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The implementation of fog water collection systems in South Africa
Atmospheric Research 64 (2002) 227 – 238 www.elsevier.com/locate/atmos
The implementation of fog water collection systems in South Africa J. Olivier a, C.J. de Rautenbach b,* a
Department of Geography and Environmental Studies, University of South Africa, PO Box 392, UNISA 0003, South Africa b Meteorology, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0002, South Africa Received in revised form 15 February 2002; accepted 22 March 2002
Abstract Two fog water collection systems (FWCS) have been implemented in South Africa. Both are located in areas where communities experience acute water shortages but which are prone to frequent fog episodes. The first was located at a high elevation site at the Tshanowa Junior Primary (JP) School in the Soutpansberg located in the Northern Province and the other near a small rural community at Lepelfontein along the West Coast. The former represents a mountainous site, while the latter is located on a low level coastal plain. The principal aim of the projects was to implement operational FWCSs to supply the communities with water. During the period 1999 to 2001 the total recorded cloud water yields at the Tshanowa JP School and Lepelfontein water collection sites were in the region of 72 422 and 148 691 l, respectively. This is equivalent to just over 2 l m 2 day 1 at the Tshanowa JP School and 4.6 l m 2 day 1 at the Lepelfontein site. Despite the relatively low average daily yields recorded, the total water volume collected on a particular day may be considerable. In fact, at both sites the maximum daily yield exceeded 3800 l. Fog deposition accounted for around 25% and 88% of the total water yield measured at the Tshanowa JP School and Lepelfontein sites, respectively. Both experiments indicated that fog water collection holds considerable potential as an alternative water source in the mountainous regions and along the West Coast of South Africa. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Fog water harvesting; Fog collector; Rainfall harvesting; Unconventional domestic water supply; South Africa
*
Corresponding author. E-mail addresses: [email protected] (J. Olivier), [email protected] (C.J. de Rautenbach).
0169-8095/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 8 0 9 5 ( 0 2 ) 0 0 0 9 4 - 7
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1. Introduction South Africa is an arid country with only 35% of its surface area receiving more than 500 mm rain per year (South African Department of Water Affairs, 1986). Since rainfall decreases from east to west, the West Coast is the most arid of the regions with many places recording annual rainfall totals of 70 mm or less. Few perennial rivers traverse the country and surface water sources are often polluted. In many areas, the groundwater supplies are not only inadequate, but may be contaminated with salts and heavy metals. It has been estimated that five out of every 100 children in rural areas die before the age of five from diseases caused by contaminated water (Huntley et al., 1989). Even in the wetter parts of the country, water is often inaccessible. Water shortages are, thus, a common occurrence in large parts of South Africa, especially in rural areas where people are reliant on rivers and groundwater sources. This situation is aggravated during periods of drought when the water table drops and wells and springs dry up. During the drought of the early 1990s, over 12 million people did not have access to adequate supplies of potable water (South African Department of Water Affairs and Forestry, 1994). Paradoxically, throughout dry periods, fog frequently blankets the mountains along the eastern escarpment and the West Coast littoral zone. Experiments conducted during the 1960s and 1970s in South Africa, and the wellknown fog water collection systems (FWCSs: vertical structures that collect cloud water— fog as well as rain water) erected in Chile, clearly indicated the water harvesting potential of fog (Schutte, 1971; Schemenauer et al., 1988; Schemenauer and Cereceda, 1991, 1992, 1994). The Water Research Commission (WRC) of South Africa funded a research project aimed at determining the feasibility of using fog to supplement rural water supplies in 1995. During the period 1995 to 1998, a number of 1 m2 pilots FWCSs were erected at various sites in the fog-prone parts of South Africa. Recorded water yields indicated that fog water harvesting might be successfully applied in the mountainous parts of the country and along the West Coast, particularly at sites that are exposed to fog bearing winds from the ocean (Olivier and van Heerden, 1999). In 1998, funding was obtained from the South African – Netherlands Research Programme on Alternatives in Development (SANPAD) and the WRC of South Africa to implement two FWCSs. The ultimate aim of each of the projects was to erect a fully operational FWCS in order to supply water to the rural communities. They would serve as a prototype for other cloud water harvesting initiatives. The projects comprised the following aspects: (a) designing, erecting and operating of a FWCS; (b) monitoring water quality and investigating the relationships between various meteorological variables and cloud water yield; and (c) community training and capacity building. This article gives an overview of the selection of the experimental sites, the design of the FWCS, water yields obtained as well as water quality.
2. Site selection Four main factors should be taken into account when determining a suitable site for a FWCS, namely, (a) the potential of collecting large volumes of water, (b) the proximity of
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a water-poor community, (c) accessibility and (d) security. The first two factors are discussed in this paper. 2.1. Water yield potential Water yield depends upon a high fog occurrence, the persistence of fog episodes and the presence of fog bearing winds. During the 1995– 1998 WRC funded project, a comprehensive study of spatial and temporal fog occurrence was conducted to identify areas in South Africa with high fog water potential. The results indicated that the highest water yield along the West Coast occurred at sites with elevations lower than 200 m above Mean Sea Level (MSL) and within 15 km from the coastline. Within this relatively flat coastal zone, sites with higher elevations would obviously receive more water from fog due to the increase in wind speed and moisture content of fog with height. In the mountainous areas, elevation was the most important contributing factor to water yield. A power function was derived to successfully predict yields from elevation values (Olivier and van Heerden, 1999). It was found that fog water collection would only be feasible at elevations of at least 1000 m. Mountainous areas such as the Soutpansberg (translated: Salt Pan Mountains), the mountains forming the eastern escarpment of the country and those in the southwestern Cape Province were thus suitable sites for the implementation of a FWCS. 2.2. Identification of water-poor communities 2.2.1. West Coast The method used to identify and prioritise recipient communities along the West Coast is described in Rush et al. (2000), and comprised, firstly, a comprehensive questionnaire survey of all communities located within a 25-km coastal strip in order to determine the water status of the settlements. Of the 62 communities that responded to the survey, only seven lacked the recommended 25 l per capita per day. These seven communities were prioritised in terms of their location, i.e. distance from the sea and proximity to a suitable water collection site. Lastly, on-site investigations of the three communities with the highest ratings were conducted. Lepelfontein, a small missionary station, was found to be the most suitable site for the implementation of the West Coast fog water project (Olivier and van Heerden, 1999). The village has an altitude of approximately 100 m and is located about 400 km from Cape Town, 70 km to the west of the town Bitterfontein and 5 km from the sea (Fig. 1). The settlement, with its 200 inhabitants, is located at the base of a hill with altitude 200 m above MSL. Although ground water is abundant, it is of such bad quality that it is considered to constitute a health risk. A small solar distillation plant was installed there during 1998 to provide the residents with drinking water. However, very little water is generated implying that most of the water is still transported to the village from elsewhere. 2.2.2. Northern Province In order to identify the recipient community in the mountainous parts of the Northern Province, a list of water-poor communities was obtained from government sources. Those falling within a 25-km zone from a suitable high elevation water collecting site were
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Fig. 1. Geographical locations of (A) the Lepelfontein site along the West Coast and (B) the Tshanowa Junior Primary (JP) School in the Soutpansberg of the Northern Province of South Africa.
