DRAINING THE SWAMP.

New Zealand Herald, Volume LXI, Issue 18678, 7 April 1924, Page 11

DRAINING THE SWAMP.

EASTERN HAtiEAKI. WAIHOU r IMPROVEMENTS. V' EXTENSIVE STOP- - BANKING.' NO OVERFLOW TO - PIAKO. - ~... l.;: , i.y.;;.., .. ..' . NO. VI.. , . The " Waihou-Ohinemuri River improvement scheme has an. important ; bearing upon .' the general problem of , the drainage of the Hauraki, Plain, but its immediate effects arc noticeable only on the eastern side of the vast " area through which the Waihou 'River, winds slowly to the sea. •,_, , , , A.. generation : ago , the Waihou - was .a much more free-flowing river than "it is ' to-day, although it always has been subject to tidal influence. The troubles which have made the present improvement works • a stern necessity, began when the first willow was planted on the bank. People, fired with a , commendable zeal for beautifying , the' river, planted willows iby the thousand; indeed, it is stated that one enthusiast offered, a reward of one shilling' for every , willow p&iuted. It would be an excellent thing if to-day settlers could ,bo persuaded to remove the trees ' for' one shilling each. The cost of removing some of > the veterans must be r. tremendous, for high-powered; haulers are often required, to say . nothing of dynamite. ■ v . ■ ■ A very beautiful waterway was created arid one can readily understand the' regrets of Mature-lovers when they survey the miles of trees ' that have 1 been ringbarked and killed to await; the hauling plant. This, however, has been vitally necessary to Jthe ;; scheme of river im-» ? movement and flood prevention. In actual act the willows were the . first cause of the deterioration' of the . river ;as a- waterway arid the chief ' draining channel •; for no less • than 280,000. acres.

Boots Caused Encroachment. ' The rcison was that the masses of fibrous roots, ever pushing farther and further . into the stream, formed a collecting base for silt, and encroachment proceeded ;at an amazing rate. There are /places where, *: -through the 'agency of willow,; roots, V the bank has encroached as, much ;as one chain. Near ; Nethertou a single willow caused an island formation of about one acre in extent. It can readily be ' understood, therefore, that bank encroachments along a stream that naturally, had ' too little fall to yillow of the quick discharge of flood " waters, caused _ serious problem to; arise, particularly in _ the upper reaches, where, at several " points, . an overflow had no escape, ' except through .depressions and .drains to the swamps of the upper Piako River on the west, a river already unable .to discharge adequately 'an . excess of. water or, indeed, meet normal demands. ; :'• T ; -;. .

