A few figures are enough to demonstrate the significant economic benefits that can result from even a small improvement in exploiting rainfall. In Cape Town's Wemmershoek catchment the rainfall during the reservoir's hold-over period, a three dry-year cycle, is estimated at about 60 in. The available run-off for supply however is only 25 in. Approximately 35 in. are lost by evaporation and transpiration, and possibly percolation. To obtain the 25 in. of yield, an expenditure of 8,000,000 was incurred, i.e. about 300,000 per in.
Mr. Shand has placed his finger on perhaps the most embarrassing deficiencies in our store of basic data and has emphasized the economic importance to the country of the services which rely for efficient planning upon the adequacy of these data. His renewed appeal for extension of the rain-gauging and stream-gauging networks should be taken up and echoed by all hydraulic engineers. Those who have endeavoured to relate the measured run-off from small mountainous catchments cannot fail to have noticed the paucity of actual measurements upon which the published isohyetal maps have been based.
Some additional South African examples of successful artificial recharge may be of interest to supplement Dr. Enslin's able review. The only large-scale operations known to the writer have been undertaken at Zebediela Estate near Potgietersrus. On a visit in 1955 it was seen that all three methods were used:- (i) Floodwater was diverted from the Mogoto Dam back into the river to ensure streambed infiltration. (ii) Stormwater and surplus impounded water were diverted or pumped into earth dams in the vlei area to recharge a 40 to 150 ft. thick layer of rubble overlying Bushveld basalt. (iii) Four boreholes were used in a Dolomite area.
The paper is of particular interest in semi-arid countries and the Author has shown the existence of a relationship between silt slopes inside the reservoir, river slopes and the ratio of length and average width of the reservoir. It may, however, be pertinent to draw attention to the fact that these phenomena are part of the whole. The part relates to a particular reservoir, the whole relates to the profile of the river as a whole. The phenomenon of silt deposition in reservoirs is undoubtedly a part of nature's reaction to a disturbance of balance.
The writer wishes to stress the fact, which is often overlooked, that all hydrologic investigations are inductive, and deductions can only be as reliable as the data on which they are based. So many factors affect hydrologic phenomena that it is essential that the engineer employed on the analysis thereof should have not only a sound knowledge of the basic hydrologic theories but also at least an elementary knowledge of meteorology. In fact, sound advice to the young engineer who is interested in hydrology is first accumulate a library.
In the papers that have been presented special emphasis has been laid on planning and housing in European areas and in the native urban areas. No particular mention has, however, been made of the position in the rural native areas. Delegates may not be aware of the fact that in the rural native areas, which are almost 18,000,000 morgen in extent, some three to four million natives at present have their homes. A large proportion of these natives make a living from the land. Others, however, make use of the native reserves to accommodate their families, but the major portion of their income comes from employment in European areas from which they return to the native reserves as often as circumstances permit.
The work that the Natal Town and Regional Planning Commission is doing in the Tugela Basin in particular, and in Natal in general, has always been admired by the writer. Mention should also be made of the excellent research now being carried out in the Eastern Cape by the Buffalo Catchment Association and Rhodes University, together with certain surveys prepared by the Natural Resources Development Council such as that for the Pretoria-Witwatersrand-Vereeniging region. These surveys may be termed regional surveys in the real sense of the word in that the facts, whether they are assembled from existing sources or supplemented by further research are co-ordinated and interpreted towards the specific objective of solving major problems concerning the development of the region concerned.
Over the past twenty years and more intensively during the past ten years we have seen the rise of six new towns associated with the expansion of the mining industry in the Orange Free State and the establishment of new steel and fuel industries on the borders of the O.F.S. and the Transvaal. In addition great developments have taken place along the line of the gold reefs known as the Far West Rand. Elsewhere all our older towns both great and small have been added to in no mean manner particularly in the sphere of housing for Africans.
Full cognizance should be taken of the increasing standard of living of the Urban Bantu in future planning with particular reference to the provision of freehold sites in native towns to be developed and built on by the higher income group of Bantu themselves. Home ownership is a basic human right for all races of population of a democratic country.
The Author has dealt very ably with a complex subject - the problem of future planning in terms of human needs and the advancement in science and technology to meet these needs. In an age when the advancement in technology is so rapid and startling, the task of the planner is to attempt to forecast long-term trends and to superimpose plans of extreme flexibility capable of quick adaptation to new and unforeseen changes. The problem in so far as human society is concerned is one of challenge and response. The task of the planner is to assist society to adjust itself to every new change in an orderly way and at the right time.
The Author's masterly survey of the significant trends in modern design procedures has come at a time when engineers are wondering whether they should seriously think of discarding their old, familiar design tools, whether it is worth the effort to acquire skill in the use of the new tools, what is the nature and order of the savings that may be effected and how well the new methods have been established by research and experience.