identified using topographic maps. A total of 62 communities (comprising 84 270 inhabitants with less than 10 l of water available per person per day) met these criteria. A rating scheme, using indices to reflect the severity of water shortage and the quality of the water and its accessibility was devised to prioritise these communities in terms of water need. In view of the limited funds available, it was decided to limit the operational system to a single FWCS. A short list of suitable communities was then drawn up using the size of the community and its distance from a potential fog water collection site. The final
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selection was made after an on-site examination and discussions with the community leaders. Despite its relatively low elevation, the Tshanowa Junior Primary (JP) School in the Soutpansberg was selected for the implementation project. The school is located at the crest of one of the easternmost promontories of the Soutpansberg in the Northern Province at an elevation of 1004 m above MSL (Fig. 1). A large area of flat vacant land was located immediately adjacent to the school. The site is exposed to fog bearing winds from the east, southeast and northeast. According to the school principal, the area is frequently shrouded in dense fog due to cloud interception. The school population comprises 128 children and four teachers. There are a few houses located near the school but the majority of communities live lower down the mountainside. Although the area has a high rainfall ( > 800 mm) there is no water available at the school. The closest water source is a non-perennial spring located 2 km from the school and a dam situated in the valley more than 5 km away. Although there is a road leading to the school, it is very steep and in poor condition. The rest of the terrain is extremely rugged and steep and it is difficult and time consuming for the inhabitants of the area to obtain sufficient quantities of water for domestic purposes. Moreover, since most water sources in the Northern Province are contaminated with the bilharzias parasite, the quality of the dam water is suspect. In the past, children had to fill bottles at these sources and carry them to school with them.
3. Design and implementation of the FWCSs Permission to erect the two FWCSs was obtained from the relevant local and national authorities and traditional leaders in the vicinity of Lepelfontein and the Tshanowa JP School sites. Construction at the sites commenced in 1999 and local inhabitants were employed to assist with the erection of the FWCSs. The design of both collectors is the same and was based on that used at El Tofo, Chile (Schemenauer et al., 1988; Schemenauer and Cereceda, 1991, 1992) but modified for local conditions (see Fig. 2). Each FWCS consists of three 6-m high wooden poles mounted 9 m apart. Steel cables anchor the system to the ground. Double sets of horizontal steel cables anchor the poles to each other and support the screen. The screen consists of two 9 4 m sections (36 m2 each) of 30% shade cloth netting that were draped over a top cable and threaded through the space between the two middle and the two lower cables. The nets were secured at the lower end by bolting them to sections of perforated steel plates. A gutter was attached to the lower end of the net along the bottom supporting cable. During foggy conditions or rain episodes, water droplets collect on the screen, flow downwards and drip into the gutter. The water is then channelled through a sand filter. This empties into a 1.1 l tipping-bucket connected to an electronic data logger (CR10). From there, it flows through a 40-mm plastic pipe to a 10-kl storage tank located a few meters down slope. Subsequently, two further tanks were erected at the Tshanowa JP School site to collect the overflow from the first. The overflow from the one 10-kl tank at Lepelfontein is used to augment the water from the desalination plant. A complete automatic weather station recoding rainfall, wind speed, wind direction and temperature was installed at each of the cloud water collection sites.
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Fig. 2. Fog water collection system (FWCS) at the Tshanowa Junior Primary (JP) School on the Soutpansberg in the Northern Province of South Africa.
Due to problems encountered with the tipping bucket, a water flow meter was installed in the down pipe at Lepelfontein on 1 June 2000. One of the members of the local community recorded these volumes on an irregular basis. The records were verified by a local farmer and by the team members when visiting the site.
