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save the Blue Tier

water catchment

- d. e. leaman, hydrologist

EFFECT OF LAND USE CHANGE ON WATER SUPPLY: Blue Tier Region, Northeast Tasmania

Introduction

The Blue Tier region has experienced several partial transformations since European settlement; including agricultural clearing, clearing and burning related to mining, some forestry, and wildfire. The latest change, now under way, involves comprehensive clearing and conversion of forest areas either to plantation or to forest regeneration and production. At no time in the past two hundred years has any agency sought to determine the effects of these changes on the quality and quantity of water derived from catchments on and around Blue Tier.

There have been water quality problems in the past; from mine tailings and erosion of slopes related to fires and other works. Quality variations must have contributed to historic changes to the Georges River system. Fortunately, these have been relatively short-lived and have occurred at times when competing demands and requirements for water were either of lower standard or much lesser volumes than required today.

The situation at Blue Tier, in so far as water supplies (quantity) are involved, is typical of much of modern Tasmania. There are many demands upon the limited amount of water available. That water has to be shared, equitably. Any industrial activity with a water demand equivalent to a reconstituted forest would be required to satisfy a raft of environmental and health guidelines before any licensing or approval to proceed was granted. Water demand would then be seen as a part of the commerce of the operation and costed in terms of inputs and effects on others. Likewise, waste water output and its quality, and management would be taken as a full part of a commercial operation. In this context we find that forest industry activities and proposals may be undertaken with no preliminary statement of demands or effects. This is an inconsistent and potentially disastrous legislative attitude. Consequently no impact statement or appraisal of effects on water supply exists for any region subjected to plantation conversion or forest clearing - including Blue Tier.

The Water Cycle and Legislation

Some basic information is needed by way of explanation since the controlling legislation fails to include any appreciation of all the factors involved, or even acknowledge some of them. This must mean that the creators of the legislation were unaware of the significance of such factors; something which must be remedied promptly.

Current legislation (Water Act and Policies) emphasize management of surface water and obvious catchments. Complete management of catchments, however, requires us to understand the subsurface element of each catchment and the materials which store, transfer or chemically modify the great bulk of the water in the catchment. This element is wholly ignored in most legislation. Water from the atmosphere or surface may pass underground and reappear as surface flow or vapour. Vegetation, including trees, may draw directly from the subsurface store and so alter the transfer volume returned to surface. The groundwater storage and transfer system supports environmental flows and carries stream systems though dry periods.

Our laws, including the regulatory documents such as the Forest Practices Code, fail to recognize these realities and, as a consequence, the issues of contamination, pollution control, recharge protection and sustenance of catchment yield are either misunderstood or ignored. Emphasis has historically been placed on the engineering elements of catchment flow to the detriment of comprehensive management for all the possible users of water in the catchment, including the environmental and ecological factors. This integration of quality and quantity issues, and surface and subsurface water factors is long overdue; no sensible state policy on water usage is possible without it. It is not in sight and there is no evidence that its need has yet been realized, as judged by the recent job specification for Principal Hydrologist with DIPWE. The ramifications and implications of this deficiency are far reaching.

Our Environmental Protection legislation has much to say about water contamination overall but little about the effects of surface activities upon subsurface waters and it totally fails to appreciate that contaminated groundwater eventually appears at surface somewhere, sometime. Surface water can thus fail to meet set standards, not as a result of nearby surface activities, but perhaps as a result of more distant surface and ground activities. Unless both types of sources are managed then the standards are worthless and impractical (see Leaman, 2003a). Clean rivers may thus depend on good industrial or good agricultural practice; and the latter is nowhere general while fertilizers, poisons, pesticides and similar compounds can be applied without any regard for the consequences upon groundwater and total water system quality These acts offer no protection of water quality whatsoever, such that the base flows required to sustain the local environment may be guaranteed.

The Water Acts and State Water Policy are likewise much concerned with management of surface flows, irrigation - itself a risky practice if the entire water system is not considered, dams and storages, and flood control without any appreciation of user effects and management. No management system can work which bases its allocations solely upon stream flows without due regard for other activities, such as crop, clearing or forest effects in the catchment. The demise of the previous Underground Water Acts, themselves strictly limited, has completely destroyed any sense of balance.

Acts dealing with Forestry, including the Forest Practices Act, focus upon the trees and generally ignore hydrological issues. They thus overlook the reality that trees require water to grow; water which has to come from somewhere; either catchment excess, or be taken from other users.

