise knowledge appears to exist of the spatial distribution of water of varying quality or a correlation with identifiable controls such as discrete aquifer units, faulting or recharge occurrence.

2.1 Development to date has been on a small scale either in poorly-designed I drilled boreholes or hand dug wells, both generally fitted with hand­pumps. Groundwater flow appears to be directed towards the Shire River but the data are not generally precise enough to provide even two dimensional piezometric maps. Annual recharge rates are speculative and the few measurements which have been by the Borehole Maintenance Unit of seasonal water level changes in boreholes are unreliable. Predictions cannot, therefore, be made as yet of the consequences of large scale abstraction in terms of either drawdown or water quality.

2.2 To conclude! existing knowledge of groundwater occurrence in the Lower Shire Valley is generalised and limited. Some potential clearly exists but precise studies on virtually all basic aspects (detailed lithology and occurrence of aquifers, hydrochemistry, piezometry, permeability! storage and recharge) would now seem to be needed. The programme is basically conceptual and intended for discussion. If approved! more detailed proposals would need to be formulated.

3. RECOMMENDED PROGRAMME OF WORK

3.1 Stage 1. December 1981-March 1982.

3.2

An overriding priority is for the detailed reporting on all studies completed to date. The Report should include an inventory of all data with whatever analysis and interpretation is feasible. Particular consideration should be given to the potential of groundwater with respect to the two pilot areas (Alumenda and Tengani) which have been identified and recommended for development by irrigation techniques. Any additional work required to make this assessment is assigned to Stage 2 but planning recommendations should be included in the Stage 1 Report.

The present drilling programme should not be allowed to direct effort from the Final Reporting and consideration should be given to suspending operations if it seems likely to do so. In any event, it would seem worthwhile that any boreholes drilled should be completed, developed and thoroughly tested whilst the Gryphon Rig is on site. One recom­mendation that is made for further work at this stage is for the installation of the six available water level recorders on a selected group of observation wells. The measurements would then include changes during the coming wet season and would provide valuable in­formation on recharge conditions.

Stage 2. April 1982-June/September 1982.

The objectives for the second stage are as follows:

(a) Final feasibility investigation for assessing groundwater poten­tial for supply to the two pilot areas selected for development. Additional test drilling and aquifer testing may be required. Reporting will need to provide reliable predictions of quality and quantity of identified water resources! precise recommenda­tions of well design and costings for development.

(b) Investigations for the regional evaluation of groundwater re­sources( directed! in particular, to site selection for the subsequent test drilling programme. A main feature of this work is envisaged as down-hole survey of selected wells by suit­able borehole geophysical techniques (natural gamma, neutron/ formation density! fluid conductivity! flow logging and sampling). The distribution of water quality and an understanding of the hydrogeological controls. Account should also be taken of the type! locatio~s and scale of any projected demands, i.e. irrigation or ,domestic supplies. Consideration should also be given to the

3.3

relevance of additional geophysical surveys. Work previously carried out (Carruthers, 1981) has demonstrated the applicability of different techniques (seismic to differentiate consolidated bedrock formations from the overlying alluvium; magnetic measure­ments to identify the presence of basalt subcrop; resistivity to determine the occurrence of clay sediments/saline water at depth). However, because of the cost and specialist requirements of such requirements of such surveys, their particular relevance will need to be carefully assessed before embarking on a significant programme. More routine and simple geophysical studies could be carried out by the Project Hydrogeologist if equipment could be obtained. In this connection, resistivity and electromagnetic techniques should be considered and this equipment is available at Geological Survey (the equipment requires repair).

Stage 3. June/September 1982-March 1983.

In accordance with the results of the two preceding stages and in the context of realistic development options obtained by discussion with the Ministry of Agriculture and the Department of Lands, Valuation and Water, a programme of drilling and aquifer testing is envisaged. The drilling programme could include exploration, production and observation wells and conceivably could terminate before March 1983 if there was insufficient justification to continue. Investigations would also need to continue into other basic aspects l such as recharge. Results from the hydrometric network installed in Stages 1 and 2 would be assessed in combination with other hydrological analysis, e.g. runoff in marginal uplands, base flow, etc. Local infiltration measurements might also be included, using geochemical or water content/ potential measurements in the unsaturated zone.

4. STAFF

Essential professional staff include the hydrogeologist, master driller/instructor and llhydrochemist 11

• The latter should preferably be technically oriented and able to assist in a wide range of measure­ment techniques including sampling, borehole logging, aquifer testing, etc. Chemical analysis could be carried out in the Department of Lands, Valuation and Water laboratory in Lilongwe. Consultant inputs are recommended in geochemistry (one man month), geophysics (three man months, provisional) and overall hydrogeological review (one man month) .

