British Geological Survey

TECHNICAL REPORT WC/97/17 Overseas Geology Series

GYPSUM GEOHAZARDS: THEIR IMPACT ON DEVELOPMENT - PROJECT SUMMARY REPORT

A H Cooper and R Calow

This document is an output from a project funded by the UK Overseas Development Administration (ODA) for the benefit of developing countries. The views expressed are not necessarily those of the ODA

ODA classification : Subsector : Geoscience Theme : G3 - Improve geotechnical haaird avoidance strategies in national planning Project title : Gypsum geohazards and their impx t on development Project reference : RCA90

Bib1 wgruyhic rtfcrtwcc' : Cooper A H and Calow R 1997. Gypsum geohazards: their impact on development - project summary report BGS Technical Report WC/97/17

Keywords : Gypsum, geohazards, gypsum dissolution, hazard avoidance, subsidence, water supply, national planning, local planning, cost-benefit analysis

Frunt c o w illustrutwn : Schema tic cross-section through a typical gypsum karst area showing the development of caves in gypsum and breccia pipes with subsidence hollows caused by the collapse of the caves. Gypsum is black, caves are uncoloured, cave deposits are yellow, collapse breccia is pale orange, limestone is blue, mudstone is brown, sandstone is dark orange, surface deposits are grey

0 NERC 1997

Keyworth, Nottingham, British Geological Survey, 1997

EXECUTIVE SUMMARY

GYPSUM GEOHAZARDS: THEIR IMPACT ON DEVELOPMENT

Gypsum (CaS0,.2H20, the raw material for plaster) is a rock which dissolves so rapidly that, wherever it occurs, it has a detrimental effect on development, construction and water supply. The hazardous characteristics of the rock are underestimated in the developed world and ignored in the developing world. Its presence, and the associated cave systems within it cause natural catastrophic subsidence that affects many urban and peri-urban areas and their infrastructures throughout the world. Gypsum encountered in damsites, tunnels and canals has resulted in expensive failures and difficult site conditions. Groundwater contaminated with dissolved gypsum is common, and gypsum karst aquifers are very sensitive to pollution. These aquifers are also very sensitive to water table drawdown and the associated generation of an enhanced subsidence risk. There is a need for improved understanding and recognition of gypsum as a geohazard and to introduce geological information into the planning and development process in gypsiferous areas.

This report summarises a collaborative study undertaken in China and Lithuania looking at gypsum karst geohazard problems. It was carried out under the ODA/BGS Technology Development and Research Programme (Research Contract R6490) as part of British Government recognition and aid to developing countries. The aim of the project was to help with the avoidance of gypsum geohazards in national planning and to develop generic guidelines to deal with gypsum geohazards.

A framework for incorporating gypsum geohazards in National, Local and Site Specific Planning is presented with examples from China, Lithuania and the UK. The most cost-effective way of dealing with gypsum geohazards is to avoid them rather than try to engineer around them. For National Planning, geological hazard maps, incorporating gypsum as a geohazard, are the most practical starting point for planning. On a local basis, detailed maps and planning zonation, with local regulation of groundwater abstraction, can mitigate the impact of the problem. On a site- specific basis, special forms of construction, including strengthened and extended foundations, can help to allow development to proceed; these measures are expensive and avoidance of the worst areas is the best practical solution. Measures to control surface water runoff and the avoidance of soak-aways is another practical way of reducing the subsidence caused by this hazard.

The avoidance of gypsum geohazards has an economic benefit. A framework for undertaking a Cost Benefit Analysis (CBA) is presented with an example of how it might be implemented to assess the impact of hazard avoidance versus non-avoidance.

The project publications are listed in Appendix 1.

GYPSUM GEOHAZARDS: THEIR IMPACT ON DEVELOPMENT

Research Project Number R6490

1 . INTRODUCTION AND PROJECT OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 . GYPSUM GEOHAZARDS AND WHY IT IS IMPORTANT TO AVOID THEM . . . . . . 1

3 . PROJECT INVESTIGATIONS AND THE COLLABORATIVE FRAMEWORK . . . . . . 3

4 . PLANNING FOR GYPSUM GEOHAZARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1 Strategic or national planning for the avoidance of gypsum geohazards . . . . . . . 7 4.2 Local planning for the avoidance of gypsum geohazards . . . . . . . . . . . . . . . . . . . 7 4.3 Local planning for the protection of groundwater . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.4 Local planning to avoid subsidence caused by groundwater abstraction . . . . . . . 12 4.5 Site specific planning for the avoidance of gypsum geohazards . . . . . . . . . . . . . 12