Forest practices which affect water are "consistent with the State Policy on Water Quality Management" (Forest Practices Code, 2000; section D2). Given that this is deficient (above) and exclusive of the effects of added chemicals (implicit in D2.1), quality considerations are weakly handled (below) and unsatisfactory. Section E2 dealing with use of chemicals quite omits the reality that chemicals can reach the water table, and subsequently pass to the surface water system. Do "forest owners" who permit and undertake such activities (E2) fulfill their "responsibility to protect people and water resources ..... ?" No.

Quantity issues are mentioned only in terms of the word "flow" as in section D2 but are nowhere discussed. Nor is it explained how flow will be protected. But then, the Code does not have to since the founding legislation provides no instruction or guidance on this topic. It follows that the Code cannot offer protections for factors it excludes. The general public is deluded if it believes that the Code protects their water supplies at any scale, whether local spring or city supply, and there is no obligation on the part of any employee of Forestry Tasmania or the Forest Practices Board to do so - which is why they can act in a cavalier fashion when dealing with water supplies and water problems. Appreciation of what a stream is and prescriptions about streams are inconsistently managed as a result of this absence (compare sections C4.3 and Table 8). It is simply assumed that by providing streamside reserves, flow and supply are protected. This is a nonsense since it ignores the ground storage.

Overall, Tasmanian legislation with any relevance to water or water usage is weak, incomplete and often inconsistent. Contrary to our laws there is only one water system, and it is fully integrated. Nature is not compartmentalized (Winter et al., 1998). Realistic change is needed.

Forest Water Research

The two elements of the water question (quality and quantity) are related (see Leaman, 2003a); an aspect only appreciated when the entire hydrological cycle - including groundwater - is properly integrated into the assessment process.

Current Research by Forestry Tasmania, begun at its Warra test site in 1999 (Ringrose et al., 2001), is dominated by quality considerations - mainly siltation/turbidity - and nowhere specifies any evaluation of quantity losses or gains due to forest operations. Indeed, the main Warra stream and catchment cannot supply this information since the project is not designed to test the proposition, nor is this portion of forest destined for transformation. As shown below, some information exists from overseas and interstate studies but no significant Tasmanian research has ever been completed or published on local forest hydrology and water demand. Only Leaman (2003a), for a test site near Eaglehawk Neck, has presented any seasonal data for demand and transpiration variations and their effect on stream yield. The quantity question has been ignored for decades.

Various overseas and interstate studies (e.g. Watson et al., 1998, Chang, 2002) have shown that forest clearing and forest replacement, whether by natural causes such as fire, or human activities such as clear felling and replanting, leads to significant changes in the water balances of the local catchment. These changes persist for decades. Leaman (2003a) attempted a comparison of the patterns of change but the most demanding conditions arise for land use transformations which are total or repetitive.

Any clearing of forest leads first to an obvious increase in catchment yield due to surface or overland run off changes. In this early period the groundwater recharge may be much reduced with the result that local streams may display more erratic flow character. The change in yield may be as much as 70%. depending on tree species (Chang, 2002), but typical values are of the order of 50% (Vertessy, 1999, Chang, 2002). The increase in yield is short-lived, however, since the forest regrows rapidly. Yield to streams then declines rapidly as the trees absorb water from storage. The groundwater and recharge aspects of the water cycle become critical at this stage The water demand of growing trees soon exceeds the water demand levels which prevailed in the preexisting forest or mature forest and the elevated demand persists for several decades at least and may be measurable for more than a century (Watson et al., 1998, Vertessy, 1999). Peak demand, which may exceed mature forest levels by about 50%, occurs about the time that the new forest achieves canopy coverage. As noted by Leaman (2003a) other water users in a catchment may notice the loss of water if the streams in that catchment are marginally gaining streams since these may be converted to losing or intermittent streams for some time. Normal yields are eventually restored (perhaps a century or more). The peak yield and peak demand periods of such a cycle, as might be most simply produced by a fire or a single regeneration process, are of different lengths and differ by an order of magnitude (e.g., 2 and 20 years). The precise effect of such land transformations depends on the terrain, climate, elevation, species, soils and proportion of catchment involved. It should also be noted that there is a considerable difference between forest regeneration after wild fire, or after clearing - perhaps with firing, and replanting. Wild fire leaves some trees, many stems, relatively undisturbed soil conditions and much opportunity for mixed species regrowth and sprouting. Forestry activities allow more erosion, generate much more disturbance, and recovery demands on water are higher per equivalent area due to total nature of the clearance.

Leaman (2003a) suggested a differential demand function for such conditions. This function suggested that the difference between normal or previous demand and the the changed demand across the life of the forest restoration. In the early phase the demand is reduced (greater run off) but then the demand rapidly increases and stays higher than previously until the forest matures. The precise nature of this demand differential function depends on local conditions and must be determined for individual cases It is not known for any Tasmanian location and yet we have forestry operations on a giant scale. This is irresponsible, and stupid, at best. This situation has been termed "flying blind with respect to yield" and "potentially catastrophic" (Finlayson, 2001).

