River Bank Preservation.

Clutha Leader, Volume I, Issue 11, 17 September 1874, Page 3

River Bank Preservation.

Ia thb Province hut. little seems to be known of the rise snd preservation, of the banks of riven by means of vegetation, except that which exists naturally. Let the mind revert to the early days of the colony, and what will it discover on the banks of theTaieribut flax, rapuand we-we. These after a winter flood were not earned away except in extraordinary cases, for example, when growing on a high clay or sandy bank. AU low river banks, while suffering under the disadvantage of constant submergence, are safe from barm in case of floods, if protected by natural vegetation, even if it be only grass, such as tussock and we-we. The reason is that the water currents waste their strength on the yielding surface presented by the grasses whose matted roots renders the surface of the ground impervious to the water action. Has any of our readers been along the banks of tbe Waitaki ? If so, then tbey will bave observed that tbe greatest wafer action is on the side where the least vegetation exists. This is perceptible in the deep curves and bends, where, on the opposite side tbe bank is covered with flax and strong grasses. Again on the same river tbe low banks are Jess worn that the more precipitous ones. The known rate current in this river averages eight miles an hour aU through ita course, and much more in floods. The upper part of its course is between high banks of a nature, which is liable to be washed away, and yet very little, comparatively is destroyed— owing to the natural protection it gets from vegetation. Look at any creek or river which flows through a wooded country; take for instance the Waiau, which is the western watershed of Otago. Along ita upper course this river has high banks which have been cut by its rapid tide through beds of gravel, leaving little or no room for the growth of vegetation ; yet we And scrub, flax, and grass springing up along its boundaries. It would seem, then, that vegetation will grow despite floods, aud is probably fostered by them in the deposit oi the very seeds which produce it. Let ns look at the New River near Invercargill. We find the banks of this stream wooded to the water's edge — the water action being very slow on the banks. Trees spring from the tender plant, up to vigorous youth, and in hoar age tbeir roots but cling tbe firmer to the soil. In places we see some patriarch bending his trunk in the tide, having succumed to its strength and wearing influences, but this is so gradual a process tbat the odds are against the water, unless more formidable powers are brought to bear on the banks protected by wood and other vegetation. Look at any of the small streams in the country, and compare them one with another. Take the Pomabaks, the Kakanui, the Waireka, the Waipahi, and examine their formations in relation to the arguments set forth, and anyone possessed of common reason will see the simplicity and strength of nature's bulwarks. Further, we will leave New .Zealand and take a few from the British North American •Colonies. Let us take a look then at the St. John River, which forms the western watershed Of New Brunswick, and part of the State of Maine. It is in many places over a mile wide. During the course of 100 miles it is a tidal river, and is fed by tributaries and. lakes. In its upper course it continues to exceed a mile in width, but is more rapid and difficult to navigate, on account of shoals, bars, and falls. This river freezes in winter, becoming a plain of lte. In spring the snow melts in the forests and back country, and the ice of the streams and river breaks up, assisted by the large quantities of water which finds its way thereto. Floods take place, to which •the swellings of the Molyneux, the Waiau, and the Waitaki are nothing. Inundations, which flood out villages aod towns, carry away barns with their living occupants, and farm houses floating down the stream — veritable modern arks — are no uncommon sight ; whole stacks of hay are plentiful on the river, while logs, roots, tree*, scrub, cakes of drift ice, and other debris go whirling down the tide. This is but a faint idea ofa spring freshet in this river, with a tide running ten miles an hour, two miles wide, and forty feet above the summer level. One would fancy there would emerge no banks at all after such a flood, but, thanks to the forethought and natural observation of the inhabitants of the country, the trees which natnre has provided as a protection against the water .action are left uncut. Tbe hazel bushes -which densely skirt the banks are not removed -to gain a few more ears of wheat ; :the wild shrub and thorny bramble is allowed to climb and spread over the roots of the elm, and the grasses to grow beside them. Dogwood, hardback, blue-joint grass, and joint rush foster one another and ■the soil, so that these banks rise from the ye low flood refreshed, and put on their summer suit earlier than those plants that -are not thus invigorated. The only banks which suffer are those which present an unclothed exterior* It is principally from these that trees are detached and* born away. Trees which have protected the river bank beyond the memory of the oldest inhabitants are plentiful, and bear on their bark and limbs testimony to the rough attacks of these floods. The grinding of huge masses of floating fee, working swiftly past them, sawing into their wood and carrying off their branches ; these are to which river hank timber is subjected. we have duly considered the subject before us, we can only return to nature after all, and say that vegetation „ the best known source of river bank protection. Spanish sanfoin, lucerne, French honeysuckle, clover (red and white) gorse, and Cape broom, all form good bank protectors. Gorse especially is fitted to produce a good covering, and on account of its density and tenacity of growth is copable of resisting even tfae flood force of •the Molyneux. <)nce conquer the water action on .the rides, and the matter of growing larger -vegetation is of easy .accomplishment. Nature is always ready to assist itself, and the prorogation of gorse -will be found to be simply following a natural law. Its success is therefore •certain. Tutu and flax is the natural •covering of our river banks. These are •Blow of growth compared with £orse, but have strong roots like it The elm, willow, blue gum, -swamp oak, poplar, and .evergreen?, auch as Scotch fir, larch, and spruce pine (black and white), are all good river bank trees. For high hank?, -the larch is best adapted ; for rocky ones, ihe firs and spruces ; while for low banks,

the poplar, elm, and oak are the best. Double shelter hedges of gorse on the .top of the bank would ensure the protection of the growing trees if set, as there is no use in expecting vegetation to occur without giving it an equivalent for natural shelter.