5 . GYPSUM GEOHAZARDS: AN ECONOMIC PERSPECTIVE . . . . . . . . . . . . . . . . . . . 13 5.1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.2 Analytical approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.3 Estimating costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.4 Estimating benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.5 Estimating net benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.6 Synthesis and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6 . DEALING WITH GYPSUM GEOHAZARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.1 Buildings and construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.2 Development and construction of roads. bridges and railways . . . . . . . . . . . . . . 18

7 . RESEARCH TAKE UP AND POSSIBILITIES FOR FUTURE COLLABORATION . . 22

8 . ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

9 . KEY SELECTED REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Appendix 1 . Dissemination of information: project publications . . . . . . . . . . . . . . . . . . . . . 24

Appendix 2 . The collaborative framework for the project . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Collaboration with Lithuania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Collaboration with China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Reciprocal visits to the UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Collaboration with Spain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Collaboration with the Ukraine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Appendix 3 Dissemination of information: project meetings. seminars and lectures . . . . . . 28

GYPSUM GEOHAZARDS: THEIR IMPACT ON DEVELOPMENT

Research Project Number R6490

1. INTRODUCTION AND PROJECT OBJECTIVES

This report summarises research financed by, and undertaken for, the British Government, Overseas Development Administration under Technology and Development Research (TDR') project R6490 to investigate and report on the mitigation of "Gypsum geohazards: their impact on development". The project was part of theme G3 to "Improve geotechnical hazard avoidance strategies in national planning". The work lasted about ten months and was undertaken in the financial year 1996197.

The objectives of the project were to scope and improve the awareness of natural gypsum dissolution problems in China and Lithuania. These problems include dangerous subsidence, difficult engineering conditions and groundwater pollution. The aim of the project was also to develop generic gypsum geohazard mitigation guidelines for use by planning authorities worldwide and to present a cost-benefit framework for looking at such work.

This report outlines the problem of gypsum geohazards in Section 2 and the collaborative work to understand them in Section 3; fuller details of the collaborative work are given in Appendices 2 and 3. Planning for gypsum geohazards is addressed in Section 4 and a cost-benefit framework for hazard avoidance strategies is set out in Section 5. Aspects dealing with construction and development in hazardous gypsum areas are outlined in Section 6. The take-up of the project and opportunies for future collaboration are given in Section 7. Appendix 1 lists the publications produced by the project.

2. GYPSUM GEOHAZARDS AND WHY IT IS IMPORTANT TO AVOID THEM

Gypsum (CaS0,.2H20, the raw material for plaster) is widespread throughout the world, but it dissolves so rapidly that it poses a threat to any development that encounters it. More than one metre of gypsum per annum can be easily dissolved by moderate river action on natural exposures. Where this dissolution occurs underground at similar rates caves can develop, expand rapidly and suddenly collapse. By this mechanism holes, commonly up to 20m deep and 40m across, continue to appear suddenly in gypsiferous terranes throughout the world. For example, in the towns of Ripon (UK), Pasvales and Biriai (Lithuania) 45,000 people are currently affected by catastrophic subsidence caused by gypsum. In Ripon the cost of the subsidence damage is estimated to be around &1,000,000. Half of the city of Darlington (UK) is affected by less severe, gypsum-related, subsidence. In Spain, parts of the city of Zaragoza and the surrounding areas are affected; the town of Calatayud has suffered severe subsidence and the new town of Puilatos had to be abandoned and demolished. Around Paris in France, and around Stuttgart and towns peripheral to the Hartz Mountains in Germany, gypsum dissolution caves have caused problems for road and building construction. In China large subsidence features, caused by gypsum

The TDR programme is part of the UK provision of aid and technical assitance to developing and emerging countries.

1

dissolution, have occurred in the Taiyuan and Yangquan regions of Shanxi Coalfield and in the adjacent Hebei Coalfield. Wherever there is groundwater movement and gypsum together, dissolution and subsidence occur. Subsidence caused by gypsum dissolution is reported from many parts of Europe (Box 1) including the UK, Lithuania, France, Germany, Italy, Spain, Switzerland, Cyprus, Poland, Rumania, Lithuania, Turkey and Russia. Similar problems are also recorded in China, the USA and Canada. Gypsum occurs extensively in many many countries including Libya, Iran, Jordan, Egypt, Mexico, the Gulf States and Pakistan, and problems may be expected to occur in these places as well.