5. COSTING

Precise details can be prepared once the programme has been approved in principle. Main costs will be for staff (both expatriate and local counterpart), transport and drilling. On the assumption that depreciation on the rig is not taken into account of, some K2S0,OOO could be a reasonable estimate for operating and materials costs of the drilling programme.

FILE REF NO Lvw/81/l

RURAL GROUNDWATER SUPPLY AN ALTERNATIVE STRATEGY

BACKGROUND

Between 1968 and 1980, 729 Rural Water Supply boreholes have been provided under the District Development Committee Programme of Rural Development (Ope) and funded by various external donors through the Christian Service Committee of the Churches of Malawi. The effectiveness of this on-going programme is in question and the major criticisms have been:-

(a) escalating cost of boreholes,

(b) lack of technical planning in the selection of sites to be forwarded to SCS for funding,

(c) high maintenance cost of boreholes,

(d) inefficient use of limited skilled manpower and machinery by drilling widely dispersed boreholes, with the inevitable lack of close supervision,

(e) the long lead-time required to plan a particular year's programme, e.g. it takes eight or nine months for the programme to be approved by which time only a small proportion of the dry season remains for construction work.

During the period 1971 to 1980, the average cost of boreholes drilled by the Government rigs has increased from Kl,232 to K3,766 (not including the cost of handpumps) with deeper boreholes costing often in exceSS of k7,000. A major part of this increase arises from fuel costs and running costs of vehicles. Should the Borehole Fund of DLVW be committed to a dispersed programme, it is clear that running costs will continue to increase while productivity in terms of number of boreholes drilled per year may well decline unless funds are set aside to capitalise the replacement of elderly vehicles and drilling rigs.

A NEW APPROACH

The Department has become fully aware of the short-comings of its inherited borehole programme and considerable effort has been devoted during the last 18 months to the solution of problems associated with supply of groundwater to rural communities (it is estimated that for 75% of the rural population there is no alternative source of safe domestic water other than ground­water) .

A major step forward has been the development of a new type of low-cost but highly efficient borehole and the evolution of an integrated project approach "to rural groundwater supplies. The main stages in its evolution can be summarised as follows;-

(a) detailed hydrogeologicl evaluation which deomonstrated the occurrence of an extensive, shallow, weathered rock aquifer throughout much of the 'basement' or 'plateau' areas of Malawi (e.g. Shire Highlands, Lilongwe

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Plain, South Rukuru etc). Until recently the existence of this aquifer has been ignored and boreholes have been drilled deep into fresh rock in the search for water. A consequence of the recognition of the importance of this aquifer is that high yielding boreholes can be drilled to shallow depths (c. 20 m instead of c. 50 m in the past) in the soft, overlying, weathered material. This permits the use of very lightweight and inexpensive drilling rigs which can be towed by a small vehicle or even by hand if necessary. A further consequence is the greatly reduced need for site surveying. Adequate yields can be obtained in many areas of Malawi wherever the weathered profile is adequately developed.

(b) A search for locally-available materials to replace imported items and, at the same time, careful hydraulic design of important components of the borehole such as screen and gravel pack. Imported mild-steel casing has been replaced by locally extruded and locally slotted PVC casing with a hundredfold increase in open area (i.e. where water passes from the aquifer into the borehole) resulting in greatly improved yields and increased life due to the inert nature of PVC. A national survey for correctly-graded, gravel-pack material (which prevents movement of sand into a borehole - one of the major causes of excessive pump wear) has revealed that the lakeshore beach sand at several sites has the characteristics of a perfect gravel filter.

(c) A study of the components of the cost of the dispersed borehole programme shows clearly that a very large proportion of the total annual expenditure is on vehicle spares, repairs, replacement and fuel. At present each drilling rig is serviced by a 7-ton truck which is absolutely essential if the rig is to function as an independent unit. If drilling rigs were kept close together, four rigs could be serviced by one vehicle. Furthermore, if the drilling programme is changed so that boreholes are constructed in one area a time, distances between boreholes are reduced allowing a tractor and trailer to be used. This would also solve the problem of off­road access which plagues the present construction programme.

The proposal for IIIntegrated Projects for Rural Groundwater Supplies!' follows naturally. ThiS, in essence, involves the complete provision of groundwater points in one area at a time by a project team which would:

(i) protect existing shallow wells,

(ii) rehabilitate existing boreholes

(iii) construct protected dug-wells

(iv) drill new low-cost boreholes

(v) establish a comprehensive maintenance system.

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THE UPPER LIVULEZI TECHNICAL FEASIBILITY PROJECT

The new borehole designs tested in 1980, with assistance from the UNDP in a project, 'Design of low-cost boreholes for rural water supplies'. Shallow boreholes, equipped with locally manufactured PVC casing, were drilled at Chitedze and two have since been equipped with electric submersible pumps to supply the Agricultural Research Station.

