The Work of the Soil Conservation and Rivers Control Council

Forest and Bird, Issue 148, 1 May 1963, Page 4

The Work of the Soil Conservation and Rivers Control Council

The Soil Conservation and Rivers Control Council became established on the enactment of the Soil Conservation and Rivers Control Act in 1941. This is an act'to make provision for the conservation of soil resources and for the prevention of damage by erosion, and to make better provision with respect to the protection' of property from damage by floods. Object of the Council The general objects for which the council is established are defined in the Act as: (a) The promotion of soil conservation. (b) The prevention and mitigation of soil erosion. (c) The prevention of damage by floods. (d) The utilisation of lands in such a manner as will tend towards the attainment of the objects aforesaid. The objects v of the Royal Forest and Bird Protection Society are to advocate and obtain efficient protection of our native forests and birds and the preservation of sanctuaries, and scenic and other reserves, in their native state, and to enlist the practical sympathy of both young and old in these objects. The objects of the two bodies naturally differ but they .have a great deal in common, and the activities of each help the other in attaining its objects. The efficient protection of our native forests and of the native birds that assist them to thrive, which are objects of the society, help the work of the Soil Conservation and Rivers Control Council because adequate protection forest is one of the means for preventing soil erosion. On the other hand, the work of the council to conserve the soil and to prevent damage to the land by floods aids the aims of the society by fostering the maintenance of a healthy vegetative cover, which provides the habitat of many of our birds. Further, apart from the direct effect of the council’s work in encouraging the preservation of our native forest in fulfilment of its . own objects, there is an important additional effect: all work to conserve soil and to prevent damage by floods helps the fuller use of the land for many necessary purposes

and so reduces the demand for the further clearing of native forest to provide more land for agricultural and pastoral purposes. The information given in the rest of this article will give members of the society a better understanding of the work of the Soil Conservation and Rivers Control Council and of how this is related to the work of the Royal Forest and Bird Protection Society. Historical Background The indigenous vegetation of New Zealand developed in the absence of grazing or browsing mammals, the only vertebrate inhabitants of the land before the coming of the Maoris being birds, some of giant size, and two species of bat. With the coming of the white man the country, in little more than a century, suffered a tremendous ecological upheaval. Europeans introduced sheep and cattle to graze the native grasslands and later deer and opossums into the forests. Where grasslands were depleted the introduced rabbits thrived. Exotic grasses better able to support grazing animals were introduced and large areas of forest were cleared and sown to grass. This caused geological repercussions in a land already unstable, and there was a noticeable readjustment of slopes, particularly in the softer Tertiary mudstone country. The development of highproducing pastures, the clearing of . native forests, and the draining of swamps led to the more rapid run-off of rainwater and stream channels became inadequate.

There have always been flooding and erosion and the two processes have produced New Zealand’s fertile plains. The economic development. of these plains, as in other parts of the world, has made it desirable to control these natural processes and slow down - the rate of change. Almost from the beginning of settlement, works were carried out to alleviate flooding and river erosion, and various bodies were set up to control water. Even before the turn of the century some far-sighted observers recognised the incidence of accelerated land erosion ; but it was not until the 19305, when world-wide interest in the subject was aroused by disastrous dust storms in the United States, that serious consideration was given to soil

erosion. This led to the passing in 1941 of the Soil Conservation and Rivers Control Act, which recognises that soil conservation and the control of water in its widest sense are interrelated problems. Organisation and Functions This Act not only established the Soil Conservation and Rivers Control Council but also provided for catchment boards to be set up as the local executive bodies to plan and carry out works. Among the subsequent amendments provision was made in 1959 for catchment commissions in areas where the problems did not justify a catchment board. Commissions are more under the direct control of 'the council and the difference between a board and a commission may perhaps be illustrated by saying that a catchment board has ‘‘dominion” status whereas a catchment commission is a “colonial” administration. Government members are appointed to both types of authority; but the other members of catchment boards are elected whereas those of catchment commissions / are appointed by the counties and boroughs in the area. The Soil Conservation and Rivers Control Council itself reports to the Minister of Works and is administered by his department, which also advises the council on engineering matters; the Department of Agriculture advises it on soil conservation. Tn addition to Works and Agriculture, the Department of Lands and Survey, the Forest Service, and Treasury are also represented on the council. The remaining members are appointed by the GovernorGeneral to represent catchment boards, county councils, borough councils, river boards and drainage boards, areas outside catchment districts, and agricultural and pastoral interests.