The position in the Waihou and Ohino muri vatershed area became intensified by the silting up that followed ' the ' depositing of ; tailings v from the Waibi Goldmimng Company's batteries into the Ohinemuri. ■ This' fine > silt. is ■ carried down to the plain where it further - reduced the capacity of _ the ; river and iby several floods was carried ' over, pasture lands, causing a good deal' of temporary loss.'l'V- (((-t: In ■ 1910 a \ Royal Commission . sat to consider the matter and it recommended comprehensive flood ; protection ( " works which ' have' occupied • the attention of the Public Works Department - ever , since. The first few vears saw little ; work (that was obvious, the time being spent in the collection of data , and the formulation of a , scheme as far as < such ( a scheme can be (formulated -in' advance! ( Naturally in hydraulics of . this character where floods and tides complicate land » drainage, it is impossible' to work to a' set (plan. It is ; not one : problem, but '"a" progressive series of problems,^ the solution of which must ( always be governed (by ; the financial factor.,(., ■' ' •< > . Two ' Canals' Across * Beads. < y Apart v from the removal (f of£ willows along the banks of the lower portion of the river,: the chief operation .; during; the war period ' was. the cutting of the Ngararahi arid KoutU canals 'to eliminate bends in ( the" Waihou. T They '( were completed in 1918, , the river * thereby , being shortened by about one mile, and ; their effect has ( been highly^beneficial.. Flood waters are now discharged much more ; rapidly and large areas, formerly,! menaced every winter at least, are now iu comparative safety. (.';"'(.( (~■•(;;(' ; ' v But the . cutting •of these (canals i does not represent . the ? mpst ( extensive I job under, the scheme. . ! No less than, 50 1 miles of step banks up to 12ft. .in height are involved. The construction ,of banks to full height has- not been , carried forward systematically, p however, , the ( .recommendation i> ; of -the ff commission ;of ( 1920 that smaller banks (be - built ;to (provide : partial protection having been adopted. This partial protection has been• provided v from Turehi ;to -Netherton • along the Waihou M and to the - Paerba; district along, -the Ohinemuri. r With -the exception of three small • gaps, ; where, very high flood waters might escape -to - the Piako side, > the .- western bank is now secure. Last week's • flood emphasised the need for the eastern bank being raided as soon as possible. •• •• • • -v* ■: The " construction of stop-banks does not ' represent ', the full .( extent of * the work •in ' these s sections. Throughout the adjoining land, where ? necessary, an " extensive -series iof ;■ canals is ' being. • excavated arid the water'; they ; collect is discharged into the. river; at convenient points. .'; v , '-■■■.:! ( ' ( . Modem Machinery.; ; ?In common' with the drainage works of the Lands Department, the Waihou 1 scheme has 7 been 1 greatly expedited by : the employment ( during" the' last three ■ years of modern excavating machines of ' the - type, though • smalls .used f(■ successfully h in the : construction of (the - Panama • Canal; A - dipper drfedge ( has - been employed (in cutting the interception > canals, ; and in the river a suction dredge : has- been - used with splendid r results for f the : removal of silt. /" Although (the silt is in solution when drawn ■ from' the (river, ?it - nevertheless is used for the building of stop-banks. The discharge is made through a pipe with holes at ' frequent , intervals. ..The volume from each hole is : not considerable,, and the small rivulets controlled bv men with shovels quickly, drop the silt, and the -bank rises. , " -

- Th» pride of the job, .however, is the Huston -drag-line f dredg«« — British ma-1 chines embodying the American 1 principle. Thev are '; steam ; f driven, !•'; and represent all that is I solid arid: durable iin the - British engineering } industry. Weighing no less than; 90 tons,: they, travel •on caterpillars three feet wide, on : the : firm- land of the river bank. The arms give a roach of over 60ft., and thus it «is - possible to dump the;- spoil over 120 feet ,> from: the water. ■ One of these giants has shifted 1000 yds. of spoil in eight hours. , r _' ( A Huge Stop-bank, i'V It -is a; thrilling sight to watch these monsters at work. The operator, who has four hand levers i. and - two foot controls, sits, keeii-eved.r and' concentrated, -, and ; is so expert that the '■ bucket, ' which has a capacity lof one > yard and a-half, water measure, moves almost with the precision of -a hoe in the hand of a gardener. It wings • out to the bank, y takes a bite, and without las pause is swinging ; round to the i point of ; delivery;" the: end of F the bank l: that ;v is 15ft. high. /Responding v instantly • to>.> the •?: touch of the lever,. . controlling c the ; tilting rope, ;it ; drops ; its load- and at once' is swirfging; back for,', another. ;Such "power and efficiency hold one spell-bound. Two men on - the - bank indicate ' where each' load should be; dropped, and smooth r; the - top and grade the Sides, but their work is not heavy— ito the V precision fof the machine.•" It ; does ■ not' leave anything else to be done, .for- every now and "gain 'it bites out a* piece of ; turf and drops it on the; top of i the bank to provide , a suitable • seed-bed for the''"grass that ■ is .to: be sown. v 4 It is interesting /to'v note> that Rust-en drag-line ; dred ?C6' ; are to ;be employed* by, the contractors for the Tauranga railway.