TRANSACTIONS OF THE SECTIONS. 217 



miles more of the embankment, thus showing " that with increased velocity there 

 must be abrasion." "Where floods even at higher velocities are not obstructed, no 

 such action takes place. The author in October ISG-j laid down a causeway of 

 " kunkur " metal across the Khadir of the Sutledge at Loodvanah level with the 

 surface of the country, and up to 1867 it was standing, and for anything he knows 

 to the contrary, it may be there still. Thus a number of floods huxc passed over 

 it at great velocities, yet as the water had its^j?'op«' had of silt there has been no 

 cutting. 



But to continue, the Eichna Doab being so little raised above the Khadirs, there 

 could be no great fall east or west ; consec^uently, with a plain fifty miles broad with 

 a considerable fiill towards the sea, the tendency would be for the floods to spread 

 themselves over it, and as the rainfall is so little, this drainage is ultimately ab- 

 sorbed. There is therefore no weari/if/ down of this plain by the action of water ; 

 so instead of there being any natural ridges, the surface of the country is so uniform 

 that the author found by one of his trial cross-sections, with points taken at every 

 400 feet, in a distance of six miles in a straight line, that the highest point did not 

 exceed in height the most depressed more than .3 feet, though the fall of the 

 country at right angles to this line was some 2 feet in the mile. It is this imi- 

 formity of the plain and the richness of the soil that make the Eichua Doab so pecu- 

 liarly well adapted for irrigation, and in this opinion the author is supported by the 

 late chief engineer of the Punjab, Lord Napier of Magdala. 



The courses of rivers in India are very changeable, so much so that Government 

 have to collect the land-rents in the neighbourhood of these rivers on a difl'ereut 

 system to other parts, so as to admit of change of proprietorship as the course of the 

 river shifts. These deep troughs or valleys, called '* khadirs," are the limits through 

 which the rivers change their com'ses from time to lime ; and though the course 

 may be said to he always serjjentine, the changes are not exactly so, but follow that 

 of the valley; thtis there is a gradual movement of all the bends downwards, so 

 that after a given luimber of years, say half a century, the river may be exactly as 

 it was fifty years before, but at the end of tweuty-flve years every bend would be 

 found at the opposite side of the valley. 



Sometimes the changes are more or less sudden, when instead of the channel 

 moving gradually down, these bends are diverted, and the two ends get silted up ; 

 thus these diverted channels often become a marsh, and are known by difierent 

 names in different countries, such as " broads " in Norfolk, " lagoons " in America, 

 "jheels" in Upper India, " dhars " in Bengal, and "choungs" in Burmah. One 

 remarkable feature of them is that they are on a lower level generally than the 

 main river, proving that the rivers are raising their beds ; but it is this peculiarity 

 that makes it all the more necessary to guard against the tendency of the main 

 stream returning to its deserted channels, and it is to this the author would more 



f)articularly call attention, for he believes that hereafter it may be a work of no 

 ittle dilHculty to prevent this where the large rivers are crossed by railways. 



During high floods a large body of inundation water passes down the vallev, 

 which is alt more or less under water, but its flow is retarded for various 

 reasons, chiefly owing to vegetation ; consequently, comparatively speaking, the 

 water is pure, and does not hold in suspension anything like the same proportion 

 of earthy matter that the main stream does. 



To give sufficient waterway by flood-openings to pass off all the inundation at 

 its natural velocity would require exceeding!}- large bridges. To increase the 

 velocity through the bridges implies a heading-up of the water with a still greater 

 reduction in the velocity on the up-stream side of the embankment, which neces- 

 sitates a still further reduction of the silt held in suspension. 



The water thus lightened of its load, rushes through the flood-openings and 

 reaches the down-stream side at an increased velocity, in nearly a pure state ; and 

 as it must take up a proportion of earthy matter due to this velocity, a violent 

 action takes place below the bridge. Nay, sometimes owing to this increased 

 velocity on the up-stream side, a scooping out takes place above the bridge; and if 

 the bridge happens to have a raised flooring, it simply becomes a submerged weir, 

 doing harm instead of good by deranging the flow. If floorings are to be used, 

 they should be as inverts to rest the bridge on, and not raised to a higher level 