Some rules of thumb may be suggested from available national and international research. About half the annual rainfall is required to sustain a mature forest but it must be recognized that plants will use the water actually available if in excess (see Pielou, 1998). The peak demand for an E. nitens plantation may be about 50% higher than old forest in the same situation with a peak demand at about twenty years. Stream declines may thus match this differential, or about one quarter of the total rainfall! (e.g. Vertessy, 1999; O'Shaugnessy, 2003; Leaman, 2003a). Leaman (2003a) also demonstrated the extremely seasonal nature of the demand and streams are easily driven dry when summer growth corresponds to summer reductions in rainfall.

Where forest plantings are destined for rotation, as in long term regeneration and plantations, then the hydrological situation is not so stable or simple although the same basic rules of thumb apply.

In an area under development for rotation forestry the patchwork quilt of plantations ensures a cumulative and ongoing effect. Each plantation, although but a small part of the catchment, undergoes the same differential demand cycle through its life as described above. The crucial difference between a one-off event such as wild fire and forest recovery, and sequential rotation forestry, is that the system is not completely altered and the differential demand function is less extreme. Plantations require rapid growth for their economics to work and this, coupled with the patchwork of clearing and replanting which is associated with such practices, ensures that demands per unit area remain near peak levels in perpetuity. There is no taper back to normal or original levels. This was illustrated in sketch models by Leaman (2003a) which suggested that the demand curve continues to rise until the end of the production cycle and then stabilizes at a high level after that time - provided the entire area which could be transformed has been transformed. If the process can be extended to more forest area then the demand curve continues to rise. These calculations were based on typical 25 year cycles but shorter cycles worsen the demand situation while longer cycles ease the situation provided that no more than 1% of the catchment is affected in any one year. The change in demand may exceed 20%. A similar process also occurs with longer term regeneration forestry (70-90 years) but the demand functions are much stabler and less overall.

The crucial issue for Tasmania is that these demand functions are not known for any area or any species or species mix.

Peel et al., (2002) used a method comparable to Leaman (2003a) to assess the impact of forest operations upon the catchment of the North Esk River. Various assumptions were made about the forest coverage and other conditions in order to construct a model of changing water demand over time. The estimates focused on low flows since these present the most critical conditions and directly reflect groundwater inputs. Their study concluded that the water run off reduction over the first cycle of rotations would be less than 5% but would exceed 33% in the second cycle based on twenty year cycles. These estimates are comparable to those inferred by Leaman (2003a) using different assumptions. Even CSIRO work for Forestry Tasmania is reported on the respective web sites (2003) as suggesting that reductions up to 10% are indicated. Such quotes do not state whether these are maximum estimates or simply the present level on an increasing demand curve of the type established by Peel et al. (2002) and Leaman (2003a).

All estimates quoted as percentages are inherently misleading: the actual quantities must be stated and this practice has been followed below for evaluation of Blue Tier (below).

In the absence of any detailed local research, the quoted values must be estimates but are considered conservative. Any water losses estimated must be increased by any further clearance and planting. The research and its implication is not in doubt; only the actual water volumes for specific local questions are a matter for discussion.

The quantities implied are significant proportions of catchment yield. Such deductions from a steam system, which are devoted to a commercial profit-making operation and industry without any consideration of payment, or of effect on others, are happening without any controls or impact statement. This is incredible and incredibly silly since the effects will be long lasting. That it could also be done without any supporting research or analysis reveals the pathetic nature of Tasmanian regulation and law.

Note that everyone may be affected eventually. The first to notice will be agricultural producers in lower catchments since forests cream the water from the upper catchments; then domestic and town supplies.

Matters of quality have been more reasonably handled but it should be recorded that it is possible to distinguish sources of disturbance and changes in water quality (see Grayson et al., 1993). Leaman (2003a) also pointed out that the chemical character of the water in a catchment is dependent on the groundwater storage and transmission and that this might be affected by forest activities.

The Forest Practices Code

The Forest Practices Code (2000) attempts prescriptions for the planning and operation of forest activities, many of which are routinely ignored (e.g. Finlayson, 2002). It is, however, almost totally deficient hydrologically. While several sections discuss protection of water quality, mainly the management of siltation and erosion from roads and coupes, chemicals or oil spills, and some other sections mention flow, there is no requirement for sustenance or maintenance of flow (quantity) of water. Most such sections deal with the distance of a supply intake from operations; hardly a crucial factor.

The Code of Practice fails in its basic duty to every community or region in which it is applied. It does this by omission and the loss is covered by no other Act or Regulation.