Gypsum dissolution makes dam construction hazardous; water leakage causes dissolution in the foundations leading to abandoned projects, costly and potentially ineffective grouting programmes, or even catastrophic failure. At least 24 dams have been affected by gypsum dissolution problems including 14 in the USA, 3 in China, and others in Switzerland, Argentina, Siberia, Venezuela, Guatemala and Peru.

Water supply is affected by gypsum dissolution problems. Abstraction from gypsum aquifers can yield excessively hard water, accelerate dissolution and cause aggravated subsidence. Where the abstracted water is of potable quality, precautions are required to prevent the pollution of gypsum and associated limestone aquifers. This is because gypsum aquifers can transmit pollutants as fast as rivers. Poor agricultural practices can also cause severe problems in gypsiferous terranes.

In all the places where gypsum occurs there are natural or induced geohazards associated with the rock, but awareness of them is low. Throughout the world, little has been written about gypsum geohazards and scant consideration has been given to them in the planning and development process.

3. PROJECT INVESTIGATIONS AND THE COLLABORATIVE FRAMEWORK

The initial desk studies highlighted many parts of the world with gypsum geohazards. Lithuania was chosen as a collaborator because of the work already done there on gypsum karst hydrogeology and the agricultural regulations in place there to protect karst groundwater. In addition, it was chosen because it is an emerging European country with similar gypsum-related problems to those in the UK (Box l), where gypsum karst geohazards have recently become a formal planning constraint in the main gypsum karst area around Ripon. China was chosen because it has the largest reserves of gypsum in the world (Box 2), a very high population and enormous growth, with the potential for a considerable take-up of hazard avoidance measures. In China, the problems of gypsum dissolution are only moderately known and not widely appreciated as a geological hazard (Boxes 3 and 4). The project was designed to study the variation in the underlying geological conditions for gypsum geohazards, to publicise their existence and to advise on how to deal with them.

Details of the key project activities, fieldwork and collaborators in Lithuania and China are given in Appendix 2 and the Acknowledgements. In addition to the collaborative process of the research, the opportunity was taken throughout the study to publicise the dangers of gypsum karst geohazards by lectures and meetings, these are listed in Appendix 3.

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Box 2. Areas of gypsum in China where gypsum geohazards may occur.

-.

500km - i U /

In all locations in China where gypsum occurs there are likely to be gypsum geohazards. These can include subsidence caused by natural dissolution, gypsum-polluted groundwater, subsidence caused by the abstraction of groundwater, and hazardous coal-mining conditions. In addition to these hazards, the siting of dams on gypsum is particularly dangerous; leakage and dissolution of gypsum can cause dams to fail catastrophically. By using maps such as this, but on a larger scale, it is possible to plan for the avoidance of gypsum geohazards on a national and regional basis.

The map shows the age and distribution of the main genetic types of gypsum in China. 1. Cambrian marine gypsum; 2. Ordovician marine gypsum; 3. Triassic marine gypsum; 4. Carboniferous marine gypsum; 5. Cretaceous lacustrine gypsum; 6. Tertiary lacustrine gypsum; 7. Late Tertiary-Quaternary lacustrine gypsum; 8. Thermal and metamorphic gypsum (typical localities); 9.Secondary deposits of gypsum produced by karstification (typical localities); 10. Coal mining areas affected by collapse columns caused by gypsum dissolution. Abbreviations for province names: An-Anhui, G-Gansu, Gg-Guangdong, Gi-Guangxi, Gu-Guizhou, H-Henan, Hb-Hebei, Hn-Hunan, Hu-Hubei, IM-Inner Mongolia, Ni-Ningxia, Qi-Qinghai, Sg- Shandong, Sh-Shanxi, Sx-Shaanxi, X-Xinjiang, Xi-Xizang (Tibet).

4

Box 3. Gypsum geohazards peripheral to the Shanxi Coalfield, China.

