BRITISH GEOLOGICAL SURVEY Natural Environment Research Council

TECHNICAL REPORT

Hydrogeology Series

Report WD/89/22R

Back to Office Report on a Visit to Zimbabwe, 26th May to lOth June 1989

P J Chilton

A report prepared for the Overseas Development Administration

Keyworth, Nottinghamshire British Geological Survey 1989

Crown copyright 1989

SUMMARY

The first collector well on the Lowveld Research Station at Chiredzi has been successfully completed to a depth of 12 m and test pumped at 1 l/sec. A permanent pump has been installed and the well is now ready to provide irrigation water. A programme of hydrogeological observations at and around the well has been initiated. Preliminary visits were made to areas where on -farm collector wells mi ght be sited. Exploratory dri 11 i ng to confi rm a site for a collector well in all uv i um was due to commence immediately after the visit. The TC proposal for developing small-scale irrigation from collector wells in communal lands rests with the Development Division in Lilongwe for final revision before being submitted through the normal Zimbabwe Government channels to the British High Commission and it is not possible at this stage to predict a start date.

1. INTRODUCTION

Chiredzi in the Lowveld of Zimbabwe is the site for the field activities in the project "Development of small-scale irrigation systems using 1 imited, shallow groundwater resources". Being a joint project implemented by BGS and IH, regular short visits are made by staff of both institutes, and it is usually more effective to combine visits where possible and where the programme dictates. The last joint visit was in October 1988 (BGS report WD/88/19R) and Dr R Herbert visited in April 1989 (BGS report WD/89/6R). As both IH and BGS staff produce visit reports, the present report concentrates on hydrogeological aspects of the visit, except where a broader standpoint is essential to continuity and understanding of the sequence of events during the visit. The large amount of hydrogeological data obtained at Chiredzi is not included in this visit report; a separate technical report containing all the construction and testing results, analysis and discussion will be prepared.

2. OBJECTIVES OF PRESENT VISIT

The main hydrogeological objectives of the present visit were:

(a) to collect and review all construction, testing and cost data for the well at Chi redzi,

(b) to begin the process of selection of possible sites for collector wells in basement areas away from the LRS, Chiredzi, i.e. in communal lands or resettlement areas,

(c) to define a progamme of hydrogeological data collection to enable the long-term sustainabil ity of collector well performance to be evaluated.

Additional objectives were to review the suitability of sites for testing the construction of collector wells in alluvial strata, and to discuss with all appropriate organisations the progress of the current programme and the present situation of the associated TC proposal for the development of small-scale irrigation. These organisations include

principally the Department of Research and Special ist Services (DRSS) of the Ministry of Agriculture, the Ministry of Energy and Water Resources Development (MEWRD), the British High Commission (BHC), and any representatives of the British Development Division in Southern Africa (BDDSA) who were in Harare at the time.

3. ITINERARY

26/27 May

27 May

28 May

29 May

30 May

31 May

1 June

2 June

3 June

4 June

5 June

JC and CB travel London-Harare.

Saturday. Visit friends in Harare.

Sunday. Working on a report not connected with this visit.

Meetings with Mr D Tolson (BHC), Mr A Tainsh (BDDSA Agricultural Adviser), Mr R Fenner (DRSS), Messrs I Anderson and P Brin (TCO soil chemistry section, DRSS), and P Sinnett Jones (MEWRD). Purchase of maps and reports from Geological Survey.

JC and CB travel by road brief meeting with Mr I Research Station, Chiredzi. irrigation trials site.

to Chiredzi via Gutu. Initial, Mharapara, head of the Lowveld

Visit to the collector well and

Meeting with Mr Mharapara (all) to discuss objectives and programme for present visit. Visit (with P Rastall) to MEWRD rig drilling exploratory boreholes in alluvium at Hippo Valley Estates. Visit to Richard Owen's wells and gardens at Makusia School on the south side of the Lundi River, to review the suitability of the area for collector well sites. Discussions with P Rastall of collector well test pumping results.

Visit (JC and PR) to Nyahombe Resettlement Scheme, 70 km west of Chiredzi on Ngundu road, to make preliminary assessment of potential for collector wells. Met resettlement officer. Also visited new resettlement area to the NE of Nyahombe for same purpose. Discussion of further collector well on the LRS site.