The statutory functions of the council arise from the objects of promoting soil conservation, mitigating damage by erosion or flooding, improving drainage, and controlling water so that land may be used to fuller advantage. The. council is charged with the coordination of Government departments to achieve its objects and is required to provide a hydrological service and publish information. No mention is made of preservation of wildlife and the council has no power to withhold assistance arbitrarily from those who wish to drain lagoons and other water-bird habitats. On the other hand, the council is always pleased to

see farmers and acclimatisation societies develop for the use of wildlife any incidental areas of water that may result from the schemes it subsidises. These may be abandoned river channels, borrow pits, or farm ponds. No financial aid is granted for this wildlife development.

Although individual works are necessary to deal with small urgent problems, catchment authorities are expected to promote comprehensive schemes to control long , lengths of rivers or, for soil conservation, to organise aim-conservation plans over groups of farms covering whole catchments. In this manner the various techniques can be made mutually supporting and results are achieved much more cheaply.. Schemes originate from a local demand for improved conditions. Proposals are prepared by the local body, discussed with the prospective ratepayers and submitted to the Soil - Conservation and Rivers Control Council for approval and the granting of a subsidy. The Act requires that the local share of the cost be assessed on the basis of benefit received and rates are graduated accordingly. An essential part of each proposal is an

economic report on the benefits that will result. In the case of river-control schemes, these consist of prevention of losses and of increases in production following the land improvement that better control of water makes possible. With soil-conservation works much of the benefit may be "off site”, that is, on other lands or river channels that will no longer suffer from the deposit of detritus carried down from above. Nevertheless, it is usual, after the initial development costs have been met, for a farm-conservation plan to result in considerably better returns to the farmer as well as ensuring that the land is managed in accordance with its capabilities to give a sustained yield. There is no such thing as absolute control of erosion and flooding. Rivers are “biotic” entities whose character is determined by the climate, geology, vegetation, and fauna of their catchments. They are for ever changing, and all that man can do is to guide that change into . directions favourable to his own ends. Engineering works are required in the lower and middle reaches to contain floods and to train the. river to. a stable alignment. Soilconservation techniques are necessary over the whole catchment to prevent the overwhelming of the river works by detritus as well as to prevent land deterioration. Soil conservation is primarily achieved by maintaining. and improving the vegetative cover. There is no end to such operations. Periods of high activity will be followed by longer periods of quiescence, when only works of a maintenance nature are needed; but geological change and economic progress will sooner or. later make further major work necessary. Hydrology Hydrology is the scientific study of the water of the earth. It was stated earlier that the council is required to provide a hydrological service. This is effected 'partly through the hydrological work of catchment authorities and partlv by the delegation of the main responsibility to the' Ministry of Works. The civil-engineering division of that -department has a hydrology section in its head office and a hydrological survey that operates in the field throughout New Zealand. The hydrological work of the Ministry of Works embraces the collection of data, the analysis of information, and the publication of results for the national hydrological records; it also involves coordinating the hydrological work of other

Government departments and of local authorities.