4. Results and analyses 4.1. Water yield Water yields are expressed in terms of the total cloud water yield over a specific period of time. Days on which water was collected are referred to as wet days since the water
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could have been due to either rainfall or fog deposition. In contrast, rain days are defined as days when rainfall was measured using a separate rain gauge while fog days were those days where water was collected but no rainfall was recorded. 4.1.1. West coast During the winter of 1999, hurricane force winds damaged the fog collector at Lepelfontein. This delayed the project implementation by at least 6 months. During the period of September 1999 to September 2001, a total of 36 581 l of water were recorded on the data logger. During this 510-day period, water was collected on 112 days. The mean collection rates were, thus 1.02 l m 2 day 1 or 4.67 l m 2 week day 1. However, the actual volumes collected exceeded this since (a) large gaps occurred in the data logger record and (b) both the data logger and the tipping bucket malfunctioned. Fortunately records from the water flow meter could be used to give more accurate results. Table 1 gives a summary of the monthly water yields collected from the Lepelfontein site during the period June 2000 to September 2001. As a result of higher rainfall, more water was collected during the austral winter months. According to these records, a total of 148 691 l of water flowed into the tank between the beginning of June 2000 and 3 September 2001. During the first period (1 June 2000 to 12 September 2000), the average water collection rate was 369.4 l day 1 or 5.3 l m 2 day 1 while the latter period gave results of 412.2 l day 1 (5.9 l m 2 day 1). Overall, the average daily flow rate was 323 l day 1 or 4.6 l m 2 day 1. 4.1.2. Northern Province In addition to loss of data due to battery failure and problems with the electronic readswitches, further loss of data occurred due to freak weather conditions. In the Soutpansberg, for example, an intense tropical low followed by tropical cyclone Eline wreaked havoc in the northern parts of the country and Mozambique during February 2000. The latter caused widespread devastation that changed streams into torrents, collapsing bridges and washing away the majority of the roads in the mountains. Although an attempt was made to collect the data from the Tshanowa JP School site during this period, roads were impassable until May 2000. Fortunately, the FWCS was not damage by the strong winds during these wet periods. Table 1 Monthly and mean daily fog water yields at the Lepelfontein site along the West Coast Year
Month
Yield (l)
2000 2000 2000 2000 2001 2001 2001 2001 2001 Total
06 07 08 09 03 04 05 07 08
4594 4971 26 629 2225 – 21 292 3501 33 621 15 051 148 691
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The construction of the FWCS was completed on Thursday, 5 March 1999. Since 9 March 1999, water collected by the screen has been consumed on a daily basis by school children and members of the local communities. During the period March 1999 to April 2001, a total of 72 422 l were recorded (Table 2). The actual water volume collected exceeds this value since large gaps occur in the data collection record. Unfortunately, no data were available for the period during which the heaviest rainfall occurred. The largest water volumes were collected during March 1999 (13 035 l) and November 1999 (10 428 l). Since the number of people utilizing the collected water is not known, it is not possible to give water consumption rates in terms of litre per capita per day. Instead, water yields are simply expressed in terms of litres. The highest mean daily and wet day yields were recorded during June 2000 (9.3 l m 2 day 1 and 2007 l m 2 week day 1). The highest daily yields were recorded on 5 June 2000 and 20 November 1999 when 3883 and 3179 l of water were collected, respectively. Water yields of more than 1000 l were recorded on 17 other occasions. Hourly values in excess of 500 l were collected between 01:00 and 02:00 on 24 March 1999 and between 09:00 and 10:00 on 20 November 1999. The average collection rate during the total recorded period was just above 2 l m 2 day 1. 4.2. Characteristic of water collection episodes 4.2.1. Contribution of rainfall vs. fog In order to determine the contribution of fog relative to the total cloud water yield, hourly cloud water and rainfall data were analysed. It was assumed that whenever rain was
Table 2 Monthly and mean daily fog water yields at the Tshanowa Junior Primary (JP) School in the Soutpansberg of the Northern Province Year
Month
Yield (l)
l day
1999 1999 1999 1999 1999 1999 1999 1999 1999 1999 2000 2000 2000 2000 2000 2001 2001 2001 2001 Total
03 04 05 06 07 08 09 10 11 12 05 06 10 11 12 01 02 03 04
13 035.0 566.5 4834.5 3492.5 6688.0 3674.0 2937.0 2656.5 10 428.0 368.5 51.5 8029.0 1168.0 2730.0 1505.0 685.0 6829.0 877.0 877.0 72 422.0
465.5 188.8 201.4 120.4 230.6 118.5 133.5 132.8 347.6 61.4 4.3 699.1 48.7 91.0 48.6 22.1 243.9 48.7 48.7 156.8
1
l week day 566.7 188.9 690.6 582.1 455.9 734.8 489.5 295.2 548.8 92.1 17.3 2007.3 83.4 143.7 94.1 45.7 284.5 73.1 73.1 251.5
1
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recorded by the rain gauge, all the water deposited on the collector originated exclusively from rainfall. On the other hand, if no rain was recorded, all the water collected was assumed to originate from fog alone. Although this technique underestimates the contribution by fog, it does give some indication of the relative contributions of fog and rainfall to the total volume of water collected. Hourly cloud water records were compared with the corresponding rain gauge measurements in order to distinguish between ‘‘rain hours’’ and ‘‘fog hours’’. The volume of water collected during each of these two sub-sets were summed to obtain daily and monthly totals. Unfortunately, the water flow meter records for Lepelfontein did not show hourly data, the tipping bucket data were used. It was assumed that the errors and undercounts would apply equally to rain hours and to fog hours. Rainfall records were only available from January 2001, hence the values for Lepelfontein span the period 1 January to 3 September 2001. Table 3 gives a summary of the contribution of fog to the total volumes collected. It was found that, at the Tshanowa JP School site, around 25% of the cloud water yields was due to fog alone, while at Lepelfontein, it made up at least 88% of the total yield. 4.2.2. Diurnal incidence At the Tshanowa JP School and Lepelfontein sites, most water was collected during the early morning hours, notably between 02:00 and 09:00. At the school, a wet episode usually commenced with a period during which fog alone occurred, followed by the rain event and ending again with a foggy period. Deposition occurring between 21:00 and 06:00 was mostly due to fog while water from rain made up the largest part of the total yield during the daylight hours. At Lepelfontein, rainfall occurred at any time during the day while deposition due to fog was confined to the early morning. 4.2.3. Synoptic controls Synoptic charts and wind directions were analysed for wet events to determine the dominant synoptic-scale controls associated with the deposition of water at the two experimental sites. It was found that most deposition at the Tshanowa JP School occurred with winds from the southeasterly quadrant—specifically those with a bearing of 135j to Table 3 Monthly rainfall totals (mm) with the corresponding percentage of water yield attributed to fog water alone Tshanowa Junior Primary (JP) School
Lepelfontein
Year
Month
Rainfall (mm)
% Fog
Year
Month
1999 1999 1999 2000 2000 2000 2001 2001 2001 2001 Mean
10 11 12 10 11 12 01 02 03 04
61.3 201.2 97.5 48.9 119.9 56.7 24.2 392.2 78.8 36.7 1056.1
46.0 16.0 62.7 47.3 27.9 42.2 52.0 13.2 36.5 41.3 24.5
2001 2001 2001 2001 2001 2001 2001
01 03 04 05 06 07 08
Mean
Rainfall (mm)
% Fog
3.0 9.0 23.0 35.5 8.0 – 50.0
92.6 90.6 91.0 87.8 100.0 0.0 68.2
>130.0
87.9
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151j. The major synoptic conditions associated with these episode were an anticyclone located off the South African east coast, manifest either as the Indian Ocean High or as a ridging Atlantic high. A tropical low over the southern Mozambique Channel probably contributed to an onshore flow of moist air from the east (Fig. 3). Along the West Coast, fog deposition is mostly associated with onshore breezes originating either from the South Atlantic anticyclone located relatively far to the south of the continent or from north westerly and westerly winds on the northern perimeter of a coastal low. Rainfall is normally associated with a passing cold front. Fig. 3 illustrates typical synoptic situations that are conducive to the simultaneous collection of cloud water at the Tshanowa JP School and Lepelfontein sites. 4.3. Water quality Table 4 shows the results of the chemical and microbial analyses of water collected at the Tshanowa JP School and Lepelfontein sites. Water collected at the Tshanowa JP School was very pure having very low concentrations of sulphates, chlorides, dissolved calcium, magnesium, sodium and potassium. No iron, manganese or nitrates are present. As expected, no disease-forming bacteria were present in the water. The few heterotrophic
Fig. 3. Sea level pressure isobars (hPa) of a typical synoptic scale condition that is suitable for moisture advection from the Atlantic and Indian Oceans towards both the Tshanowa Junior Primary (JP) School and Lepelfontein fog water collection sites (sites located in the shaded areas). The arrows denote the general direction of the wind.