Visit to MEWRD rig at Hippo Valley Estates. Preparation for test pumping, including installation of autographic water level recorders. Discussion of well costs and preparation of cost summary.

Carry out additional test pumping of collector well, with detailed drawdown and recovery observations in exploratory boreholes.

Report writing. Check recorders at test site.

Preparation and discussion of programme of data collection. Report writing. Further discussion of collector well costs. Check recorders at site.

6 June Visit to Nyahombe Resettlement Scheme (Batchelor, Mharapara, Rastall and Murata) accompanied by representative.

Chilton, Agritex

7 June Visit to MEWRD rig at Hippo Valley Estates. Collection of water samples. Removal of recorders from observation boreholes and reinstall recorder on collector well. Discussion of programme of data collection and future drilling programme.

8 June

9 June

10 June

Discussions at LRS, Chiredzi. Drive to Harare via Masvingo.

Meetings (CB & JC) with Mrs J Laurance (BHC) and P Sinnett­Jones (MEWRD). Attempted to contact R Owen (University). Purchase of topographic maps. Abstraction of borehol e data for Nyahonbe and adjacent areas. Report writing.

Meeting with R Lambert (WEDC, Loughborough University). Report writing. Visit friends in Harare. JC travels Harare­London.

4. PEOPLE MET

SOUTHERN AFRICA DEVELOPMENT DIVISION (BDDSA)

Andy Tainsh, Agricultural Adviser

BRITISH HIGH COMMISSION

Mrs Joan Laurance, Aid Secretary David Tolson, Assistant Aid Secretary Matthew Streeton, Assistant Aid Secretary

MINISTRY OF LANDS,AGRICULTURE AND RURAL RESETTLEMENT - DEPARTMENT OF RESEARCH AND SPECIALIST SERVICES (DRSS)

Ron Fenner, Director of Research Ivan Anderson, TCO, Soil Chemistry Section Peter Brin, TCO, Soil Chemistry Section

LOWVELD RESEARCH STATION (LRS)

Isaiah Mharapara, Head of Station Matthew Foster, IH Agrohydrology Section Miss Monica Murata, Agronomist

MINISTRY OF ENERGY AND WATER RESOURCES DEVELOPMENT (MEWRD)

Peris Sinnett-Jones, TCO, Adviser and Chief Hydrogeologist Peter Rastall, BGS Contract Driller Marcus Sharpe, TCO, Drilling Adviser

MINISTRY OF LANDS, AGRICULTURE AND RURAL RESETTLEMENT - DEPARTMENT OF RURAL DEVELOPMENT

Mr Gondo, Resettlement Officer, Nyahonbe Resettlement Scheme

LOUGHBOROUGH UNIVERSITY, WEDC GROUP

Bobby Lambert, Pump Engineer

5. COLLECTOR WELL AT CHIREDZI

5.1 Construction

Construction of the well at Chiredzi commenced on 10 February, using four locally employed labourers and one foreman and supervised by the BGS contract driller. The formation consisted of weathered but hard and blocky dolerite, with vertical foliation and joints and many thin quartz veins. The material was harder to dig than might have been expected from the exploratory drill ing, but excellent progress was maintained and water was encountered at 5.2 m. The hole stood open unt il the fi rst Armco lining was inserted when the well had reached 7 m. The well was completed to 12 m on 5 Apri 1 .

5.2 Well Testing

Two pumping tests were carried out on the completed well.

Static water level (bd) Duration of pumping Pump discharge rate Final water level Final drawdown 25% recovery 50% recovery 75% recovery

5.3 Radial Drilling

4 April

5.06 m 90 mins

0.781/sec 5.73 m 0.67 m

!l0 mins 260 mins

18 April

5.33 m 100 mins

5.58 l/sec 12.30 m 6.97 m

195 mins

The radi a 1 dri 11 i ng was carri ed out between 22 and 25 Apri 1. Four 1 ateral s were constructed in order, starting from NE, and then NW, SW and SE. The first is 29 m long and produced an inflow of about 1 l/sec. The second encountered very hard, unbroken rock, was dry and was terminated at 10 m. The third is 30 m long into broken rock with clay and yielded very little water. The last encountered a fault only 1.5 m from the well which produced water inflow. The lateral was completed to 30 m through soft and hard layers of rock with no additional increase in water inflow.

