From Victoria University website: http://nzetc.victoria.ac.nz/tm/scholarly/tei-CarARom-t1-back-d1-d15.html#name-007584-mention
Mr. James McKerrow, formerly District Surveyor of Otago, whose early explorations and, considering the state of the country in these days, astonishingly-correct observations did far more towards settling the country and developing its resources than those of any other man, makes the following pertinent remarks regarding the economics of these inland water systems: "The lakes are a very great feature in the natural history of the country, and perform a most important function in its economy. They act as regulating reservoirs to the mountain-torrents emerging from them, for over their broad surface the floods find room to spread their volume until there be time given for the accumulation to pass away in the steady flow of one river. The value of the lakes as a means of restraining such rivers as the Clutha within safe limits will more readily appear when it is considered that the Wakatipu alone covers 114 square miles, the Wanaka 75 square miles, and the Hawea 48 square miles—altogether 237 square miles of lake to regulate its volume. These lakes have also a rise and fall of several feet. From the data thus given it will be evident that but for the tempering influences of the lakes, the Clutha, in place of flowing along a well-defined channel, a perennial stream, would devastate the whole country."
After nearly thirty years' European experience, the soundness of this theory, put forward at a time when the interior was terra incognita, can be fully attested. With the exception of a few miles of low-lying country at its mouth the Clutha has never been known to overflow its banks. With a body of water like this well confined, the bed in some instances has been scooped out to a great depth, the banks alone in these cases giving a drop of from 50ft. to 60ft. The country through which it flows is widely diversified in its aspects, varying from alluvial flats of great extent to abrupt mountain-gorges, in which barely sufficient room exists for road-making. Through some of its rocky defiles the river runs with great velocity. The average current, however, does not exceed four knots. In appearance these defiles are, as a rule, wildly grand. They form so many necks or funnels in the body of the river, at which the channel gets so contracted that the current receives all the greater impetus. The rush is for the most part that of a smooth volume, without any sign of submerged rocks or boulders. It does not demand great powers of imagination to invest these defiles with a handful of satanic lore and describe them as the devil's mill-streams, although it must be confessed the hydraulics are not generally recognised branches in demonology. The scene overhead is equally wild and suggestive. The precipices are high, the gorges in that way getting completely walled in. These precipices exhibit rocks and boulders striking all manner of threatening attitudes, from the slight list forward to the distinctly dangerous-looking, overhanging ledge. Some of these mighty excrescences look like turrets, embattlements, and hill-forts, but they are all too great, too magnificent, to be associated with the warlike operations of man. If we are to do them substantial justice we must bring the imaginative powers again into requisition and people them with a race of giants, armed to the teeth with the artilleries of heaven. That is the only way oat of the difficulty, and even then we may congratulate ourselves upon having escaped lightly.