  1. The Code does not require any preliminary impact statement nor any evaluation of the catchment content, existing demands or water value prior to any forest activity.
  2. The Code provides no controls or prescriptions about how to plan or manage forests in order to sustain acceptable stream flows, nor how to adjust them according to catchment type, climates, aspects, groundwater conditions, or seasonal effects. Variables may also include nature of operations (thinning, selective logging, regeneration, no forestry areas) and proportion of catchment influenced.
  3. There is no provision for maintenance of environmentally essential base flows.
  4. The Code overlooks entirely the significance and relevance of the groundwater component of the catchment and its impact on base flows and sustainability. Only in respect of karst conditions is this factor mentioned. This is hardly the general or typical case and quite distinct from normal conditions.
  5. The Code does not consider quantity issues at any stream stage, including the critical low flows.
  6. The Code notes that no more than 5% of a town catchment may be logged per year but it offers nothing about smaller catchments or isolated users who may depend on local supplies. The 5% rule becomes worthless as logging proceeds over many years, or the area is repeatedly logged. A town may still lose its water supply. The code considers quality of town water but if the quantity is nil, quality becomes irrelevant.
  7. There is no provision in the Code which can guarantee a water share for any other user of the yield of the catchment - whether for farm, domestic, town or industrial purposes. It is implicitly assumed that only forest demands matter. No other allocation system could tolerate this type of presumption. See also Leaman (2003a).
  8. The Code makes no provision for the cumulative demand changes due to plantation cycling, nor provides rules for the mitigation of such effects.
  9. The Code does not consider the possible impact of forest practices on groundwater quality due to seepage and hence ultimately on surface water quality at some future time.
  10. Code fails to recognize the hydrological characteristics of riparian sediments along alluvial plains, or of fractured rocks elsewhere, in its arbitrary definitions of stream reserves. Leaman (2002) demonstrated the quite inadequate nature of existing width specifications in terms of protection from pollution from any source.
  11. The Code sets arbitrary definitions for class 1 to 4 streams but then contradicts itself in terms of swampy areas. There is simply no understanding of what constitutes a headwater for a stream which typically begins with a spring or marshy area and a subtle but integrated surface and subsurface process in which a slight depression is developed to shape the landform. To suggest that the feature must have an area of at least 50 ha before classification is a patent nonsense. A better definition would be based on the existence of free water at surface for at least some of the year, coupled with indicator plants (sedges, reeds, ferns). The marsh concept with a protective reserve would then make sense, as would class 4. The current definitions are unworkable and unnatural.
  12. The Code must also recognize, and police, the need for contour working and not slope furrowing which leads to steam development and erosion as pointed out by Finlayson (2001). Size of coupe or catchment is irrelevant if a problem can develop.
  13. The Code, incredibly, allows removal of trees within five m of any stream classification including swamps and class 4 providing the machine is about 10 m from the watercourse and the tree is lifted away. This is hardly physical protection of the stream. Why bother with any kind of reserve if this can be done?
  14. The Code, for all its platitudes about protection of catchments and water quality, accepts no legal liability for any abuse or any action - accidental, or intended by forest plan - which diminishes the commercial or domestic values and amenities of others due to its unallocated use of catchment water supplies. This could be considered as theft, currently legal theft.
  15. The Code does not consider the location of forest activities within the catchment. Most activities tend to be in the upper catchment, usually where rainfall is greatest, and so the effect on the hydrology of the catchment is greatest.

The present Code, however its many other working aspects may be regarded by the community, should be discarded and totally revised to include a sensible and protective water policy.

Forest activity, or cessation of that activity, should be determined on the basis of available water; water excess to all other existing or likely needs including catchment sharing and town dependency. The forest demand should not be presumed to be primary, above all others, whether by intent for commercial purposes, or by default as permitted by current law.

One can only wonder if the Senior Scientist for the Forest Practices Board is totally frustrated by the hydrological inadequacy of the Code and its supporting Acts, or is unaware of the role and significance of forest water balances. Change is needed urgently.

In Tasmania-wide terms the massive conversion of upper catchments, especially, to single age, rotational forestry must lead to significant reduction in water availability in lower catchments. It is probably, given the age and rate of such conversions, that the yield reductions are currently in the accelerating early phases and that the events will not be devastatingly apparent for a generation. The situation may not then be recoverable, and certainly not within a century of realization.

The changes in yield which may be inferred will affect agricultural production, may lead to considerable capital expenditure due to lobbying to create water schemes which would otherwise be unnecessary, and transform town supplies.