5.4 Collector Well Testing

After the radials have been completed, the standard procedure is to carry out a test in wh i ch the water 1 eve 1 is drawn down to pump suct i on, followed by a longer-term test at a lower pumping rate which simulates the possible operating schedule of the well. The former is compared with the si mil ar test performed on the well before the 1 atera 1 s are constructed, and the latter is used to assess the long-term sustainable yield of the well.

Static water level (bd) Duration of pumping Pump discharge rate Final water level Final drawdown 25% recovery 50% recovery 75% recovery

~

5.38 m 130 mins

5.58 l/sec 12.43 m 7.05 m 69 mins

175 mins 365 mins

Recovery from 12.0 to 10.0 m took 94 minutes, compared to 240 minutes for the same depth interval before the laterals were drilled. This represents an increase in inflow from 0.44 l/sec before the drilling of the laterals to 1.1 l/sec afterwards, a considerable improvement in well performance.

A long-term test was carried out from 9 to 16 May, following a strict daily regime of three two hour pumping periods, separated by three hour rest periods. The pump discharge rate was 0.98 l/sec. Water levels in the neighbouring exploratory boreholes were measured at the beginning and end of each day. Water samples were collected for full chemical analysis close to the beginning and the end of the long-term test.

The well was then completed by installation of a locally-purchased electric centrifugal pump, mounted on a float in the well. The pump is capable of producing 1.2 l/sec, and delivers water to the adjacent irrigation header tank. Final completion works at the well included the installation of a permanent, sturdy access 1 adder and a well cover, comlete with brackets to hold an autographic float water-level recorder. The well-head was completed with a 3 m deep sanitary seal and narrow apron around the well.

During the present visit an additional pumping test was carried out using the permanent pump. The well was pumped for four hours at 1. 23 1/ sec. Autographic recorders were installed on exploratory boreholes 12 and 13 so that detail ed drawdown and recovery measurements coul d be made. Additional water samples were collected for full chemical analysis at BGS.

5.5 Costs

A preliminary estimate of the cost of construction of the well at Chiredzi was given in Robin Herbert's April visit report. Now that the well is completed and operational a complete cost breakdown can be given (in Zimbabwe Dollars).

Local costs of construction:

(a)

(b)

1.

by month:

Month Salaries Diesel Misc Total

Feb 454 367 234 1055 Mar 1334 946 818 3098 Apr 867 713 50 1630 May 74 126 43 243

Totals 2729 2152 1145 6026

by operation:

Well Construction il

Salaries: 1938 Diesel: 1333 Tools & Equipment: 525 Cement: 196 Sand & Gravel: 267 Boots & Hard Hats: 130 Armco lining (12 m @ Z$626/m): 7512

Total Cost of Well Construction: 11930

The personnel involved in the construction of the well comprise four casual 1 abourers at Z$4.85 per day and one foreman at Z$350 per month. The monthly salary bill includes considerable amounts of overtime for working at weekends and on public holidays. Most of the diesel cost is for the use of the MEWRD compressor which was loaned free of charge for thi s work. If a compressor had to be hi red locally, the cost would be Z$25 per hour, which it is estimated would have cost Z$5350. This hire rate is high; for a major development project in which numbers of wells were to be constructed a compressor would be included in the capital items purchased at the beginning of the project. Assuming a life of 10 years, spares at 5% per annum and the construction of 6-8 well s per year for each compressor and an interest rate of 5%, then the present value of the cost of the compressor per well is about one tenth of this, just under Z$500 per well.

2. Short-term Testing and Lateral Drilling

Salaries: Diesel:

il

717 693

Similarly compressor use, if estimated at commercial hire rates, amounted to Z$2700, or Z$300 calculated as above.

3.

4.

Long-term Test

Salaries: Fuel:

.il

74 126

Compressor hire as above, Z$1200 at commercial hire rates and Z$150 for a large project.

Installation of Permanent Pump

Electric pump: 751 Delivery pipes, hoses and fittings: 455 Ladder: 147 Pump float: 182

Total cost of operations 1-4:

1535

16,025

The total cost of the well construction and testing is therefore about Z$14, 500. Th is compares with costs of Z$24, 000 to Z$28, 000 for 2 m diameter wells of brick caisson construction (Table 12.2 of BGS Collector Well Project Report WD/88/31). Detailed costs are not available for the more recent well s at Wenimbi (1 ined with pre-cast concrete segments) or Gutu but it is likely that they were below Z$25,000. In the present example at Chiredzi, just over half (Z$7512) of the total cost of the well is in the imported Armco lining. If suitable material could be obtained locally, then further cost savings might be achieved, and enquiries are being made to establish whether local provision of similar lining segments is technically and economically feasible. The question of collector well costs will be discussed in more detail in the proposed technical report.