This was followed by a full-scale technical feasibility study of the integrated approach to groundwater development. 24 low-cost boreholes and 10 dug wells were constructed in the Upper Livulezi Valley, in Ntcheu District. The project was supervised by one hydrogeologist and was in every way a success in proving the technical and economic feasibility of the new approach. Seven thousand people were supplied by waterpoints at a cost of less than K40,OOO, i.e. per capita cost of K5 - K6, which is considerably less than any other rural water supply option (e.g. K1S - K20 per capita for current rural piped water schemes).

In summary I cost savings were made in the following ways:-

(a) the use of lightweight and inexpensive rigs! drilling to one-third of earlier depths in one-third of the time

(b) minimal expensive on survey (sites largely chosen by each village)

(c) the use of locally-manufactured 4" PVC casing in place of 6" steel casing imported from UK

(d) a 75 per cent reduction in vehicle running costs by servicing several rigs with one vehicle and minimising distances to be travelled between sites

(e) greater supervision resulting in increased efficiency of operation and a high borehole success rate

(f) greater community involvement, e.g. village site selection, provision of drilling labourers and watchmen, supply of water stones, and bricks and construction (supervised) of borehole surround.

It was demonstrated that the cost of boreholes can be brought down to about KIOOO - K1200 (without handpumps) which is less than one-third of the 1980 cost of boreholes.

HANDPUMPS AND HANDPUMP MAINTENANCE

Two interdependent elements remain to be proved by extensive field trials. These are the new handpumps, designed by the Department and manufactured locally, and a maintenance system to replace the inefficient and costly service now operating. To a large extent the new maintenance system depends on the successful development of the new type of handpump. At present, the heavy imported handpumps, although robust in the field, need to be lifted by winch (truck-mounted) in order to effect even the most basic of repairs, such as the replacement of cup leathers. Thus, a specialist team in an expensive vehicle is called in from a District Maintenance centre to effect a repair in which the parts to be replaced cost only a few kwacha.

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The most important feature of the new pump is the facility to remove by hand the connecting rods, piston, foot valve and rising main through the pump head, which remains in place over the borehole. This eliminates the need for a winch, and opens up for the first time the possibility of village-level care-taking and area maintenance with Government support only required to ensure the adequate supply and distribution of spare parts.

The successful establishment of such a maintenance structure would reduce maintenance costs to a fraction of their former level, and would encourage village participation in the upkeep of their water supply. This sense of ownership and participation has been shown to be important in the piped water projects and in other countries which face the same problems.

The Department of Lands, Valuation and Water intends to carry out field trials of the new handpump and to develop a community-based maintenance system in a pilot programme in the Upper Livulezi Valley. This will extend the work of the feasibility project to cover the whole of the Upper Livulezi and provide water supplies for an estimated 1990 population of 60,000 people. The field trials of handpumps will form part of the UN/World Bank Global Handpump Project 1 in which Malawi is likely to become a 'lead' country as a result of the developments outlined above.

FUTURE STRATEGY

The proven feasibility of this type of integrated rural groundwater programme has already attracted interest from the World Bank and other donors. Its features of increased production at a significantly lower cost, together with the potential for establishing a community-based maintenance system are attractive to donors r and such integrated schemes could be a major breakthrough in supplying water to the rural population during the International Drinking Water Supply and Sanitation Decade. At the present time, funds are being made available for an integrated project for rural groundwater supply as part of the Dowa West Development Project; the World Bank is pressing for a similar approach to be applied in the Karonga-Chitipa Rural Development Project and proposals have been made for the Salima Lakeshore Agricultural Development Project to include such an approach in their next five year plan.

In terms of the Decade target of providing water for all by the year 1990, the integrated approach is considered to offer the only realistic solution to achieving the stated goal. The Department of Lands, Valuation and Water would, therefore, seek approval to concentrate its resources on developing and expanding such integrated projects in the three regions, if necessary at the expense of the grossly inefficient DDC programme. The present appraisal of the DDC programme by the CSC, provides an opportunity for Government to re-assess the achievements of the borehole construction programme to date in relation to the increased production and cost savings afforded by the new approach outlined above. It is clear that certain areas will have to wait longer for boreholes to be provided butr if the new system is adopted, these areas will not only have eventually completely adequate water supplies but also will have a maintenance system to safeguard those supplies at a minimal cost to Government and the local community. Should it be ruled that the new approach cannot be given immediate priority, it is the considered

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opinion of the professional officers in DLVW that Malawi has very little chance of achieving any significant part of the goals of the International DRinking Water Supply and Sanitation Decade. At least 75 per cent of the rural population will have to depend on groundwater for drinking water. With upwards of 10,000 new boreholes required to serve the existing rural population, it would take a hundred years to cover the country with a dispersed programme.

It is opportune, therefore, to consider very carefully the implications of continuing with the dispersed programme when there is now a viable cheaper and more productive alternative which donors themselves are ready to adopt. It is recognised, however r that in order to replace the DDC programme! the Department of Lands! Valuation and Water must show how it proposes to cover the whole country and within what timescale.

