Section A.— ASTRONOMY, MATHEMATICS, PHYSICS, 

 METEOROLOGY, GEODESY, SURVEYING, ENGIN- 

 EERING, ARCHITECTURE AND IRRIGATION. 



President of the Section : — W. Ingham, M.I.C.E., 

 M.I.Mech.E. 



MONDAY, JULY 7. 



The President delivered the following address : 



THE VAAL RIVER AND ITS POSSIBILITIES. 



The Vaal River rises about 15 miles north of Ermelo, and 

 joins the Orange River at a point about 8 miles below Douglas 

 «ind 112 miles below Kimberley. The river is wholly within the 

 Transvaal until it reaches the junction of the Klip River 

 ^O.FS.), about 22 miles below Standerton, but from that point 

 the right bank is within the Transvaal and the left bank within 

 the Orange Free State until the river enters Cape Colony at a 

 point about 8 miles upstream of Fourteen Streams. The total 

 fall of the Vaal River from Beginderlyn Road Bridge, which is 

 about 80 miles above Standerton, to the junction with the Orange 

 River, is about 2,000 feet, while the bed- is from 60 to 100 feet 

 wide above Standerton, and increases gradually to about 800 

 feet at the junction below Douglas. The length of the river from 

 the Beginderlyn Road Bridge to its junction with the Orange 

 River is about 805 miles. 



The highest point of the catchment area is in the Drakens- 

 berg range, in the neighbourhood of Mont-aux-Sources, at an 

 elevation of about 11,000 feet above sea-level. 



The bed of the river is composed of a number of large 

 pools, with a series of falls between the pools. As the falls 

 usually occur where there is hard material or rock, engineers 

 always examine such places for dam sites. 



Some of the pools are several miles in length and 20 feet 

 deep, and the depth of the river to bank level ranges from 15 

 to 40 feet- The total area of the catchment up to its junc- 

 tion with the Orange River is 73,747 square miles, and the area 

 of the principal tributaries is given in Table " A." 



The flow of the river varies considerably, and apart from the 

 waterfalls, the velocity ranges from nil when the river is dry to 

 about 12 feet per second during floods in the neighbourhood 

 of Vereeniging, where careful observations have been made. The 

 maximum ilood discharge during the last 4c years at the site of 