The purpose of modern hydrological work is to obtain information sufficient for a full understanding of the phenomena of the water of the earth and of the problems involved in the assessment and use of water resources and the protection of these resources. To achieve this purpose hydrological data are, in New Zealand, classified in five broad subdivisions: water resources, river-channel measurements, flood information, suspended sediment and measurements of erosion, and measurements of catchment condition. These last are designed to record the catchment characteristics that influence the run-off produced from a catchment. The economic significance of water science in New Zealand has been indicated in a recent article by drawing a parallel with experience gained in the United States. It has been estimated that, on the basis of the same per capita expenditure in New Zealand as in the United States, the annual expenditure here on works for the use or control of water may reach £50,000,000 within the next few years. The magnitude of this estimated expenditure leaves no room for doubting the value of adequate hydrological data for the proper planning of the work represented. Much of the work in the development of water resources primarily concerns other authorities, but the hydrological work done under the authority of the Soil Conservation and Rivers Control Council is of basic importance to all water management and use. Further, the council’s own special activities in soil conservation, erosion prevention, flood prevention, and drainage all depend very greatly for their success on a thorough knowledge of hydrology as well as of agricultural science and engineering.

In the council’s own field of responsibility special efforts are now being made to present and interpret hydrological data in ways that will help to develop better scientific methods for the control of erosion and flooding. This is being done by the formulation of standard hydrological procedures and codes of practice that will not only aid field investigations and the design of works'but also give a firm basis for the fundamental research work required,

for education in hydrology, and for staff training. In all the work of the council good scientific information is important in another way; to enable the coordination of a complex working effort. Men of several professionsagriculturists, foresters, and engineers especially — are concerned jointly in expert studies and the planning of remedial and preventive works. This complex activity demands a high degree of coordination and mutual understanding, which is only possible on the basis of good scientific information. Hydrology is one of the most important aspects of this scientific background to working cooperation. There is often genuine doubt as to which are the most important and urgent things to be done in fulfilment of the objects of the council— for example, it is wiser to concentrate expenditure on the upper catchments of rivers or whether downstream protective works should be accorded greater urgency. Such questions have attracted wide public interest. For the best decisions to be made it is essential that reliable scientific information should be available, as only then can problems be solved logically and efforts be properly coordinated. Further, because the land, user will always be deeply concerned with both the problems and the proposed remedial action, informative publicity is most desirable; such publicity, to be effective, must be both suitable for the purpose and accurate, that is, based on scientific fact. Again, hydrology is

important because hydrological information is perhaps the most fundamental part of the scientific knowledge required in this field of activity. It will be seen, therefore, that the Soil Conservation and Rivers Control Council has every reason for promoting hydrological work. The Royal Forest and Bird Protection Society is naturally particularly concerned with watershed protection and will therefore be interested in the published proceedings of a symposium on hydrology and land management held at Lincoln College last year. At this symposium current work and future proposals were discussed. During discussions on the effect of catchment condition on the size of floods it was pointed out that there were some popular 'misconceptions causing unnecessary misunderstanding.' The misunderstanding mostly arises because of a failure to distinguish between small catchments and large ones. Most people are. inclined to think that when catchment conditions deteriorate floods everywhere will automatically be greater in magnitude, his is not so, broadly because the changes in water-holding capacity which follow changes in catchment condition are, for most soils, small in proportion to the precipitation of the storms of long duration that give rise to floods in large catchments. On the other hand, the same changes are likely to cause a very significant difference in the run-off resulting from the short intense storms that affect small