The Forest Practices Code does not, and was never intended to protect water supplies. Nor does it generate any awareness in the public, foresters, contractors, operators, or forest industry generally that they may be using (taking) the water supplies of others without any judicial or regulatory allocation process. Nor does the Code provide any hint to anyone else that they may lose their water supply as a result of forest activity since there is no transparent impact or regulatory process. This is an untenable and unreasonable situation. Leaman (2003a) suggested how relative value, and prioritization of demand and output, processes are required to allocate the water resources of any catchment. But this is only possible if relevant Water, Environment and Forest Acts seek to define the resource and its limitations in a realistic manner. This ideal is not in sight and the failure to act may lead to the desertification of Tasmania. Forest industries will be mainly to blame if this occurs; permitted, of course, by inept governments.

The Matter of Risk

Every project or proposal involves some risk. It may be financial or environmental, or both. As noted in this report, and commented by Finlayson (2001), Forestry Tasmania is flying blind in terms of water yield issues with potentially catastrophic consequences for Tasmania. All published research, anywhere, indicates that this is likely if broad scale plantation and forest activity continues. Indeed, the situation may already be more serious than we realize.

Leaman (2003a) presented the concept of Pascal's Wager. This is a principle whereby one does not place all one's eggs in the one basket, or on a single bet; but lays off side bets. This is really common sense and great wisdom. The current forest practices assumes, by default if actually overlooked or insane presumption if known, that there is no water problem. This is a daring bet to take. What if it is a bad bet? Can Tasmania afford to get this wrong? Are we betting that forests do not use the amount of water implied? What if they do? There are many combinations of these questions and crucially, we do not have the data; the industry has proceeded as though it did not know. Here is scope for great tragedy or, as Pascal would say, loss of salvation. We are only entitled to bet with confidence if we have experience of the odds and the issues.

If there is any possible risk which involves great loss, as implied above, then there is a responsibility on the part of responsible governments and authorities to act in a way which ensures that the hazard is minimized and that the full duty of care is exercised. This means that any actions taken are essentially reversible in the short term. In terms of forests and water supply this translates into moderate use of our catchments, or parts of catchments, and less demanding styles of forestry. It also means that we need to select those catchments which can bear intense activity if that is the course we wish to follow. Whatever route is taken, no action should be proposed without appropriate assessment of the consequences.

The forest industry has escaped this kind of risk-value review until now. It is not entitled to maintain any such privileged position in view of the ramifications. The risk of costly disaster is too great and history, from ancient Mesopotamia to the present day, is replete with examples of peoples who thought they could beat the water cycle.

Legal Ramifications

It has been noted that the Forest Practices Code and its supporting legislation fails to protect non forest users of water in a catchment and it is possible that some forest operations may be subject to litigation for civil damages. Forestry Tasmania and the Forest Practices Board act within the law in allowing the current activities but that law does not necessarily protect other parties from damage as a result of officially sanctioned actions. Consequently both agencies, or any licensed agent, company or landholder might be subject to litigation where approval and the subsequent action has caused loss to another party. Activities such as private forest developments might also be captured if they lead to loss of water supply to a neighbour.

Such legal action would be conditional upon demonstrating that the activity had caused loss of supply and that some costs had been incurred due to its loss.

The Tasmanian government and its agencies are currently secure from such action since neither they, nor any others, have collected the data which might indicate culpability. This document, likewise, is dependent upon non Tasmanian data. In such circumstances the Forest Practices Board and any industry party would claim that the interpretation offered were unrealistic and deny the scale of any losses suggested.

For this reason it is essential that any community group or business which is at risk should collect the essential data and have it analysed. No claimant should depend solely on any government agency. Independent data is essential, if only as control, check or proof. This recommendation is listed below. Such groups should not delay in commencing their observation regime and must realize that some time may be required before the forest demand can be defined, and then to establish a trend of demand change.

Because damage may be done, and the business responsible may become defunct, long before the effects are realized then individuals, managers and planners should be placed on notice and the issue of transfer of liability investigted. The Mining Act at least, for example, requires a protective deposit so that damage can be restored should the terms of the mining lease not be met, or the company involved becomes unprofitable or bankrupt. The Forestry Acts should not be different, although it must be admitted that - if the conclusions of this report are valid - the deposit might need to be very large indeed, which would require the entire economics, or operation of the forest industry to be reconsidered.

The appropriate insurance would normally be that legislation requires an advance assessment and that proper base line data be acquired some years before any action. The present advanced state of the forest land conversions means that this is no longer possible in many catchments but trends toward lowering of yield may still be identified.

In current situations, where forestry activities have been allowed free rein, the only restraint might be the public response from an education program dealing with water supply questions and revelation of the increasing threat to domestic and town supplies.