A programme of data collection at the well and around the site was prepared, and is included here as Table I.

Consideration will be given now that the well is operating to the need to install a manually operated or animal powered pump. A brief meeting was he 1 din Harare with Bobby Lambert of Loughborough Un i vers ity. His rope and washer pump is now going into commercial production in Harare. The work on development of animal powered pumps at the National Institute of Agricultural Engineering at Hatcliffe (seen on a previous visit) has more or less been abandoned. Peter Rastall, the BGS contract driller, is working on an animal driven diaphragm pump. It was agreed that contact would be maintained with the Loughborough work.

A detailed report on all the hydrogeological work carried out at Chiredzi, from exploratory drilling to the analysis of the pumping tests will be prepared in due course.

6. COLLECTOR WELL SITES FOR ON-FARM TRIALS

A preliminary list of possible general locations for collector well sites in communal lands or resettlement schemes was prepared on the October 1988 vis it, and is repeated here as Table 2 for ease of reference. On the

Table 1

SMALL-SCALE IRRIGATION FROM COLLECTOR WELLS Programme of Hydrogeological Data Collection at Chiredzi

Measurement Frequency By Whom From Remarks Date

Monitoring of during BGS 2/89 Completed; to construction construction be reported

Test pumping completion BGS 5/89 Completed; to of well of well be analysed

and reported

Water levels continuous IH/LRS 6/89 Munro rec in collector weekly well

Well di scharge as operated IH/LRS 6/89 Time log + da i 1 y volume in

tank

EC of well as operated IH/LRS 6/89 discharge weekly at end

of a pumping period

Water levels Every Fri day LRS 10/88 Continues in exp. bhs. on station

Chloride in Aggregate over IH/LRS late 89 Analysis at rainfall month BGS UK

EC of irrig. monthly BGS/IH/LRS 6/89 Km 55.75 canal water mark on

main canal

Full chem. Infrequent BGS 5/89 Analysis at analysis of BGS UK water

Full chem. Infrequent BGS 6/89 Analysis at analysis of BGS UK irrig. canal water + north block tank

Isotopes? ? BGS Analysis at (to be BGS UK considered)

(a) Matibi No. 1 (Neshuru)

(b) Maranda

(c) Ndanga (Zaka)

(d) Sangwe

(e) Ndowoyo

(f) Mutema

(g) Matibi No. 2

(h) Sengwe

(i) Chiswiriswi

(j) Nyahombe

(k) Nyajena

Table 2

Collector Well Sites in Communal lands

location

100-120 km W of LRS

130-140 km W of LRS

80 km N of LRS

60-80 km E of LRS

70-80 km E of LRS

150 km NE of LRS (near Birchenough Bridge)

30-50 km S of LRS

100-120 km S of LRS

30-40 km E of LRS

80 km NW of LRS

80 km NNW of LRS

Underlying Geology

Precambrian basement gneisses

Precambrian basement gneisses

Basement gneisses and granites

Mostly Karoo, some paragneisses

Karoo basa lts

Granite and dolerite

Karoo basa lts

Karoo basalts, ryholites and 1 ater granites

Paragneisses and Karoo

Basement gneisses

Basement gneisses

present visit, two trips were made to the Nyahonbe Resettlement Scheme, located on the Chi redzi - Ngundu road where it crosses the Tokwe Ri ver (Figure 1).

On the first trip, Messrs Chilton and Rastall drove to several of the villages in the scheme to examine their existing water supplies. These are provided by Bush pumps, mounted either on boreholes drilled by the Provi nci a 1 MEWRD offi ce or on wells constructed by the Lutheran Church. The pumps were in varying states of repair; some were not operative and others were being heavily used. It was not possible to gain access to any of the boreholes to measure water levels. The area has considerable topography, with some large inselbergs and generally frequent rock outcrops. There are, however, quite extensive areas of gently sloping land close to most of the villages, which provide the present rain-fed cultivation.