areas most. Erosive effects follow a different pattern. If the surface condition of a catchment deteriorates badly, especially if the soil is of an erodible type, there will be a very great increase in the rate of erosion caused by any degree of run-off. Erosion depends mainly on the flood run-off of little catchments and, as explained above,. the flood run-off from a deteriorated small catchment will be increased, thus further increasing the rate of erosion. These two effects combined result in the greatly accelerated erosion which follows catchment deterioration and which, measured as suspended sediment in the river flow, may . well show a hundredfold increase. Soil Conservation New Zealand commenced her second century of European occupation with the new responsibility of conserving her , landher main food-producing resource—despite the challenge to its permanence by the ruinous soil erosion that had set in during the first century. Soil erosion in New Zealand is mainly a problem of the hill-country pastoral lands, especially where farming has forced grass to take over the protective functions of the former native forest, fern, and scrub. Some 70 per cent, of the areas of New Zealand occupied for agricultural use is pastoral land that is too steep to be ploughable. Much of this demands special conservation methods of farming because of . the serious pasture deterioration, soil erosion, and weed infestation that have beset it. ' The protective, stabilising, and watercontrolling combination of vigorous native vegetation, litter, and spongy soil has given way in many places to a shallow-rooted, less protective and, in fact, threadbare carpet of grass on compacted, less pervious, and often exhausted soils. The problem is how to restore an erosion-resistant and water-absorbent combination of soil and vegetation and at.the same time, to maintain and even to increase the production from our pastures.

To develop practical soil-conservation techniques as a solution to this problem the Soil Conservation and Rivers Control Council acquired soon after its establishment, eight typical deteriorated and eroded farms as soilconservation reserves. Being typical hill country, these farms provided little scope for applying directly the array of well known soil-conservation .practices developed in the United States for ploughable land. They did,

however, give ample opportunity to investigate various adaptations of the limited range of soil-conservation practices applicable to unploughable hill country and also modifications of normal farm-management methods. The experimental work was undertaken by soilconservation officers of the Department of Agriculture. Additional experimental work was done on private farms, where the treatment of gully, slip, sheet, stream, and wind erosion was taykled directly by assisting farmers to do the necessary work to specified standards.

This early work on experimental and demonstration farms, together with the soil conservation works undertaken by catchment boards, yielded the following information and conclusions:

Spelling, or retirement from grazing, especially during flowering and seeding, revived both native and sown pastures remarkably and generally produced a cover on eroded land that resisted erosion and controlled water much better.

Surface sowing of clovers, and even grasses under some circumstances, resulted in the establishment of surprisingly good pastures on deteriorated sown and native grasslands, particularly when grazing was strictly controlled.

Topdressing with phosphate and trace elements proved to be the biggest factor in promoting the introduction of clovers and the strengthening of' grasses on deteriorated hill-country soils.

Rotational grazing of cattle was more effective than sheep grazing in regenerating poor pastures, and cattle obviated the need to burn native pastures periodically. When burning and rabbits were eliminated the rapid recovery of native pastures under controlled cattle grazing was most promising.

The value of planted trees in healing unstable eroded land, particularly in gullies, was confirmed in all districts, as was the effectiveness of native cover regenerated by complete spelling in areas of higher rainfall.

Pasture furrows were valuable in conserving water and reducing the scour of soil.

Graded banks and broad-base terraces were strikingly effective in stopping the loss of soil from cultivated slopes by sheet and rill erosion and in greatly reducing uncontrolled run-off.

Wide, shallow, grassed waterways proved effective in harmlessly disposing of run-off that could not be retained on the land.

Dams capable of temporarily storing floodwaters and regulating their discharge through a pipe demonstrated their merits.

Gully-control works, such as debris dams, drops, and planting, proved effective; but it was. found that they generally had to be supported by radical

changes in the grazing management of the catchment and by such measures as topdressing, terracing, and the diversion of the water away from the gully.

It was found that all the other conservation: practices were of limited use until topdressing and oversowing not only increased the protective value of the pasture but also increased the carrying capacity of the land and so provided revenue for other improvements and supporting conservation practices. However, topdressing and seeding are difficult and expensive on hill country. The economical solution was sought in the aerial mechanisation of this work. Fifteen years ago the Soil Conservation and Rivers Control Council began to organise and finance trials of aerial topdressing and seeding. They were so successful that the agricultural aviation industry was soon well established and has since grown phenomenally. Other work also done by the industry now includes poisoning rabbits and other vermin, dropping fencing materials in difficult country, and weed spraying. These are all used to help soil conservation, and aerial spraying is also used to kill willows when this is required for river-control works.

