WAIKATO RIVER DRAINAGE.

New Zealand Herald, Volume XLIX, Issue 14895, 22 January 1912, Page 8

WAIKATO RIVER DRAINAGE.

SCHEME TO LOWES THE FLOW

RECLAMATION AND NAVIGATION.

An interesting report has been presented to the Waikato River Board by Mr. 0. W. Kennedy, which deals with lowering the surface level.of the Waikato River through tho Board's district. It is stated that a large portion of the river district is low" land, and incapable of being drained by •■ gravitation. j After - pointing out the necessity of removing .shoal,, beds of pumice sand that obstruct' the lower reaches, the report states that the river flow is approximately 500,000 cubio feet per minute, and' ''above th© tidal influence the average fall is Sin. to the" mile. The average bottom velocity in "the reach below Mercer is- 100 ft. per minute, while according to authorities 40ft per minute will flow along coarse sand and 60ft in gravel.

| The report goes on : " I am of opinion that if the works recommended hereafter are carried out, considerable improvement will take place, though it is impossible to state exactly to what.extent. I estimate the . present .ordinary level would be lowered at least 3ft at Kaitangata, 2ft at Mercer, and slightly more at Fungapunga. Tidal influence "would probably extend -to Che bluff"beß»w MorcerJ arid, : incidentally, the river would be much improved for navigation/ * la order to lower the" surface level of the mer the shoals must be removed, and a channel of fairly uniform depth and width maintained.. -' "It is'proposed to define the limits of the channel by training walls, properly 1 located, and constructed of such suitable material -as the district will^nroyider-l suggest stone -be given, a trial • in the vicinity of and*Jbejpw Pakau, and- willows above.' These walft should not be continuous, bulr overlapping, each inclining slightly towards the stream,.- leaving openings of from "to lst)ft~ (according to "the? extent" of river-bed . excluded) "to permit of tidal and flood waters rejoining the channel. Considerable subsidence is certain to occur along the* Stone walls, and for -two or three seasons they will require attention and renewal, the height at which they should be maintained being between half and high tide level. '"The""willow walla should riot' be higher than will just leave their tops uncovered during floods. v " ■ These walla- will induce scour and effect improvement, but it may be found advisable "to employ further means to hasten the channet formatietfand remove the blocks existing in the upper, reaches. This can be done by " dredging. The 'sand forming the shoals is capable of removal by, a eand pump, the excavated material being deposited -in -paddocks behind the retaining walls. Provision may haye to be. njade,; foy contingencies, .in .the shape of removing snags and other obstructions, while, although there has been no Indication of rock at reasonable depth in.:the~<haane|s,,. no have -been made. . """ •'■'■•'■■'■'■: .:..,.,-..-■....<.- .• .■ " Concerning erosion of the banks, it is inadvisable to plant treo willows on the top and close to the edge of the bank; it is of no benefit, and during heavy winds loosens the surrounding soil and assists erosion. When protection is required it should* be done by securing long ■ willow bolsters, .boxipd* with wire, along the bottom of the bank, and planting osier willows at the bottom between the bolster and the bank." ;,_.._' Mr. Kennedy's estimate of the works -proposed is, approximately, £49,250, including A three and * a'-half miles of stone training walls, £7500* additions to stone walla during three years, £2500; 20 miles of willow training " walls, £16,000; sand tumps, dredge, and other plant*. . £3500; launches, £1250; working expenses ' for four 'years, - £10,000; surveys' and contingencies, £8500. T '?-','.