The overall strategy can only be presented in outline at this stage because of the rapid evolvement of new ideas and the iterative process of testing the new ideas in the field and feeding-back information from the field trials to make further cost savings.

Within the foreseeable future (up to 1985/86) the Department of Lands, Valuation and water aims to phase its programme of groundwater development with that of the National Rural Development Programme. Where certain priority areas exist, such as for example the Lower Shire where a borehole rehabilitation programme is required as soon as possible, departures from the NRDP programme will be expected.

After 1985/86, the same principle of integrating with NRDP will apply but, by that time, an appraisal of the relative speeds of the two programmes will be possible and further departure may be expected unless the benefits of phasing-in with NRDP are overriding. It should be mentioned that the phasing proposal for groundwater is in line with the way the Rural Piped water Programme integrates with the NRDP.

CONCLUSION

The Department of Lands, Valuation and Water is proposing a new approach to the development of groundwater resources. In principle it differs little from the approach adopted by the Rural Piped Water Supply Programme but the existence of a prior commitment to the DDC borehole programme is producing competition for funding and possible political implications should the DDC programme be cut.

At the same time, it is no longer possible to carry out both the full DDC programme of 100 boreholes per year in addition to the other more cost­effective programmes due to start next year.

It would appear necessary to phase out the DDC programme! possibly by spreading the 1981/82 programme over two financial years (in any case it is now seriously retarded by the delay in confirming the programme). This would imply explaining to the DDC's that there would be no request for new

-6-

sites this December and thereafter, the new integrated approach outlined in this paper would provide a more efficient and less costly method of achieving the targets of the International Drinking water Supply and Sanitation Decade.

The Department wishes to request the CSC to divert a part of the funds available for rural water supply to a reduced DDC programme and part to the Upper Livulezi Integrated Project for Rural Groundwater Supplies. The latter project is a key link in the evaluation of a system of rural water supplies from groundwater that Malawi can afford.

NOVEMBER, 1981

B

Ref. No 2.3.5 OCTOBER 1981

DEVELOPMENT PROJECT

PROJECT TITLE UPPER LIVULEZI INTEGRATED PROJECT FOR RURAL GROUNDWATER SUPPLIES

RESPONSIBLE MINISTRY OFFICE OF THE PRESIDENT AND CABINET/DEPARTMENT OF LANDS, VALUATION & WATER

1. OBJECTIVES OF THE PROJECT:

To implement on a major project scale an integrated system of providing dug-well protection and borehole rehabilitation together with the construction of new low-cost boreholes and dug-wells in the Upper Livulezi Valley in Ntcheu District.

To optimise the utilisation of groundwater resources.

To provide minimum-cost development of groundwater for rural domestic supplies.

To develop the self-help concept within the borehole drilling programme.

To involve the community in handpump maintenance.

To participate in the UNDP/World Bank Global Handpump Project.

2. GOALS OF THE PROJECT:

To supply clean potable water to 60,000 people in accordance with the goals of the International Drinking Water Supply and Sanitation Decade.

3. PROJECT LIFE:

18 months Construction Phase with a 3-year Maintenance Evaluation Phase.

4. TOTAL PROJECT COST:

K 470,000 for water supplies.

5. FINANCIAL SUMMARY:

(a) Funds required by financial year:-

1981/82 1982/83 1983/84 1984/85 1985/86 Total

87,000 323,000 20,000 20,000 20,000 470,000

- 2 -

(b) Previous expenditure:

Up to February, 1981, there were 13 boreholes and 6 protected wells with hand pumps in the Upper Livulezi Valley. Since March, 1981, the Groundwater Project of the Department of Lands, Valuation and water has carried out a technical feasibility investigation for an integrated approach to rural water supply using groundwater sourceSi 24 low-cost boreholes and dug wells have been constructed and equipped at a net cost of K36,000.

(c) Proposed source of finance:

Christian Service Committee of the Churches of Malawi, British Government, UNICEF and other external funding for pumps and materials, technical contribution from UK aided Groundwater Project and direction and monitoring of the field testing of hand-pumps by the UNDP/World Bank Global Pumps Project. Malawi Government will fund maintenance costs.

6. PROJECT TARGETS:

(i) Provision of water points in the Upper Livulezi Valley supplying a minimum of 27 litres per head of clean (but untreated) water to 60,000 people at a basic cost of K6 per capita. This is an area which cannot be served by piped water because of the lack of suitable rivers with projected catchments.

(ii) Water points will be constructed within 500 metres one-way walking distance of the great majority of the population to be served (except in areas of very scattered settlement where walking distances could be greater). Dug wells will serve a maximum of 125 people and boreholes 250 people.