All these practices for reducing soil erosion have been incorporated in the policy of the Soil Conservation and Rivers Control Council. Another important measure the council promotes is the prevention and control of fire in hill country.

The planning of comprehensive soil-conser-vation measures in any area begins with a soilconservation survey. This has the purpose of determining the best permanent use for each unit of land in relation to its own characteristics and the whole of the catchment in which it is situated, according to the limitations imposed on the land by the physical factors of slope, soil, erosion, and climate. Such a survey provides a scientific evaluation of the physical and farming factors that determine the best use of the land resources and the conservation treatment required in the interests of maximum permanent production and minimum soil erosion. These surveys are based on a system of land-capability classification with eight classes, four for land suitable for cultivation, three for land not suitable for cultivation but suitable for grazing or for forestry, ’ and the eighth class for extremely rough, arid, or swampy land, suitable for neither forestry nor grazing but perhaps suitable for wildlife, watershed protection, or recreation.

It is sometimes well worth while to undertake isolated soil-conservation works but it is preferred that, from the soil-conservation surveys, conservation farm plans should be formulated. The land-capability classes are recorded in practical detail on a map of the farm. The permanent future use of each unit of land is planned within the economy of the farm and appropriate conservation treatments are developed for each class of land in each new paddock. The plan is then discussed in detail with the farmer, and the implementing of the plan is staged over a period of years to suit his resources. According to the needs of the farm the plan finally adopted combines good farming and the special conservation practices required for the best permanent use of the land.

The goal of soil conservation is the application of conservation-farm plans on every farm in a catchment. Greater protection and control can be obtained from closely integrated schemes, and s> further, instances of flooding and gullying and other deterioration often affect several farms. Farmers can do only a limited amount of effective control individually, but collectively they can achieve balanced control and full use of the soil and water esources of entire catchments. Conservation farm plans on farming land, supplemented by conservation forestry and other conservation measures on the unfarmed portions of catch-

ments, provide a soil-conservation scheme, which, coordinated with river-control and drainage schemes in the lower parts of the catchment, achieves a complete catchmentcontrol scheme.

Drainage and River Control

As with soil-conservation measures so, in the case of river and drainage works, it is often necessary to undertake isolated remedial jobs because of the urgency of correcting unsatisfactory conditions or preventing progressive damage. However, the broad purposes of such works and the means of achieving the desired ends are best understood by considering major control schemes covering extensive lengths of river valleys and including works both on the river itself and for the drainage of adjacent land.

The objects of major river-control schemes are firstly to stabilise the channel and increase its hydraulic efficiency, secondly to reduce the spillage of floodwaters, and thirdly to provide . a better drainage outfall for land requiring it. The first object is achieved by training works to induce freshes and floods to do the necessary excavation, by bank protection, and by cut-offs. The second object is achieved to some extent by improved channel efficiency. In more elaborate schemes general stopbanking is required and, in some cases, part of the major floods may be diverted down floodways or ponded. Achievement of the third object depends usually on normal river levels being sufficiently low for gravity drainage of the adjacent country. When the land is capable of high development better water control is justified and drainage water may then be pumped during periods of high river flow. Before embarking on a large-scale scheme to attain these objects two other matters must be considered: one is the condition of the catchment and the soil-conservation measures required so that detritus will not overwhelm the river works downstream, and the other is the economic benefit that the scheme will confer.

