OUR PUBLIC SCHOOLS COLUMN

Otago Witness, Issue 3234, 8 March 1916, Page 77

OUR PUBLIC SCHOOLS COLUMN

(Conducted by Magisteb, to whom all com mimications must bo addressed.)

FOR SENIORS AND JUNIORS.

[Magister vill be glad to receive Nature Notes, marked papers containing educational articles, diagrams, details of experiments, etc, of scholastic Interest to teachers and pupils. Correspondents must use OXLY one side of the paper, and whether using a pen name or not, must send both name and addkess.]

HARVESTING AND STORING THE

RAIN CROP

This, with tho sub-title "Wastage versus Storage," is tho name of an artiole I saw the other day in a recent issue of the Los Angeles Times, and tho article is as striking a 3 tho heading. It seems that it is proposed to spend about £3,200,000 near Los Angeles in water storage and distribution, but one party wants "to collect and concentrato storm "waters into runaways, to bo dumped like a cataract on tho lands below." But law suits ' show that this eystcm will entail damages which may double tho cost of construction. The devastation in the Cromwell Gorge recently, and tho cloud-burst on a smaller scale at Coa! Creek, Roxburgh, within a few days of the same date make us interested in "rain crops," and how interesting a subject it will mako for a "School Chat," a form of teaching I am a strong advocate of, for I am strongly of opinion that children should grow up in the atmosphere of what is going to be their after career, or of what is influencing their furroundings. A point made use of is the -filling up of check dams by silt. As a table shows, silt can absorb water from 33-£ to 53 pelcent, of tho space tho silt occupies, and tin's added to ordinary storage and to tho planting of scrub and of trees regulates flow and puro water at almost all times. Tho extracts I give ought to interest Central Otago residents, 'whether teachers or pupils, or not.

In one of the paragraphs quoted an article on Magnum terraces in tho Country Gentleman for last September < is mentioned. Can anyone- oblige me with a, loan of the number? WILD WATERS OBSTRUCT. There have been enough failures of storm drains to carry wild waters laden with silt and sand. Works costing thousands of dollars have- filled up 'n a single storm and wrought devastation by overflowing on to new lands and making new channels. There are truo principles .in every scienco which, if violated, wi'l exact m. penalty. The clogging up of storm ditches is tho penalty for a violation of principles in the handling of storm water. Between Los Angeles and Pomona on tho foothill drive there are passed a seoro of theso runaways that are annually clogged up to the menace of all lands below them. -Clear water, without silt, can be calculated to an engineering nioety, but no engineer can build structures that can endure the erosion and clogging by sand. Let us state tho laws of nature in the following order: Silt is the problem. Erosion causes tho silt. Velocity causes the erosion, Steer; grade causes velocity^

VELOCITY IS TiTE CULI'IiXT. To absolutely cure the evil of flood waters we have but to make the waters come out of the mountains slowly, not wildly. At first glance one might think it difficult to prevent rainwater from rushing madly down tiie mountain side. The most > important -things in the world are ill.' to accomplish when once understood. Forestry is the.first step. Check dams are the quickest in producing results, but must b:.■ augmented with tree and brush planting. Check dams are so named because they check the velocity and correct the grade by substituting frequent vertical drops of the water. That is the primary use of the chock dam; other important services rendered by them arc set forth below. Assume we have a r;;vine or side canyon, with a fall of 300 ft from the crest of the ridge to the floor of the canyon. Unobstructed water conies tearing wildly down this ravine, full of sand and silt, which flows into the main canyon and is swirled out into the valleys to clog storm conduits. Now build in that ravine about 40 check dams averaging 7ft to each drop. Tiie total of the vertical drops is then 260 ft. leaving only 20ft of actual grade. Each time the water drops over a cheek darn it has to gather itself up and start all over again. It has lost its head ; lost its punch, and half of it has sunk into the mountains to eecp out slowly next summer to "make so fair this, land of dreams. The grade having been cheaply corrected in that ravine, we have no velocity, and we c<!n then restate the laws of nature in respect to this problem in exactly reverse of the form stated above;

Corrected grade removes velocity. Without velocity there is no erosion

Without,erosion there is no silt. Without silt there is no flood problem

No flood-control system can violate these principles without paying and repaying every season the penalty in property damage. The clay of fencing the silt and water from jour own land -on to someone down below "is passed. It is but a short road .to travel to correct our flood troubles by check damming all the ravines. It is the simplest and least expensive plan of all. The principle of fall or drops must be carried out in the construction of conduits wherever the grade is sufficient to do damage. This mean.? wider conduits, of course. The laws governing flood waters and the laws governing irrigation water are one and thp same. Any engineer who should build irrigation canals without providing drops to control the grade would soon be out of a job. " FILLED UP " WITH EBBOBS.