(iii) A project of 4~1 years duration during which a system for integrating five components of the rural groundwater development programme will be extended to cover the whole of the Upper Livulezi Valley. The main work will be carried out in the first 18 month period followed by a 3 year period for establishing a minimum cost maintenance system. The five components are;-

(a) the protection of existing shallow wells,

(b) the rehabilitation of existing boreholes,

(c) the construction of new dug wells,

(d) the construction of new low-cost boreholes t

(e) the establishment of a system for maintaining water points. This will be largely community-based and will include training of community nominees.

(iv) The project will incorporate the field testing of rural water supply hand-pumps under the UNDP/World Bank Global Handpump Project. This component includes the development of locally manufactured handpumps.

- 3 -

(v) Unquantifiable targets will be:

(a) Optimum use of a limited natural resource.

(b) Low-cost development of rural groundwater supplies.

(c) Introduction of self-help participation in borehole construction.

(d) Improvement in general health and living standards of the poorest sector of the community.

7. BACKGROUND INFORMATION:

The formation of the Department of Lands, Valuation & Water has enabled a more integrated approach to the problems of rural water supply than has been possible hitherto. In the newly-formed Ground­water Section of the Water Resources Branch of the Department, the three functional units of Groundwater Resources, Borehole Programme and Dug Wells have been combined administratively for the first time.

Aiming towards the goals of the International Drinking Water Supply and Sanitation Decade, the Department is integrating the programme of all water supply functional units in a rational manner, in order to plan the most appropriate and most economical type of supply for each and every area. This will count upon maximising self-help partici­pation. The overall national target will encompass all rural areas and a strategy is being evolved to do this. In the National Water Resources Master Plan, areas within each district where piped water supply is possible will be defined and the remainder planned for networks of water paints drawing on groundwater.

The Upper Livulezi Valley has recently been withdrawn from the piped water programme owing to increasing cultivation in the catchment of the surface water sources. The Upper Livulezi groundwater project is to replace it and at the same time will be the first full-scale testing of the new integrated approach. The concentration of plant, vehicles and technical expertise and the closer liaison with the D.C.C. made possible by such a scheme, will allow a much more cost-effective use of resources than has been the case with the previous dispersed borehole programme. It will cut significantly the ttper capita" cost of providing groundwater pOints for rural communities. A low-cost borehole provided under such a programme would comprise a relatively shallow, PVC-lined, correctly gravel-packed and hydraulically efficient borehole and would cost in the region of Kl,5900 (Appendix B) compared with an average cost at present of K4,500 for a steel-cased, deeper and less efficient borehole. Dug wells are estimated to cost K750 (Appendix B). Both costs include the handpump and water point surround.

The projected 1990 population of the area is 60,000 of whom 7,000 have been served by the feasibility investigation and 4,000 existing boreholes and wells.

- 4 -

8. SUCCESS SO FAR ACHIEVED:

The Groundwater Section of the Department, supervised by Groundwater Project staff has recently completed a small scale feasibility investi­gation in the Livulezi area in which 24 new low-cost boreholes and 10 dug-wells were installed at spacings to limit walking distance to 500 metres (maximum), 7500 people have been provided with a minimum quantity of 27 litres per day of clean water. The total cost of this work was K36,OOO not including the cost of pumps provided from Commodity Aid Stocks.

9. EXECUTION AND SUPERVISION:

The project will be executed and supervised by the Groundwater Section of the Department of Lands, Valuation and Water. The UK/ODA Groundwater Team within the Department will provide overall direction of the pilot project.

10. HANDPUMPS:

The Upper Livulezi Project is to be used for Malawi's handpump evaluation programme as part of the UNDPjWorld Bank Global Handpump Project. The prime objective of this latter project is the manufactured, easily installed and largely maintained by the user community.

The Malawi Government has agreed to participate in the UNDPjWorld Bank Global Handpump Project. Handpumps for testing and evaluation will be supplied by external donors supporting the Upper Livulezi Project. The Government input will be:-

(a) Project Hydrogeologist who will coordinate Government's involve­ment.

(b) Field Accommodation for a UN Volunteer at the Project Head­quarters in the Livulezi Area.

(c) Logistic support to the UNV at the discretion of the project Hydrogeologist which will include office, stores, workshop, transport, secretarial facilities etc. and essential running costs for any vehicle supplied to the UNV.

The UNDPjWorld Bank input will be:-

(a) assistance of the UNDPjWB Regional Project Officer (RPO) in the following activities:

(i) development, monitoring and evaluation of the project,

(ii) feed-back of information from other African projects,

(iii) provision of modifications and designs for local-produced handpumps and accessories I

(iv) supply of selected materials for prototypes,

(v) selection and procurement of pumps,

(vi) identification of and liaison with other donors,

(vii) overall direction of the UN volunteer,

- 5 -

(b) recruitment and financial support of the UN Volunteer. The duties of the UNV will be:-

(i) to supervise correct installation of handpump,

(ii) to develop the system of handpump performance monitoring and evaluation,

(iii) to report failures to the maintenance team for immediate attention and to assist accordingly,

(iv) assist in the development and quality control of locally­produced components,

(v) to report through the Department of Lands, Valuation and Water to RPO, Nairobi.