After meet i ng the re sett 1 ement offi cer, Mr Gondo, a vi s it was made to a very new resettlement area on the former Tokwe River Ranch immediately to the north of Nyahonbe, to whi ch people di sp 1 aced by the Mwenez i Dam project are currently being moved. The villages have new boreholes with modified Bush pumps, and access could be gained to measure water levels.

Six boreholes in and near villages 8 and 11 had water levels ranging from 14.9 to 32.1 m; relatively deep and mostly beyond the reach of collector well s.

A second visit was made to Nyahonbe with Messrs. Mharapara, Batchelor and Rastall and Miss Murata. Most of the villages in the scheme were visited, accompanied by the Agritex extension officer for Nyahonbe. Several of the villages expressed considerable interest in developing gardens; some were already growing vegetables in a small way. Villages 5 and 10 were selected as potentially suitable for test drilling.

On return to Harare, the borehole data for the two 1 :50,000 map sheets covering Nyahonde was extracted. Water levels range from 5 to 25 m and most are between 10 and 20 m.

In reporting progress of the project to the BHC (on return to Harare), the issue of on-farm collector wells in the proposed TC project was discussed at some length. It was emphasised by the BHC that a principal objective of the TC project was to test the institutional side of the development of small-scale irrigation from collector wells, and that this should be done in the communal lands rather than the resettlement areas. There are major differences in administrational framework between the two. The resettlement areas are at present outside the District Councils. The Rural Administration Act to bring them together has been passed by parliament but not enacted.

It was agreed, therefore, that efforts to find sites for the on-farm collector wells would be concentrated in the communal lands. Areas for consideration (which were discussed at LRS) include Matibi I, Nyajena and Ndanga (Figure 1). Matibi I includes areas where detailed work was carried out in 1987 in the BGS Basement Aquifer Project, and thi s data will be examined prior to making field visits at the time of the next visit to Zimbabwe.

Figure 1. Location of Areas Visited.

31 °East of '0 Greenwich

7. COLLECTOR WELLS IN ALLUVIUM

A visit was made to Makusia in the Matibi 2 Communal Area immediately to the south of the Lundi River. Makusia is the site of Richard Owen's small irrigated gardens, and was selected during the April visit of Or Robin Herbert as a suitable location for testing techniques of construction of collector wells in alluvial strata.

One of the gardens visited was being very extensively cultivated by the villagers; almost all of the fenced area was currently planted with vegetabl es. The well is equi pped with a Bush pump and appears to give a reliable supply.

At Makusia School there are three boreholes within a few hundred yards of one another. One produces sal ine water and is used for 1 ivestock only, and the handpump on the government borehole has been broken down for some time. Consequently there is a greatly increased demand on the Bush pump installed by Richard Owen; it is being used for domestic water and only a very small fraction of the garden is currently being cultivated. There is a large population around the school and a great need of improved water supplies.

The alluvium at this site extends several hundred metres to a kilometre back from the incised channel of the Lundi, and appears to be relatively deep. The channel itself is several hundred metres across and has steep banks 10-15 m high. This substantial alluvial deposit is present for some distance east-west on both sides of the river. On the north bank, at Hippo Valley Estates, considerable thicknesses of alluvium have been proved by recent exploratory drilling by MEWRO. At the last of these drilling sites, 26 m of alluvium overlies fairly soft Karoo basalt. The alluvium there contains considerable clay down to 15 m and appears to be relatively clean sand from 16 to 26 m.

The alluvial test drilling proposed in April was confirmed. Three holes will be drilled in aline at right angles to the river; additional holes may be required if any of them encounter saline water. The holes will be comp 1 eted as observat i on boreho 1 es, test pumped and water samples taken for return to BGS. If favourable collector well conditions are confirmed, digging will commence immediately, with the agreement of the villagers and the field officer, water at the OA's office in Chiredzi.

8. TC PROPOSAL

The associated TC proposal 'collector wells, small-scale irrigation and dry land ridging' was discussed with BHC and BOOSA. At the beginning of the visit the impression was gained that the POS format document had made its first round of the Zimbabwe Government ministries, was back with BOOSA, and November 1989 was a possible start date. However, on return to Harare, it became cl ear that th is was not the case; the document as revised by Batchelor and Hodgson in January rests with Andy Tainsh at BOOSA for final completion before returning to Harare for submission through the normal channels. The timing of this is not easy to predict, and the project is still therefore some way off.