The Irrigation Question. 379 



direct evidence is not obtainable, to consult the oldest in- 

 habitant, but the information furnished by those worthies is 

 frequently very misleading and incorrect in recorded instances by 

 8 to 10 feet in the height reached by a flood. The designer naturally 

 does not wish tO' place his structure higher than necessar\- for safety 

 — to avoid unnecessar}- expenditure in piers, abutments, embankments, 

 and approach roads — ^yet, on the other hand, placing it a foot or two 

 too low may spell disaster, and much greater expenditure in the end. 



Equallv important is the knowledge of river flows in the case of 

 ^^•ater supplies for villages or towns or for industrial purposes. 



During the sittings of the Peninsula Commission the writer was 

 asked to furnish information with regard to the approximate cost of 

 surveys of the river sources of some of the principal streams within 

 50 or 60 miles of Cape Town. In not a single case were any data 

 available shewing the extent of the watersheds, the average rainfall, 

 or the amount of flow-off, all of which would have been found in the 

 records of a proper hydrographic survey. 



.Such a survey would also disclose the localities where permanent 

 weirs might be constructed tO' retain some of the water, which now 

 after heavy rains disappears into the sea in the course of a few hours, 

 thus robbing the agricultural lands of an inestimable benefit. 



^lany of the Colonial rivers, such as the Orange, the Great Fish, 

 the Oliphants, the Gamka, the Gouritz, and many others, carry with 

 their flood waters into the sea immense quantities of soil and organic 

 substances extremely valuable as fertilising agents. A series of low 

 weirs with sluices in each would hold up the greater bulk of such 

 matters, and when the floods have subsided the sluices could be 

 gradually opened, the water drained off, and the deposits allowed to 

 solidify, after which they could be carted away and deposited upon 

 the poorer lands and ploughed in. Or in places where the configura- 

 tion of the ground is suitable the silt laden flood waters could be led 

 upon such lands direct. 



Another useful feature of the hydrographic survey would be the 

 gradual collection of data regarding what has been done or is doing 

 at the present time in the various divisions of the Colony in the way 

 of irrigation. Of such ver\' little is to be found in official records, 

 and this mostly in connection with schemes carried out within the 

 last decade. It is well known, for instance, that irrigation is prac- 

 tised on a fairly large scale in the Oudtshoorn District, but what this 

 actually amounts to, what crops are raised, and in what quantities, 

 what area of land is actually under irrigation, the amount of water 

 consumed, the manner of its distribution, the sources from which it 

 is taken, are all matters which may be well known to a few local 

 people, but of which nothing reliable can be obtained from official 

 records. 



This paper has so far dealt with rain water stored directly after 

 it has fallen. There is, however, another supply available, namely, 

 the water which has been lost to ordinary storage by having per- 

 colated into the ground and formed natural storage reservoirs in 