11. EQUIPMENT AND MATERIALS:

Up to four percussion drilling rigs would be provided by the Department of Lands, Valuation and Water to carry out borehole construction under the direct supervision of the project hydrogeologist.

The following vehicles would also be provided by the Department:-

(a) one tractor and trailer to service rigs and well-digging teams,

(b) one light pick-up for the project hydrogeologist,

(c) three motorcycles.

Major material requirements for the construction of new boreholes would be PVC screen and accessories purchased locally. Correctly­graded Lakeshore beach sand would be used as a gravel pack and cement would be required for plinth, surround and washing slab. For the dug wells, the major requirement is cement for casting rings and slabs and for the surface works (plinth, surround and washing slab).

12. MAINTENANCE:

Maintenance of the hamdpumps and water supply will be effected by an improved multi-tiered system which will involve the maximum of community participation at the village level. It will comprise:-

(i) Central GoveE!1ment/Departmental Level

(a) Planning and strategy (handpump policy) . (b) Research and development in hamdpump design, with the

major target to minimise and simplify maintenance. (c) Training of district pump technicians. (d) Procurement of pumps, spares, tools and equipment. (e) Monitoring of the maintenance programme. (f) Distribution of equipment to district stores.

(ii) DIstrict of Regional Level

(a) Supervision of about 1000 pumps by a trained technician (District Pump Technician) with support driver and one vehicle (1 ton pick-up) .

(b) Store for spares.

- 6 -

(c) Maintenance records for all water points within district. (d) Training of area pump mechanics. (e) Liaison with District Development Committee. (f) Periodic inspection of area water points. (g) Repair or replacement beyond capabilities of area

mechanics. (h) Estimate of annual maintenance requirements for spares

etc.

(iii) Area Level

(a) Area Pump Mechanics chosen on the basis of skills shown during construction phase. Further training by District Pump Technician or DLVW training courses. Supervision of about 50 pumps.

(b) Visits to each pump/village at least once every four months (bicycle) .

(c) Recording all repair work and reporting to District Pump Technician.

(iv) Village .Level

(a) Village Pump Attendants chosen by the village Development Committee responsible for all pumps in one village (could be men or women) .

(b) Attendants ensure that the pumps are properly used, pump surrounds are kept clean and acts of vandalism are prevented.

(c) Minor replacement, preventive maintenance and all simple repairs will be effected at this level. When major repairs or replacement parts are required the attendants will notify the Area Pump Mechanic.

(d) The Attendants will be trained on site by project assistants at the time of installation.

PROJECT TITLE

RESPONSIBLE MINISTRY

- 7 -

APPENDIX A OCTOBER 1981

UPPER LIVULEZI INTEGRATED PROJECT FOR RURAL GROUND·· WATER SUPPLIES

OFFICE OF THE PRESIDENT AND CABINET: DEPARTMENT OF LANDS, VALUATION AND WATER

1. PROJECT OFFICER: CHIEF WATER RESOURCES OFFICER

2. FINANCIAL DETAILS

(a) Details of expenditure Total Project Cost K470,000

CONSTRUCTION >!iUNTENA.NCE EVALUATION PHASE

PHASE

. __ ._----_._-_ .. __ ..•. _---------

1981/82 1982/83 1983/84 1984/85 1985/86

003 Water Supplies (a) Borehole and

dug wells 60,000 275,000

(b) Rehabilitation 6,000 6,000

(c) Establishment of 18,000 18,000 18,000 a maintenance system

010 Special expendi- 10,000 , ture (stores for materials)

Contingencies 11,000 42,000 2,000 2,000 2,000 and inflation

87,000 323,000 20,000 20,000 20,000 I

- 8 -

Appendix A (continued)

Notes on Expenditure

(i)+ Each completed water pOint, either borehole or dug well, will be involved together with a completion on the basis of itemised costs (Appendix E) of the following'-

(a) drilling or digging,

(b) testing and completion operations,

(c) construction materials,

(d) handpump,

- 9 -

APPENDIX B

BREAKDOWN OF COSTS PER WATER POINT

1) Typical low-:cost borehole

Percussion drilled to 20 m at 200 mm diameter, equipped with 8 m of blank 110 mm PVC casing and 12 m of slotted 110 mm PVC screen (12% open area, 0.75 mm slot).

Annulus filled with 0.7-2.5 mm graded (beach sand) filter, handpump installed and protection apron constructed (including drain and washing slab). All locally available building materials supplied by the communi ty .