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Table 4 Chemical analyses of fog water at the Tshanowa Junior Primary (JP) School and Lepelfontein sites Tshanowa, 21 August 2001 Analyses pH TDS (mg l 1) SO4 (mg l 1) NO3:N (mg l 1) Cl (mg l 1) F (mg l 1) CO3 HCO3 Ca (mg l 1) Mg (mg l 1) Na (mg l 1) K (mg l 1) Fe (mg l 1) Mn (mg l 1) Sum Cations (me l Sum Anions (me l
1
) )
1
Microbial analyses Total viable organisms (ml 1) Total Coliform organisms 100 (ml 1) Faecal Coliform organisms 100 (ml 1)
Lepelfontein, 18 September 2000
5.9 37.0 2.90 0.0 8.9 0.01 0.0 15.4 2.7 3.1 3.4 1.09 0.0 0.0 0.56 0.57
7.23 188.0 23.3 7.77 35.7 0.06 0.0 56.5 14.0 11.8 26.4 2.47 0.0 0.0 2.89 2.98
6 <1 <1
4 <1 <1
bacteria present in the sample merely reflected those occurring naturally in the atmosphere. Hence, according to the guidelines laid down for the assessment of the quality of domestic water supplies, by the South African Department of Water Affairs and Forestry, the Department of Health and the WRC, the water obtained at the at the Tshanowa JP School was classified as Class 0 (ideal water quality). Water samples at Lepelfontein were collected from the 10-kl tank. Initially, they showed relatively high concentrations of sodium, chloride and bicarbonate ions. These may have been due to the proximity of the ocean and wind blow spray. It is also possible that some contamination from local water supplies could have occurred during the construction phase. However, later samples show a marked improvement in water quality (Table 4). According to World Health Organization (WHO) standards, the water at both sites was found to be suitable for human consumption.
5. Discussion and conclusions The results indicate that in terms of both quality and magnitude of yield—cloud water harvesting could be used successfully to supplement water supplies in the fog prone regions of the country. However, care must be taken to select a suitable site and to ensure that the orientation of the collector is perpendicular to the direction of fog bearing winds. Ideally, the site should be exposed to frequent fog bearing winds and, in the mountainous
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areas, have an elevation in excess of 1000 m. Sites in many parts of South Africa have elevations of more than 2000 m. According to experiments conducted previously, such sites could obtain yields of more than four times the volumes recorded at the Tshanowa JP School (Schutte, 1971; Olivier and van Heerden, 1999). An ideal West Coast water collection site would be on the crest of a hill, with an altitude of between 200 and 700 m above MSL, within 5 km of the sea. For the optimal utilization of this water source, wastage would have to be eliminated. At present, the last tank at the Tshanowa JP School site overflows regularly and water is lost. It is envisaged that if sufficient funds can be obtained—a series of water tanks will be erected. Excess water, not required for domestic purposes, will be used to establish community gardens. This should enhance the quality of life of recipient communities to a considerable extent.
Acknowledgements We wish to thank the WRC and SANPAD for their financial support, the principal of the Tshanowa JP school in the Soutpansberg, Mr. Netshifhefhe, and the traditional leader, Mr. Vondo for their assistance throughout the Soutpansberg project. Also many thanks to Mr. P. Rossouw and Jossie for their assistance at the Lepelfontein project and to Prof. J. van Heerden for the construction of the FWCSs and data collection.
References Huntley, B.J., Siegfried, R., Sunter, C., 1989. South African Environments into the 21st Century (Tafelberg, Cape Town). Olivier, J., van Heerden, J., 1999. The South African Fog Water Collection Project. WRC Report No. 671/1/99. Water Research Commission, Pretoria. Rush, K., van Huyssteen, M.K.R., Olivier, J., 2000. Patterns of domestic water inadequacy on the South African West Coast. Water S.A. 26 (4), 537 – 554. Schemenauer, R.S., Cereceda, P., 1991. Fog water collection in arid coastal locations. Ambio 20, 303 – 308. Schemenauer, R.S., Cereceda, P., 1992. Water from fog-covered mountains. Waterlines 10, 275 – 290. Schemenauer, R.S., Cereceda, P., 1994. Fog collection’s role in water planning for developing countries. Natural Resources Forum 18 (2), 91 – 100. Schemenauer, R.S., Fuenzalida, H., Cereceda, P., 1988. A neglected water resource: the Camanchaca of South America. Bulletin of the American Meteorological Society 69, 138 – 147. Schutte, J.M., 1971. Die onttrekking van water uit die lae wolke op Mariepskop. Technical note no. 20, Division of Hydrological Research, South African Department of Water Affairs, Pretoria. South African Department of Water Affairs, 1986. Management of Water Resources of the Republic of South Africa. Department of Water Affairs, Pretoria. South African Department of Water Affairs and Forestry, 1994. Water Supply and Sanitation Policy. White Paper. Government Printer, Pretoria.