The predominant use of training works is in the shingle reaches of a river for the purpose of producing a single-thread channel. In its shingle phase a river generally occupies a wide bed containing braided channels that are constantly changing, and the axis of the river is usually relatively straight. To produce a singlethread low-flow channel in such a river

requires the introduction of meandering, so that water depth, gradient, and the size of bed material are in balance. The works used to bring this about are the clearing of unwanted willows, the construction of groynes to direct the flow in the desired direction, and the blocking of undesirable channels. Works over long lengths of river need to be coordinated so that they are mutually supporting. They may then be of lighter construction than when only an isolated length of river is treated. When a single entrenched meandering channel has been achieved, much of the original wide bed can fie reclaimed, first by planting with willows to encourage the deposition of material carried by the river and . then, when the land has been built up to a satisfactory level, by clearing the willows and putting the land down in grass. Training and channel-stabilising works are also necessary in the silt phase of a river, to prevent the undesirable cutting-off of meanders and to develop bends of easy curvature. In -these circumstances heavy rock is used extensively for bank protection, but anchored trees may be adequate where the attack is not severe provided the water is not too deep. An appreciable reduction in the incidence of flooding is obtained through the development of a more effective channel by means of training works. Sometimes it is desirable: to bring the natural river banks to a uniform gradient by small stopbanks across depressions. Additional protection against flooding can be provided only by continuous stopbanks. When the gradient in the lower reaches is flat the natural channel may be incapable of development to contain, the design flood. Sometimes it.is possible to correct the gradient by cutting a shorter channel to the sea. Alternatively, the flood flow in excess of what can be Contained in the channel downstream may be diverted down a floodway or spilt into a natural ponding basin. In time, economic pressure may enforce the abandonment of this last method because the land in the ponding basin is usually highly fertile.

Natural flood plains usually fall away from the river; and there is a belt of wet land along the foot of the hills bordering the valley. The; .country also falls in the same direction as the river, and .drainage from the wet land can be picked up by channels running roughly parallel to the river and discharging into it further downstream. There are two methods

for preventing the blockage of drainage outfalls by stopbanks along the river. The smaller outfalls may -be discharged through the stopbanks by means of culverts fitted with flapgates. When streams are too large to be passed through a culvert the stopbanks . must be returned up the tributary to higher ground. During floods in the river the flapgates close and local water ponds behind the main stopbanks; when return stopbanks are used the water in the tributary rises to a level controlled by flood level in the main river. When land becomes highly developed better water control is necessary than can be provided by a gravity outfall alone and pumping stations must then be introduced. These should always incorporate a gravity outfall, which, by operating when the river is not in flood, reduces pumping to a minimum. The Work Accomplished The 21 years since the constitution of the Soil Conservation and Rivers Control Council have seen the establishment of 13 catchment boards and three catchment commissions, all operating under the general coordination of the council. Each of these administers a territory bounded by the watersheds between major river systems. During this period also the various Government departments concerned have greatly increased their activity in the fields of work that are. the special concern of the council. Including the Waikato catchment, which is administered by a separate authority

constituted by a special Act, more than threequarters of the area of New Zealand is now covered by catchment authorities with the particular responsibility of attending to soil conservation and river control. Works of many kinds have been constructed in all parts of the country, and greater improvements have already been achieved in the condition of river channels, in the effectiveness of drainage in flood protection, and in the maintenance of our invaluable soil resources. At the same time the work has enabled great increases to be made in our primary production. The works carried out under the jurisdiction of the Soil Conservation and Rivers Control Council and the catchment authorities have cost in all about £24,000,000. Of this amount, about £16,000,000 has been contributed by the Government and administered through the council. Two cover photos depict erosion and its results For the benefit of young readers especially a few explanations of words used in the above article are appended Ed. Sheet erosion: the washing away of the top soil in thin sheets over a large area. < Biotic: having reference to all the forms of life of a district, their environments, and their influence on one another. Ecology: the study of living things in relation to their environment. Run-off: water that flows off the surface. Training works: engineering devices that induce a river to act in a desired manner. Spillage: spilling over (low-lying land). Cut-off: a short channel across a bend in a river. Braided channels are intertwined like rhe strands in a plait of hair) see illus. on page 8. Meandering: winding, turning, as applied to a river channel. Flapgates: gates that swing open only when water is being discharged. Detritus: any loose material resulting from the disintegration of rock. ' . ' . \ ■ J