Sample costs

(a) Drilling

(b) Other operations:

Development 4 hours Testing 4 hours Movement of rig (say 5 km) Rigging up and down Cement grout

(c) Materials:

PVC casing plain 8 m PVC casing slotted 12 m PVC end cap and centrallisers Beach sand Cement for apron

(d) Handpump:

0-15 m 15-20 m

Malawi Kwacha (1 US$ = 0.9MK)

450 200

Sub total 650

80 80 35 50 20

Sub total 265

50 140

10 60 50

Sub total 310

(a) (b)

(c)

locally manufactured 'Malawi pump' @ MK250 Total MK 1500 MK 2000 MK 2000

Consallen pump @ MK750 Total India MK 11 @ MK750 Total

- 10 -

Appendix B (continued

2. Typical dug well

6 m deep, 2 off/l m diameter x 1 m deep concrete rings inserted with a slab cover, clay back-filled, top slab, handpump and apron with washing slab.

Sample costs

Digging (to include wells team supervision, transport and all other site activities)

Locally made pump 2 concrete slabs 2 concrete rings Cement for apron

total dug well cost

450 150

50 50 50

MK 750

- 11 -

APPENDIX C

DETAILED PROJECT COSTS:

388 water pOint units: each unit serving 125 people. Each borehole supplies 250 people and comprises tw~~a~er pOint units and each shallow well serves 125 people and comprises one water point unit. Possible water point totals: 144 boreholes and 100 shallow wells (final decision rests with project hydrogeologist on site).

COST BREAKDOWN:

A. Construction

20 boreholes fitted with Consallen pumps 70 boreholes fitted with India Mark 11 pumps 54 boreholes fitted with 'Malawi' pumps 100 shallow wells

Total

B. Rehabilitation

37 boreholes (Malawi pumps) fitted Malawi pumps and buklding or rebuilding aprons

cement for 13 aprons

Total

C. Stores

To be constructed in Project Area Total

D. Maintenance

Costed at approximately 5% per year at capital costs for three years to establish a maintenance system, designed as described under part 12 above to maximise community participation. Cost per year K18,000 Total

E. Contingencies and Infiltration

At approximately 15% of total Projects cost (see Appendix A for Total annual costs) . Total

MK

40,000 140,000 81,000 75,000

335,000

9,250 2,100

650

12,000 -----

10,000

59,000

- 12 -

Appendix C (continued)

F. Project .Total

MK470,000

COSTS DISTRIBUTED BY DONOR:

A. British Government

20 Consallen handpumps to be supplied by UK Overseas Development Administration

(Plus input by 2 Technical Cooperation Officers of the ODA Groundwater Project not costed to the Livulezi Project)

B. UNICEF

25 India MK 11 handpumps CIF Malawi PVC borehole casing, screen and rising

main for 50 boreholes 25 Malawi MK I preproduction handpumps 300 bags cement

Total Approx.

Total

MK

15,000

10,000

ll,923 66,250

2,130

30,303

C. Material costs to be funded by other external donors

45 India MK II handpumps @ MK750 33,750 66 Malawi MK I handpumps @ MK250 16,500 100 Dug-well handpumps

(locally produced) @ MK150 15,000 PVC borehole casing, screen

and cups for 94 boreholes 18,800 Cement for 94 boreholes and

100 dug wells 20,000 Contingencies __ 1_,827

Total 105,947

13 -

Appendix C (continued)

D. Drilling and Construction Costs (proposed funding by Christian Service Committee of the Churches of 1'1alawi

144 boreholes @ MK1250 + 15% contingency Total 207,000

E. Construction Costs of Shallow-wells to be funded by other external donor

100 shallow wells @ ~'K450 + 15', contingency Total

F. Maintenance Costs to be borne by Malawi Government

3 years @ MK20,000 per annum Total

G. Drilling and other Equipment

To be provided by the Groundwater Section of DLVW. Acknowledgement is made of the funds for equipment to be used in the Project from UNDTCD "Design of low-cost boreholes for rural water supplies project" MLW/80/003.

H. UNDP/WB Global Handpump Project

UNDP/World Bank will be providing the UN Volunteer and support costs together with periodic assistance from the Regional Project Officer in Nairobi.

60,000

Appendix II.

RANNEY (COLLECTOR) WELLS.

1. Typical Design.

A Ranney well consists of a central caisson and radial laterals dist­ributed around the caisson and occurring in one or more tiers. The central caisson is constructed of poured-in-place reinforced concrete and consists of a vertical shaft some 4 m in diameter with wall thick­ness of 45-61 cm. The laterals are commonly about 22 cm diameter with lengths between 30 and 75 m and lined with slotted steel screen. Screen slot size is approximately 1 cm and 20% open area is usual. The surrounding aquifer is developed naturally.

2. Use.

Ranney wells are high capacity wells constructed in thin, near surface, laterally extensive and high permeability aquifers with a free water table. A typical location is in river gravels with induced recharge occurring. Costs of construction are high.