The implementation of fog water collection systems in South Africa J. Olivier a, C.J. de Rautenbach b,* a
Department of Geography and Environmental Studies, University of South Africa, PO Box 392, UNISA 0003, South Africa b Meteorology, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0002, South Africa Received in revised form 15 February 2002; accepted 22 March 2002
Abstract Two fog water collection systems (FWCS) have been implemented in South Africa. Both are located in areas where communities experience acute water shortages but which are prone to frequent fog episodes. The first was located at a high elevation site at the Tshanowa Junior Primary (JP) School in the Soutpansberg located in the Northern Province and the other near a small rural community at Lepelfontein along the West Coast. The former represents a mountainous site, while the latter is located on a low level coastal plain. The principal aim of the projects was to implement operational FWCSs to supply the communities with water. During the period 1999 to 2001 the total recorded cloud water yields at the Tshanowa JP School and Lepelfontein water collection sites were in the region of 72 422 and 148 691 l, respectively. This is equivalent to just over 2 l m 2 day 1 at the Tshanowa JP School and 4.6 l m 2 day 1 at the Lepelfontein site. Despite the relatively low average daily yields recorded, the total water volume collected on a particular day may be considerable. In fact, at both sites the maximum daily yield exceeded 3800 l. Fog deposition accounted for around 25% and 88% of the total water yield measured at the Tshanowa JP School and Lepelfontein sites, respectively. Both experiments indicated that fog water collection holds considerable potential as an alternative water source in the mountainous regions and along the West Coast of South Africa. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Fog water harvesting; Fog collector; Rainfall harvesting; Unconventional domestic water supply; South Africa
*
Corresponding author. E-mail addresses: [email protected] (J. Olivier), [email protected] (C.J. de Rautenbach).
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1. Introduction South Africa is an arid country with only 35% of its surface area receiving more than 500 mm rain per year (South African Department of Water Affairs, 1986). Since rainfall decreases from east to west, the West Coast is the most arid of the regions with many places recording annual rainfall totals of 70 mm or less. Few perennial rivers traverse the country and surface water sources are often polluted. In many areas, the groundwater supplies are not only inadequate, but may be contaminated with salts and heavy metals. It has been estimated that five out of every 100 children in rural areas die before the age of five from diseases caused by contaminated water (Huntley et al., 1989). Even in the wetter parts of the country, water is often inaccessible. Water shortages are, thus, a common occurrence in large parts of South Africa, especially in rural areas where people are reliant on rivers and groundwater sources. This situation is aggravated during periods of drought when the water table drops and wells and springs dry up. During the drought of the early 1990s, over 12 million people did not have access to adequate supplies of potable water (South African Department of Water Affairs and Forestry, 1994). Paradoxically, throughout dry periods, fog frequently blankets the mountains along the eastern escarpment and the West Coast littoral zone. Experiments conducted during the 1960s and 1970s in South Africa, and the wellknown fog water collection systems (FWCSs: vertical structures that collect cloud water— fog as well as rain water) erected in Chile, clearly indicated the water harvesting potential of fog (Schutte, 1971; Schemenauer et al., 1988; Schemenauer and Cereceda, 1991, 1992, 1994). The Water Research Commission (WRC) of South Africa funded a research project aimed at determining the feasibility of using fog to supplement rural water supplies in 1995. During the period 1995 to 1998, a number of 1 m2 pilots FWCSs were erected at various sites in the fog-prone parts of South Africa. Recorded water yields indicated that fog water harvesting might be successfully applied in the mountainous parts of the country and along the West Coast, particularly at sites that are exposed to fog bearing winds from the ocean (Olivier and van Heerden, 1999). In 1998, funding was obtained from the South African – Netherlands Research Programme on Alternatives in Development (SANPAD) and the WRC of South Africa to implement two FWCSs. The ultimate aim of each of the projects was to erect a fully operational FWCS in order to supply water to the rural communities. They would serve as a prototype for other cloud water harvesting initiatives. The projects comprised the following aspects: (a) designing, erecting and operating of a FWCS; (b) monitoring water quality and investigating the relationships between various meteorological variables and cloud water yield; and (c) community training and capacity building. This article gives an overview of the selection of the experimental sites, the design of the FWCS, water yields obtained as well as water quality.
2. Site selection Four main factors should be taken into account when determining a suitable site for a FWCS, namely, (a) the potential of collecting large volumes of water, (b) the proximity of
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a water-poor community, (c) accessibility and (d) security. The first two factors are discussed in this paper. 2.1. Water yield potential Water yield depends upon a high fog occurrence, the persistence of fog episodes and the presence of fog bearing winds. During the 1995– 1998 WRC funded project, a comprehensive study of spatial and temporal fog occurrence was conducted to identify areas in South Africa with high fog water potential. The results indicated that the highest water yield along the West Coast occurred at sites with elevations lower than 200 m above Mean Sea Level (MSL) and within 15 km from the coastline. Within this relatively flat coastal zone, sites with higher elevations would obviously receive more water from fog due to the increase in wind speed and moisture content of fog with height. In the mountainous areas, elevation was the most important contributing factor to water yield. A power function was derived to successfully predict yields from elevation values (Olivier and van Heerden, 1999). It was found that fog water collection would only be feasible at elevations of at least 1000 m. Mountainous areas such as the Soutpansberg (translated: Salt Pan Mountains), the mountains forming the eastern escarpment of the country and those in the southwestern Cape Province were thus suitable sites for the implementation of a FWCS. 2.2. Identification of water-poor communities 2.2.1. West Coast The method used to identify and prioritise recipient communities along the West Coast is described in Rush et al. (2000), and comprised, firstly, a comprehensive questionnaire survey of all communities located within a 25-km coastal strip in order to determine the water status of the settlements. Of the 62 communities that responded to the survey, only seven lacked the recommended 25 l per capita per day. These seven communities were prioritised in terms of their location, i.e. distance from the sea and proximity to a suitable water collection site. Lastly, on-site investigations of the three communities with the highest ratings were conducted. Lepelfontein, a small missionary station, was found to be the most suitable site for the implementation of the West Coast fog water project (Olivier and van Heerden, 1999). The village has an altitude of approximately 100 m and is located about 400 km from Cape Town, 70 km to the west of the town Bitterfontein and 5 km from the sea (Fig. 1). The settlement, with its 200 inhabitants, is located at the base of a hill with altitude 200 m above MSL. Although ground water is abundant, it is of such bad quality that it is considered to constitute a health risk. A small solar distillation plant was installed there during 1998 to provide the residents with drinking water. However, very little water is generated implying that most of the water is still transported to the village from elsewhere. 2.2.2. Northern Province In order to identify the recipient community in the mountainous parts of the Northern Province, a list of water-poor communities was obtained from government sources. Those falling within a 25-km zone from a suitable high elevation water collecting site were
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Fig. 1. Geographical locations of (A) the Lepelfontein site along the West Coast and (B) the Tshanowa Junior Primary (JP) School in the Soutpansberg of the Northern Province of South Africa.