A leader of tho opposition to conscrva tion first is quoted as follows:

" There are no reservoir sites in the mountains of any size. The check darns may retard the velocity and peak of small floods, but large floods will ' fill them up' and run right over them." This is but an expression of the popular idea that water storage is . accomplished only by means of cement reservoirs and redwood tanks. The absorption power of the mountains above us is almost incomprehensible. Fill a bottle with fine road dust and you can still put in half a bottle of water. The mountains should be viewed from the standpoint that they are bottles filled with sand capable of enormous saturation capacity for water in the voids of earth particles and the rock crevices. An article on this subject by Professor Gilbert E. Bailey, of the University of Southern California, says: " The best place to .store water for use in time of drouth is in the soil itself, by converting the subsoil of every acre into its own reservoir." The same authority gives the water-hold-ing capacity as follows: Per cent, of pore space by volume. Clean sand contains ... 33.50 per cent. Medium sand contains ... 41.80 per cent. Fino sand contains ... 44.10 per cent. Silt loam contains 53.00 per cent. The common argument used against check dams is thus seen to be the second greatest value they possess. Check dams do "fill up" with silt and sand, and what is still more to the point, ,'t does not need mule' teams and Fresno scrapers to haul it there; and what is more to the point, they fdl up with the very sand that otherwise would clog and obstruct storm conduits in the valley ; and, still further to the point, the sand becomes a sponge to withhold water. Cheek dams pre guilty of the charge; they hoid back all the silt and a largo part of the water. With proper forestry work our mountains will hold ail of the dangerous part of the flood waters. This kind of water storage costs pennies as compared with, dollars expended in masonry storage dams. Now it is true that cement storm ditches " fill up" and then the water runs wild and makes a new check bed in the surrounding country. In this case we need mules and scraper teams to get it out. The " rilling up" is found to happen somewhere, and the conservationists plainly' show that the formation of these "sand sponges" which hold back tho flood water for summer use is better than to have "sand barricades" form in tho valley storm channels, where it lifts the torrential waters out of the old bed on to the rich level lands adjacent thereto. It is to bo hoped that this and the next generation will sec that every ravine on the face of our mountains is "filled up" with sand and silt. Looking out of your window to the mountains, wo urge that all of those dark-spot ravines you sea on the face thereof, which look to be only 40ft long, should be brush-fenced and barricaded so that, they fill up and stop further erosion and sliding. Every rainstorm trickles clown the bottom of each one of those ravines and constantly wears it deeper and deeper. Some of them will bo large canyons when your grandchildren arrive in .Southern California. You may think this a big job to restore the 'angle of repose" to the face of our mountains. Not at all. Do one at a time? Private land owners aro doing this work in a hundred directions since Tho Times Magazine brought these European successful tactics to public attention hero. Every man with rapidly sloping land should rend the article in the Country Gentleman, September 25 issue, on tho subject of'Magnum terraces. Without attention to these details tho fertility of your soil and tho land itself is being slowly washed away each year. BAINDBOP OUE VITAL CBOP. To conservo tho storm water is to conserve tho wealth of the community. Tho Biimo argument that could justify storm drains first would justify tho placing of a torch to our hay and grain fields and ''storm draining" those crops in smoko to the high heavens to avoid paying the cost of tho harvest. ENGLISH HISTORY. I think most of us aro now alive to tho necessity for teaching history in our schools,

and not in a pettifogging year by year or reign by reign manner, but lined in with broad, comprehensive strokes, .lust before Christmas l had a chat upon the subject with Professor Bedford, who take? both history and economics in the Otago University. The Professor is an enthusiast, and I know he would like to seo teachers attending his lectures, not be-causo he would bulge his pockets with fees, for the fee? go to the University, but because ho recognises that we must get hold of the teachers if the subject is to be intelligently taught and effiointly handled in cur schools. .