At Blue Tier

The current forest operations plan for the east face of Blue Tier suggests an almost compete clearance and replanting over a ten year period according to various regimes - including plantation, regeneration, softwoods, etc. The plan inspected was inconsistent in its indications of what is difficult to log, road or regenerate but it must be assumed that the means will be found to log virtually al of each marked coupe. This conclusion may be based on experience in other parts of northeast Tasmania. Such totality of clearance, as planned, amounts to more than 80% of the forested parts of the catchments of the Groom and Ransom Rivers. The working plan is a patchwork across the region which thus far amounts to 350 ha and a further 200 ha in each of the next two years.

In order to assess the possible hydrologic effect of these activities on Blue Tier only the Groom and Ransom River catchments are considered here. About two thirds of each catchment is affected by the ten year plan, after exclusion of farmland and reserves. The two catchments comprise about 40% of the George River system.

The present stable forests, which are themselves now a recovery forest after historic activities including fire, logging and mining, should not be considered to possess a past history comparable to what is proposed. First, there was considerable erosion and soil loss to the George River system and second, the old forest regime involving minor surface disturbance and more selective logging is quite different from modern clear felling, ploughing, fire and dense replanting. There was no doubt some change in the catchment yield during and subsequent to those activities but no records exist which might quantify them although the alluvial mining of the lower George River may have been forced into difficulties as a result. The modern catchment, however, has to supply increased agricultural and residential demand at levels not experienced in the past. Previous history is not relevant to this assessment. The community has been living with the current output of the Blue Tier catchments and we need to determine whether it still can if that output is modified by the planned forest activities.

The evapo-transpiration budget for these stable forests is likely to be of the order of 3 to 5 ML/ha/year based on Victorian experience (Watson et al., 1998; Vertessy, 1999; O'Shaugnessy, 2003) This is a conservative and minimum estimate based on the available literature and new work at Eaglehawk Neck. In wet areas the demand could be as high as 9 ML/ha/year. Much depends upon the actual rainfall since the trees could transpire up to half the input.

The water demand under plantation conditions, however, is likely to be at least 7.5 ML/ha/year and possibly as high as 13.5 ML/ha/year. The deference between changed states is the water loss to the streams and this of the order of 4.5 ML/ha/year. These values are based on hardwood and eucalypt research but may be substantially increased where softwoods are involved (Pielou, 1998; Chang, 2002). As discussed in another part of this report the demand is sustained across the catchment and over time where the operation continues as rotational plantation system but peak demands may not be reached until twenty years into the operation.

These estimates, in the absence of local data, provide annual values and do not consider the effects of seasonal changes in growth or rainfall patterns. Trees can transpire entire precipitation inputs during summer with the result that ground storages are not recharged and streams are not supplied (see Pielou, 1998; Leaman, 2003a).

This can be illustrated by some simple calculations.

Suppose the average rainfall in the two catchments is about 1000 mm. This amounts to an input of about 10 ML/ha/year and is typical of the region about Goulds Country.

Now, consider the two rivers.

Please use wide screen for viewing data tables

River Input (ML)   Demand
(ML)
Total
Demand
(ML)
Yield (ML)
    Forest Farm/
pasture
   
Ransom River          
CURRENT summer 13000 9500 2250 11750 1250
  winter 15000 3800 900 4700 10300
FUTURE summer 13000 19000 2250 21250 -8150
  winter 15000 5700 900 6600 8400
Groom River          
CURRENT summer 15500 11500 2500 14000 1500
  winter 17500 4600 1000 5600 11900
FUTURE summer 15500 23000 2500 25500 -10000
  winter 17500 6900 1000 7900 9600

In these calculations the rainfall for each six months is a virtual halving of annual rainfall and may not be justified. This division does, however, stress what happens to the rivers and the seasonal contrast could be greater. Such calculations, ideally, should be made on a monthly basis with allowances for rainfall variations across the catchments but there is no possibility of this without real data - including stream flow data. What is demonstrated, however, even under these most basic assumptions is that both rivers run comfortable profits as gaining streams at the present time but that changed forest conditions would drive both the Ransom and Groom Rivers dry for several months. The total output from these two significant tributaries of the George River would be virtually zero for a large part of the year. This conclusion is conservative and even a sizable reduction in demand estimates will not alter the conclusion. Inclusion of a proportion of pine plantations will, however, worsen them. No modest tinkering with the figures will change the conclusion.

If recent experience in the present changing climate has shown that streams in the area can run very low in a poor summer at the present time then it may be concluded that such streams have little reserve capacity and the calculation should perhaps be modified. Future states may be much worse than predicted. Systematic climate change is an additional factor which could work against the rivers.

It may be concluded that the Ransom and Groom Rivers will lose their environmental base flows with no water available in summer. The two catchments will slowly dry out. The proposed coupe load is too high according to the conservative assumptions applied here and the forest plan must be modified.