identified using topographic maps. A total of 62 communities (comprising 84 270 inhabitants with less than 10 l of water available per person per day) met these criteria. A rating scheme, using indices to reflect the severity of water shortage and the quality of the water and its accessibility was devised to prioritise these communities in terms of water need. In view of the limited funds available, it was decided to limit the operational system to a single FWCS. A short list of suitable communities was then drawn up using the size of the community and its distance from a potential fog water collection site. The final
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selection was made after an on-site examination and discussions with the community leaders. Despite its relatively low elevation, the Tshanowa Junior Primary (JP) School in the Soutpansberg was selected for the implementation project. The school is located at the crest of one of the easternmost promontories of the Soutpansberg in the Northern Province at an elevation of 1004 m above MSL (Fig. 1). A large area of flat vacant land was located immediately adjacent to the school. The site is exposed to fog bearing winds from the east, southeast and northeast. According to the school principal, the area is frequently shrouded in dense fog due to cloud interception. The school population comprises 128 children and four teachers. There are a few houses located near the school but the majority of communities live lower down the mountainside. Although the area has a high rainfall ( > 800 mm) there is no water available at the school. The closest water source is a non-perennial spring located 2 km from the school and a dam situated in the valley more than 5 km away. Although there is a road leading to the school, it is very steep and in poor condition. The rest of the terrain is extremely rugged and steep and it is difficult and time consuming for the inhabitants of the area to obtain sufficient quantities of water for domestic purposes. Moreover, since most water sources in the Northern Province are contaminated with the bilharzias parasite, the quality of the dam water is suspect. In the past, children had to fill bottles at these sources and carry them to school with them.
3. Design and implementation of the FWCSs Permission to erect the two FWCSs was obtained from the relevant local and national authorities and traditional leaders in the vicinity of Lepelfontein and the Tshanowa JP School sites. Construction at the sites commenced in 1999 and local inhabitants were employed to assist with the erection of the FWCSs. The design of both collectors is the same and was based on that used at El Tofo, Chile (Schemenauer et al., 1988; Schemenauer and Cereceda, 1991, 1992) but modified for local conditions (see Fig. 2). Each FWCS consists of three 6-m high wooden poles mounted 9 m apart. Steel cables anchor the system to the ground. Double sets of horizontal steel cables anchor the poles to each other and support the screen. The screen consists of two 9 4 m sections (36 m2 each) of 30% shade cloth netting that were draped over a top cable and threaded through the space between the two middle and the two lower cables. The nets were secured at the lower end by bolting them to sections of perforated steel plates. A gutter was attached to the lower end of the net along the bottom supporting cable. During foggy conditions or rain episodes, water droplets collect on the screen, flow downwards and drip into the gutter. The water is then channelled through a sand filter. This empties into a 1.1 l tipping-bucket connected to an electronic data logger (CR10). From there, it flows through a 40-mm plastic pipe to a 10-kl storage tank located a few meters down slope. Subsequently, two further tanks were erected at the Tshanowa JP School site to collect the overflow from the first. The overflow from the one 10-kl tank at Lepelfontein is used to augment the water from the desalination plant. A complete automatic weather station recoding rainfall, wind speed, wind direction and temperature was installed at each of the cloud water collection sites.
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Fig. 2. Fog water collection system (FWCS) at the Tshanowa Junior Primary (JP) School on the Soutpansberg in the Northern Province of South Africa.
Due to problems encountered with the tipping bucket, a water flow meter was installed in the down pipe at Lepelfontein on 1 June 2000. One of the members of the local community recorded these volumes on an irregular basis. The records were verified by a local farmer and by the team members when visiting the site.