The use of a Ranney well in the laterally extensive but low permeability weathered basement aquifer in Malawi would seem inappropriate on first consideration. The justification may exist if sustained and moderately high abstractions by motorised pumps prove feasible and if costs can be kept to levels which are economically acceptable in relation to the volumes of water produced.

3. Preliminary Analysis.

Assumptions: homogeneous, laterally extensive aquifer, 30 ID thick with a low permeability of 1 m/day (a conservative value). Table I shows the radii of influence for design yields of 10 and 20 m3/h and 12 hour pumping days for various assumed rates of steady recharge.

TABLE I

Radius of Influence in metres for constant vertical recharge and discharging central well (Q) in m3/h.

Recharge in m/a 0.1 ._ .........•..•.•........ --_. __ .•.•.. - ----_ .....

Q m3/h 10

20

380

540

0.2

270

380

0.4

190 metres

270

Preliminary analysis for steady state drawdowns assuming constant re­charge rates can be calculated for a single well of 0.05 m radius and for a Ranney well with 4 radial collectors, each 30 m in length. The effective 'radius ' of the Ranney well according to general statistical data for a single tier of 4 radial collectors is 75% of the length of

-

one lateral, i.e. 22.5 m. In the Table 11 below, the reduction in transmissivity in consequence of drawdown has not been allowed for. It will clearly be considerable where the 'theoretical drawdowns' are high and the true drawdowns could exceed the calculated values by 50-100%.

TABLE 11

computed steady-state drawdowns (in metres) assuming constant recharge and no reduction in aquifer thickness in consequence of drawdown.

Recharge in m/a 0.1 0.2 0.4 ._-- .. ---,,--~

q (m 3/hour) 10 20 10 20 10

Single well of

20

0.05 m radius 6.1 15.4 5.S 14.5 5.6 13.7

Ranney Well with 4 laterals 1.6 3.7 1.3 3.2 1.1

The higher rates of recharge used are probable if the heavy days which are the end products of the tropical weathering cycle have been removed by later erosion. The lower rates are perhaps more likely on the uniform savanna plain regions of Malawi. The results do demonstrate the virtual incapacity of single narrow-diameter wells to sustain yields of 10-20 m3/h. The relatively small drawdowns of the Ranney well do indicate that sustained abstractions are possible under the range of recharge rates and other assumptions used.

Actual recharge will be markedly seasonal and unsteady state conditions have to be allowed for with significant periods of nil to negligible recharge. The solution obtained by Hantush and Papadopulos for pumping levels in a Ranney well is shown below and has been applied to the assumed conditions of the weathered basement aquifer including a specific yield of 0.05. All other assumptions required by the solution are satisfied (but not listed here) .

Xl· plane

Collector -----,

- 2fc

,11<-_--­Zi

Land sur foce

Water table

Cone of

Cl)_ t _ ... __ ) m

~7~q;;~~;,~e:~~~7J/?, No leo~oge

Water Table Aquifer with Collector Well.

2.7

s = W L +_L_ I'W _--,.,-Q (( I' ) N - I [ ( 1" )

,"' 4rrPmNL 4Pml/S, 1£ 4Pml/S,

-, W( 'e' )J + 2NI + !!!.. In ( (m/rrrL)' J '4Pml/S, '21/- 2[1 - cos rr(2Zi + 'L)J/m

+ 4m(NL - I) ~ ~[:: _ w(_nrr_r, ,o)J [cos '_lrr_Z_i cos _nrr_(,-Z-'-i"":+_'-'I,,-.lJJ 7T1J., n=ln2 m m 111

in which M' is an integer large enough so that M' > m/2". The functions W(u) and W(u,O) are defined:

P

NL

t

Sy

W (u)

m

l'

u' u3 u' IV(u) = -0.5772 - In u + u - -, + -, - -, + ...

2.2. 3.3. 4.4.

IV(u,O) = f K,(rHr

Permeability (1 m/day)

Number of laterals

Time (10 and 100 days)

Specific Yield (0.05)

and W (u,O) Well functions

Vertical position of laterals (20 m below water table)

30 m

1 +r L c

Drawdown in collector caisson (metres)

Radius of lateral (30 m)

After 10 days the calculated pumping level will be 2.0 m and after 100 days, it will be 2.75 m. Both these values are comparatively low and would result in moderate reductions in effective transmissivity and hence increased drawdowns. However actual conditions could be more favourable than those used in the analysis since higher perme­abilities than 1 mid have been obtained at some sites and additionally, the upper more clayey levels in which drawdowns will be effective have relatively lower permeability than the deeper, less chemically weathered intervals.

In the Report to follow, analyis of Ranney well operations in an actual site condition in Malawi will be analysed and constructional techniques and possible costs will be discussed, with a view to commencing an experimental study.