Quality considerations are linked to the supply in such stressed conditions. Applications of any chemicals absorbed in the catchments will be returned to surface waters along with raised salinity levels. Low flow water may well exceed health and environmental standards as a result.

This report provides a local assessment for the foothills of the eastern Blue Tier. There are wider ramifications.

The George River catchment, and in particular the sub catchments of the North and South George Rivers, has already been modified by forest operations - which continue. This system may already display early signs of yield change (loss) as a result but not yet at peak demand. Were the George River system to lose the contributions from the Ransom and Groom Rivers then the entire catchment may well become arid and desiccated.

At this point it is necessary to consider the risks involved, the duty of care and the matter of reversibility. Blue Tier, and its provision of water, samples the issues raised by the entire forest use and water supply question. It is a case where land use conversion may not yet have reached the point of irreversibility. That point may well be reached in the life of the current three year plan if clearing and replanting continues. The ten year plan will guarantee permanent change. If all goes to plan (forestry development) and the results are as predicted then the living of many others is hazarded. All the bets will have been placed one way, with no covering bet. Pascal says this is unwise.

Responsible action, and a duty of care, requires that no proposal is so extreme that a poor outcome is almost certain. Prior assessment might have provided constraints but no such requirement exists. Given the likely situation in the North and South George Rivers and the probable decline in yield from them, a responsible action now would be to leave the remaining catchments intact. The risk can be stated starkly: either allow some free catchments, say the Groom and Ransom Rivers, or find another water supply for the town of St. Helens - because the George River will not be able to provide it.

A final question can be put. How is it possible to risk water supplies to a major town in this way without objective inquiry and public debate?

Note that the only alternative supply option would require a dam on the George River to collect winter run off and the expense of a new storage and supply system. Who would pay for this? Indeed, why should anyone pay for it when slack law, inadequate regulation and bad forest practice caused the problem in the first instance? Some important ethical and commercial questions are involved here since current forest operations are profit driven and yet both the forest and water resource are public assets and should be held in common. Users should pay for use of the resource, especially when they profit from it and penalize others at the same time The entire economics of the forest industry may be called into question in this way since the George River system is simply one river amongst many which will ultimately be affected by modern forest practices and policies.

Note also that dams are mixed blessings hydrologically (see Pielou, 1998; Leaman, 2003a) and should be avoided wherever possible.

Based on previous experience it can be expected that government agencies, the Forest Practices Board and forest companies will suggest the material in this report is all in error and no conclusion is significant. Such irresponsibility is always breathtaking but the possible risks should be taken seriously.

In any event no one can neither confirm nor deny the inferences made since no relevant data representative of Tasmanian conditions exists, an inexcusable condition in itself, while data from elsewhere leave little room for manoeuvre and certainly indicate the present conclusions are reasonable.

Visitation of the catchments also revealed that the forest plans appeared to ignore the risks posed by the varied soils across the granite terrain. Some of these soils are organic veneers on bedrock, others display erosive and gradational character while still others are developed on pockets of deeply weathered granite. The variation partly reflect differences in the local region in the last ice age. Parts of the terrain were protected and old weathering survived, other parts were exposed and cleared. The result now in that condition is extremely variable and the recharge characteristics also varies, not to mention flow control and species types. Some of these material will be damaged by massive disturbance, others will be washed away. These problems will affect the entire operation and, indeed, any future recovery or forest or hydrology. The coupe layout does not reflect any of this.

Recommendations

This study suggests several classes of recommendations; those which pertain to general law and codes of practice, those which involve issues of public policy and concern, and those which relate specifically to the Blue Tier and St. Helens region.

The relevant Acts which underpin water policy and forest management are in urgent need of revision in order that matters of water supply and water quality are handled in a consistent and protective manner. A realistic Forest Practices Code might then be possible which provides for the range of water management issues which must be faced by any State.

At the present time only a few such issues are regulated whilst possibly the largest user (and waster) of water - forestry - reigns uncontrolled. This is not a fair situation and the relative value of productive output per megalitre of water needs to be objectively assessed before deciding whether forestry is the appropriate industry in a given catchment. Such catchments are likely to be those with high inputs, large catchments and few competitive users where even low flows can be maintained on a perennial basis. Examples of such rivers would, on existing general knowledge, be the Huon, Picton, Florentine, and Weld Rivers and possibly the Derwent although many of its tributaries, such as the Styx and Tyenna, could be suspect.

Each catchment, down to so-called class 3 streams, which includes mixed users, whether farms or isolated residences, should be appraised by water balance audit for at least three years before any land use changes which total more than 5% of the catchment for the entire plan or proposal for that catchment (and not a creeping few percent per year for many years). If the water budget is such that in poor input years, the stream loses more than 10% of its low flow state, or its environmental support, then that proposal cannot be permitted without an equivalent exchange of water rights as agreed with other, existing, users.