4. Results and analyses 4.1. Water yield Water yields are expressed in terms of the total cloud water yield over a specific period of time. Days on which water was collected are referred to as wet days since the water
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could have been due to either rainfall or fog deposition. In contrast, rain days are defined as days when rainfall was measured using a separate rain gauge while fog days were those days where water was collected but no rainfall was recorded. 4.1.1. West coast During the winter of 1999, hurricane force winds damaged the fog collector at Lepelfontein. This delayed the project implementation by at least 6 months. During the period of September 1999 to September 2001, a total of 36 581 l of water were recorded on the data logger. During this 510-day period, water was collected on 112 days. The mean collection rates were, thus 1.02 l m 2 day 1 or 4.67 l m 2 week day 1. However, the actual volumes collected exceeded this since (a) large gaps occurred in the data logger record and (b) both the data logger and the tipping bucket malfunctioned. Fortunately records from the water flow meter could be used to give more accurate results. Table 1 gives a summary of the monthly water yields collected from the Lepelfontein site during the period June 2000 to September 2001. As a result of higher rainfall, more water was collected during the austral winter months. According to these records, a total of 148 691 l of water flowed into the tank between the beginning of June 2000 and 3 September 2001. During the first period (1 June 2000 to 12 September 2000), the average water collection rate was 369.4 l day 1 or 5.3 l m 2 day 1 while the latter period gave results of 412.2 l day 1 (5.9 l m 2 day 1). Overall, the average daily flow rate was 323 l day 1 or 4.6 l m 2 day 1. 4.1.2. Northern Province In addition to loss of data due to battery failure and problems with the electronic readswitches, further loss of data occurred due to freak weather conditions. In the Soutpansberg, for example, an intense tropical low followed by tropical cyclone Eline wreaked havoc in the northern parts of the country and Mozambique during February 2000. The latter caused widespread devastation that changed streams into torrents, collapsing bridges and washing away the majority of the roads in the mountains. Although an attempt was made to collect the data from the Tshanowa JP School site during this period, roads were impassable until May 2000. Fortunately, the FWCS was not damage by the strong winds during these wet periods. Table 1 Monthly and mean daily fog water yields at the Lepelfontein site along the West Coast Year
Month
Yield (l)
2000 2000 2000 2000 2001 2001 2001 2001 2001 Total
06 07 08 09 03 04 05 07 08
4594 4971 26 629 2225 – 21 292 3501 33 621 15 051 148 691
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The construction of the FWCS was completed on Thursday, 5 March 1999. Since 9 March 1999, water collected by the screen has been consumed on a daily basis by school children and members of the local communities. During the period March 1999 to April 2001, a total of 72 422 l were recorded (Table 2). The actual water volume collected exceeds this value since large gaps occur in the data collection record. Unfortunately, no data were available for the period during which the heaviest rainfall occurred. The largest water volumes were collected during March 1999 (13 035 l) and November 1999 (10 428 l). Since the number of people utilizing the collected water is not known, it is not possible to give water consumption rates in terms of litre per capita per day. Instead, water yields are simply expressed in terms of litres. The highest mean daily and wet day yields were recorded during June 2000 (9.3 l m 2 day 1 and 2007 l m 2 week day 1). The highest daily yields were recorded on 5 June 2000 and 20 November 1999 when 3883 and 3179 l of water were collected, respectively. Water yields of more than 1000 l were recorded on 17 other occasions. Hourly values in excess of 500 l were collected between 01:00 and 02:00 on 24 March 1999 and between 09:00 and 10:00 on 20 November 1999. The average collection rate during the total recorded period was just above 2 l m 2 day 1. 4.2. Characteristic of water collection episodes 4.2.1. Contribution of rainfall vs. fog In order to determine the contribution of fog relative to the total cloud water yield, hourly cloud water and rainfall data were analysed. It was assumed that whenever rain was
Table 2 Monthly and mean daily fog water yields at the Tshanowa Junior Primary (JP) School in the Soutpansberg of the Northern Province Year
Month
Yield (l)
l day
1999 1999 1999 1999 1999 1999 1999 1999 1999 1999 2000 2000 2000 2000 2000 2001 2001 2001 2001 Total
03 04 05 06 07 08 09 10 11 12 05 06 10 11 12 01 02 03 04
13 035.0 566.5 4834.5 3492.5 6688.0 3674.0 2937.0 2656.5 10 428.0 368.5 51.5 8029.0 1168.0 2730.0 1505.0 685.0 6829.0 877.0 877.0 72 422.0
465.5 188.8 201.4 120.4 230.6 118.5 133.5 132.8 347.6 61.4 4.3 699.1 48.7 91.0 48.6 22.1 243.9 48.7 48.7 156.8
1
l week day 566.7 188.9 690.6 582.1 455.9 734.8 489.5 295.2 548.8 92.1 17.3 2007.3 83.4 143.7 94.1 45.7 284.5 73.1 73.1 251.5
1
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recorded by the rain gauge, all the water deposited on the collector originated exclusively from rainfall. On the other hand, if no rain was recorded, all the water collected was assumed to originate from fog alone. Although this technique underestimates the contribution by fog, it does give some indication of the relative contributions of fog and rainfall to the total volume of water collected. Hourly cloud water records were compared with the corresponding rain gauge measurements in order to distinguish between ‘‘rain hours’’ and ‘‘fog hours’’. The volume of water collected during each of these two sub-sets were summed to obtain daily and monthly totals. Unfortunately, the water flow meter records for Lepelfontein did not show hourly data, the tipping bucket data were used. It was assumed that the errors and undercounts would apply equally to rain hours and to fog hours. Rainfall records were only available from January 2001, hence the values for Lepelfontein span the period 1 January to 3 September 2001. Table 3 gives a summary of the contribution of fog to the total volumes collected. It was found that, at the Tshanowa JP School site, around 25% of the cloud water yields was due to fog alone, while at Lepelfontein, it made up at least 88% of the total yield. 4.2.2. Diurnal incidence At the Tshanowa JP School and Lepelfontein sites, most water was collected during the early morning hours, notably between 02:00 and 09:00. At the school, a wet episode usually commenced with a period during which fog alone occurred, followed by the rain event and ending again with a foggy period. Deposition occurring between 21:00 and 06:00 was mostly due to fog while water from rain made up the largest part of the total yield during the daylight hours. At Lepelfontein, rainfall occurred at any time during the day while deposition due to fog was confined to the early morning. 4.2.3. Synoptic controls Synoptic charts and wind directions were analysed for wet events to determine the dominant synoptic-scale controls associated with the deposition of water at the two experimental sites. It was found that most deposition at the Tshanowa JP School occurred with winds from the southeasterly quadrant—specifically those with a bearing of 135j to Table 3 Monthly rainfall totals (mm) with the corresponding percentage of water yield attributed to fog water alone Tshanowa Junior Primary (JP) School
Lepelfontein
Year
Month
Rainfall (mm)
% Fog
Year
Month
1999 1999 1999 2000 2000 2000 2001 2001 2001 2001 Mean
10 11 12 10 11 12 01 02 03 04
61.3 201.2 97.5 48.9 119.9 56.7 24.2 392.2 78.8 36.7 1056.1
46.0 16.0 62.7 47.3 27.9 42.2 52.0 13.2 36.5 41.3 24.5
2001 2001 2001 2001 2001 2001 2001
01 03 04 05 06 07 08
Mean
Rainfall (mm)
% Fog
3.0 9.0 23.0 35.5 8.0 – 50.0
92.6 90.6 91.0 87.8 100.0 0.0 68.2
>130.0
87.9
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151j. The major synoptic conditions associated with these episode were an anticyclone located off the South African east coast, manifest either as the Indian Ocean High or as a ridging Atlantic high. A tropical low over the southern Mozambique Channel probably contributed to an onshore flow of moist air from the east (Fig. 3). Along the West Coast, fog deposition is mostly associated with onshore breezes originating either from the South Atlantic anticyclone located relatively far to the south of the continent or from north westerly and westerly winds on the northern perimeter of a coastal low. Rainfall is normally associated with a passing cold front. Fig. 3 illustrates typical synoptic situations that are conducive to the simultaneous collection of cloud water at the Tshanowa JP School and Lepelfontein sites. 4.3. Water quality Table 4 shows the results of the chemical and microbial analyses of water collected at the Tshanowa JP School and Lepelfontein sites. Water collected at the Tshanowa JP School was very pure having very low concentrations of sulphates, chlorides, dissolved calcium, magnesium, sodium and potassium. No iron, manganese or nitrates are present. As expected, no disease-forming bacteria were present in the water. The few heterotrophic
Fig. 3. Sea level pressure isobars (hPa) of a typical synoptic scale condition that is suitable for moisture advection from the Atlantic and Indian Oceans towards both the Tshanowa Junior Primary (JP) School and Lepelfontein fog water collection sites (sites located in the shaded areas). The arrows denote the general direction of the wind.
