REQUIRED FALL OF WATER FOR SLUICING.

Otago Witness, Issue 1630, 26 August 1871, Page 4

REQUIRED FALL OF WATER FOR SLUICING.

The question of sluicing is a most important one in connection with goldniining enterprise, although in this colony it has not received a tithe of the amount of attention which has been bestowed upon it in California and elsewhere. We find in a Victoria contemporary some very important information in regard to the requisite fall of water per mile for sluicing operations, from a correspondent who signs himself "An Old Sluicer." In answer to the question, "at what fall per mile water would run to give a sluice stream," he replies, "If in a race ten miles long, it nmst have a fall of six feet to the mile to be of any utility. In the summer months a race of that distance, if passing along a country of open porous soil, will require at least two sluice-heads at the head of the race— or point of diversion — to secure the supply of one sluice-head at the terniimis, the evaporation and absorption being so great as to swallow up fully the one-half during that distance. If the race is cut with a less fall than six feet to the mile, the water very likely would cease to flow before it readied the further end of the race. For all practical purposes the long experienced sluicers of this district — sluicers of fourteen years' standing - condemn a less fall than six feet to the mile. In races of great length it is indis-

pensably necessary that a sufficient supply of water should be diverted at the head of the race to give the supply required at the further end where the water is wauted. The person cutting the i ¥ ace will require to take into consideration the length of the race, the nature of the country to bo traversed by it, and the quantity of water reqtiired at the point of delivery ; and, to make all safe, a fall of not less than six feet to the mile to insm'e a fair and necessary velocity to the How of the water, so as to save waste by evaporation and absorption in the dry season." Another correspondent confirms this estimate. He says :—": — " The gradient of a watercourse for a sluice, &c, may be safely taken as follows : Let the difference of level be one in one thousand (1=1000.) This will ensure a strong flow. If possible, secure 1"5 per 1000. In one mile there are 5280 feet. Now, one foot incline per mile will cause a perceptible and measurable rate of flow. If the gradient is to be laid out with an instrument, let the sights be taken at short distances ; this will ensure safer work, for reasons that need not here be explained. As a general rule, allow a difference of level of from five to eight feet per mile — the more the better, if the surface will bear it,"