Such an audit system would apply to large subdivisions and farm clearing as well as forest activities, or mining. It might, in some cases, require the cancellation or termination of existing forest plans since many of these clearly exceed the limits suggested. It would also require all users to treat the water resource more efficiently and consider the true value of water.

These suggestions may well be modified and refined after some observation and research.

While the best and most capable agents to organize the water balance studies might be State or Local Government - given that local authorities do have some constraining powers, it is clear that in the short term this work must be done by concerned individuals or communities. Details of basic methodology able to produce acceptable indicative results are given in the special leaflet available from Leaman Geophysics (Leaman, 2003b) Adequate precision is feasible with very simple and low cost equipment. Each stream should be appraised but reality dictates that each class 1, and representation from other classes, is all that is likely to prove possible. No water balance audits should be extrapolated from other areas, species, aspects or usage mixes until a wide sampling and extensive research has been reported.

We might, in this way, achieve a sensible and systematic best value use of our water resources.

The recommendations for Blue Tier are simple.

The present ten year forest plan for the area should be shelved immediately. Its application risks a failure of water supply from the Ransom and Groom Rivers and hence the George River. The town of St. Helens can expect a dry future unless this is done. The two rivers provide the only means by which the lower part of the George River catchment can be sustained. The risks attached to the present plan are too great to proceed in the absence of any kind of review, independently appraised after some years of observation.

This action should be taken now while it is still possible to avoid permanent damage to the entire catchment and supply to St. Helens. Community monitoring of the catchments should begin immediately.

All companies and government organizations involved in water management and usage, and their principals, should be advised of the situation in detail so that any defense, on the basis of ignorance of the risks and issues, can be removed.

References

Chang, M., 2002. Forest Hydrology, CRC Press, Boca Raton

Finlayson, B., 2001. Statement on the effects of clearing native forest and replacing with plantation forestry at Mt. Arthur. In Upper Catchment Issues 1 (2). Journal Tas. Comm. Resource Auditors Inc., Beauty Point

Forest Practices Code, 2000. Forest Practices Board, Hobart. (This version has been quoted since it is the only version generally available to the public and currently on sale)

Grayson, R. B., Haydon, S. R., Jayasuriya, M. D. A. & Finlayson, B. L., 1993. Water quality in Mountain Ash forests - separating the impacts of roads from those of logging operations. J. Hydrology, 150, 459-480

Leaman, D.E., 2002. The Rock which makes Tasmania. Leaman Geophysics, Hobart.

Leaman, D. E., 2003a. Land use and maintenance of base flow. Proceedings of Conference "A thousand cuts: the issue of land clearance"; Tasmanian Conservation Trust, Hobart, May.

Leaman, D. E., 2003b. The assessment of rural water supplies. Guide leaflet for communities prepared and available from Leaman Geophysics, Hobart, June.

O'Shaugnessy, P., 2003. Impacts of plantation development on the stream flow of Olivers Creek, Lorinna. Consultant Report to Lorinna community.

Peel, M. C., Watson, F. G. R. & Vertessy, R. A., 2002. Modelling of low flows in the North Esk River using the Macaque Model. Report for Launceston City Council, CRC for Catchment Hydrology, Melbourne.

Pielou, E. C., 1998. Fresh Water, University Chicago Press, Chicago.

Ringrose, C., Meyer, S., Bren, L. J. & Nielsen, W. A., 2001. Hydrology of small catchments in the Warra LTER Site: objectives and preliminary analysis. Tasforests, 13, 31-44.

Vertessy, R. A., 1999. The impacts of forestry on steam flow - a review in J Croke & P. Lane (eds.), Forest management for water quality and quantity. Proc. 2nd Forest Erosion Workshop, May, CRC for Catchment Hydrology, Melbourne, Report 99/6.

Watson, F., Vertessy, R. A., McMahon, T. A., Rhodes, B. & Watson, I., 1998. Effect of forestry on the hydrology of the Maroondah experimental catchments, Victoria. CRC for Catchment Hydrology, Report 98/9

Winter, T. C., Harvey, J. W., Franke, O. L. & Alley, W. M., 1998. Groundwater and surface water - a single resource. U.S. Geological Survey Circular 1139

Report prepared by:
D. E. Leaman, Ph.D., Hydrologist
Leaman Geophysics, Hobart, Tasmania
16 July, 2003

 

[Republished with permission of the author and editors of Upper Catchment Issues, which first published this in Vol.2#1B, ISSN 1444-9560. A summary of this article is available, as is a summary of the rebuttal of FPB criticisms of the above article.]

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