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Table 4 Chemical analyses of fog water at the Tshanowa Junior Primary (JP) School and Lepelfontein sites Tshanowa, 21 August 2001 Analyses pH TDS (mg l 1) SO4 (mg l 1) NO3:N (mg l 1) Cl (mg l 1) F (mg l 1) CO3 HCO3 Ca (mg l 1) Mg (mg l 1) Na (mg l 1) K (mg l 1) Fe (mg l 1) Mn (mg l 1) Sum Cations (me l Sum Anions (me l
1
) )
1
Microbial analyses Total viable organisms (ml 1) Total Coliform organisms 100 (ml 1) Faecal Coliform organisms 100 (ml 1)
Lepelfontein, 18 September 2000
5.9 37.0 2.90 0.0 8.9 0.01 0.0 15.4 2.7 3.1 3.4 1.09 0.0 0.0 0.56 0.57
7.23 188.0 23.3 7.77 35.7 0.06 0.0 56.5 14.0 11.8 26.4 2.47 0.0 0.0 2.89 2.98
6 <1 <1
4 <1 <1
bacteria present in the sample merely reflected those occurring naturally in the atmosphere. Hence, according to the guidelines laid down for the assessment of the quality of domestic water supplies, by the South African Department of Water Affairs and Forestry, the Department of Health and the WRC, the water obtained at the at the Tshanowa JP School was classified as Class 0 (ideal water quality). Water samples at Lepelfontein were collected from the 10-kl tank. Initially, they showed relatively high concentrations of sodium, chloride and bicarbonate ions. These may have been due to the proximity of the ocean and wind blow spray. It is also possible that some contamination from local water supplies could have occurred during the construction phase. However, later samples show a marked improvement in water quality (Table 4). According to World Health Organization (WHO) standards, the water at both sites was found to be suitable for human consumption.
5. Discussion and conclusions The results indicate that in terms of both quality and magnitude of yield—cloud water harvesting could be used successfully to supplement water supplies in the fog prone regions of the country. However, care must be taken to select a suitable site and to ensure that the orientation of the collector is perpendicular to the direction of fog bearing winds. Ideally, the site should be exposed to frequent fog bearing winds and, in the mountainous
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areas, have an elevation in excess of 1000 m. Sites in many parts of South Africa have elevations of more than 2000 m. According to experiments conducted previously, such sites could obtain yields of more than four times the volumes recorded at the Tshanowa JP School (Schutte, 1971; Olivier and van Heerden, 1999). An ideal West Coast water collection site would be on the crest of a hill, with an altitude of between 200 and 700 m above MSL, within 5 km of the sea. For the optimal utilization of this water source, wastage would have to be eliminated. At present, the last tank at the Tshanowa JP School site overflows regularly and water is lost. It is envisaged that if sufficient funds can be obtained—a series of water tanks will be erected. Excess water, not required for domestic purposes, will be used to establish community gardens. This should enhance the quality of life of recipient communities to a considerable extent.
Acknowledgements We wish to thank the WRC and SANPAD for their financial support, the principal of the Tshanowa JP school in the Soutpansberg, Mr. Netshifhefhe, and the traditional leader, Mr. Vondo for their assistance throughout the Soutpansberg project. Also many thanks to Mr. P. Rossouw and Jossie for their assistance at the Lepelfontein project and to Prof. J. van Heerden for the construction of the FWCSs and data collection.
References Huntley, B.J., Siegfried, R., Sunter, C., 1989. South African Environments into the 21st Century (Tafelberg, Cape Town). Olivier, J., van Heerden, J., 1999. The South African Fog Water Collection Project. WRC Report No. 671/1/99. Water Research Commission, Pretoria. Rush, K., van Huyssteen, M.K.R., Olivier, J., 2000. Patterns of domestic water inadequacy on the South African West Coast. Water S.A. 26 (4), 537 – 554. Schemenauer, R.S., Cereceda, P., 1991. Fog water collection in arid coastal locations. Ambio 20, 303 – 308. Schemenauer, R.S., Cereceda, P., 1992. Water from fog-covered mountains. Waterlines 10, 275 – 290. Schemenauer, R.S., Cereceda, P., 1994. Fog collection’s role in water planning for developing countries. Natural Resources Forum 18 (2), 91 – 100. Schemenauer, R.S., Fuenzalida, H., Cereceda, P., 1988. A neglected water resource: the Camanchaca of South America. Bulletin of the American Meteorological Society 69, 138 – 147. Schutte, J.M., 1971. Die onttrekking van water uit die lae wolke op Mariepskop. Technical note no. 20, Division of Hydrological Research, South African Department of Water Affairs, Pretoria. South African Department of Water Affairs, 1986. Management of Water Resources of the Republic of South Africa. Department of Water Affairs, Pretoria. South African Department of Water Affairs and Forestry, 1994. Water Supply and Sanitation Policy. White Paper. Government Printer, Pretoria.