Ordovician carbonate & gypsum formations

Karst-affected coal mines 7 Major springs

Geothermal boreholes Active faults

In the Shanxi Coalfield, gypsum karst underlies the coal-bearing sequences and many coal mines are affected by collapse columns that emanate from the underlying gypsum. These collapse columns lead to difficult mining conditions and act as potentially dangerous pathways allowing water to enter the mine workings. The karstic coal mines are located towards the margins of the coalfield and it is in these areas that surface subsidence associated with this gypsum karst can also occur. The presence of sulphate-rich springs and boreholes may aggravate the amount of gypsum dissolution and result in subsidence. The Shanxi Coalfield is an example of an area that would benefit from the production of a geohazard map incorporating information about gypsum karst.

5

Box 4. Gypsum geohazards associated with dam construction near Puding, Guizhou Province, China.

metres ,

1 36

30

A B

I 3 5 7 9 11 13 15 17 19 21 23 25 27 28

1353 ,

- 1350

2 1348

1347

1346

1345 1 3 5 7 9 1 1 13 15 1' 19 71 23 25 27 79

~ _ _ .

6 0

50

$ 4 0

* =e 30

-

g 20 v)

10

0

mainly reservoir leakage

Water with

1 3 5 7 9 I I 13 15 17 le 71 73 25 27 29

0.y.

The Huoshipo dam and reservoir were constructed, without any site investigation, on gypsum and limestone. Soon after the reservoir was filled, the flow of water from "Sand Spring" increased followed by a collapse of the reservoir floor. When this happened the clastic material was washed out of the spring and the reservoir lost considerable amounts of water. The reservoir is still leaking, and the water emerging from the spring has considerably more gypsum in solution than that in the reservoir. The gypsum is being actively dissolved by the leakage and could ultimately cause further collapses or possibly threaten the stability of the dam. Geological hazard maps incorporating information about gypsum geohazards would warn about the problems of developing dams in such areas.

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4. PLANNING FOR GYPSUM GEOHAZARDS

4.1 Strategic or national planning for the avoidance of gypsum geohazards

Strategic or national planning to avoid gypsum geohazards requires a recognition by geologists and engineering geologists that these geohazards constitute a problem that it is necessary and cost-effective to avoid. This summary paper goes some way to highlighting the problem and will hopefully be acted upon. Once the problem is appreciated, the best way forward for national planning is by the compilation of maps showing the distribution of gypsum and gypsiferous sequences. Commonly, these have already been compiled at a large scale for the assessment of mineral resources, or the interpretation of karst geology, thus very basic maps exist for countries like Great Britain and China (Box 2). A logical step forward from this initial mapping is the incorporation of gypsum data in general geological hazard maps or engineering geology maps. Depending on the scale of presentation, such maps could also indicate the susceptibility of the gypsum sequences to dissolution, a function largely controlled by the local hydrogeology, the thickness of the gypsum and the presence or absence of aquifers associated with the gypsum. The use of maps such as these may allow the worst areas to be avoided, or at least considered in more detail. Detailed maps showing the presence of gypsum for planning railway construction have been used in Turkey.

Items of national planning that can benefit most from taking gypsum problems into account include dams and reservoirs, any major construction such as roads, railways and canals, and the siting of new towns. A framework for assessing the economic benefits of geohazard mapping, based on comparison of alternative land use decisions, is presented in Section 6.

4.2 Local planning for the avoidance of gypsum geohazards

Local planning for gypsum subsidence can be of great benefit to the local population and avoid costly and potentially harmful development. However, the seriousness with which the situation is approached is also dependent on the local will to comply, the pressure on land use and the finances available for developing alternative sites or for constructing in problematical ones. There is a local balance between the risk that the population will tolerate and the amount both the public authorities and developers can afford to pay to avoid the problems. Thus solutions suitable for Great Britain may be completely unsuitable for other countries. In all situations, there is a clear need to identify and compare the full costs associated with alternative planning scenarios. In most circumstances, it is anticipated that hazard avoidance will be the most cost effective alternative.

Where there are long-established communities on gypsum subsidence-prone terrane the most practical approach is to try to limit the impact of the hazard. Failure to do this can result in developed areas becoming blighted with falling property prices and an unwillingness to invest in those areas. In England, Thomson and others (1996) reviewed the problems of gypsum dissolution subsidence and how it affects the town of Ripon. They approached the matter on two fronts, construction and planning. From their work, the local authorities now have guidance for development whereby the main thrust of avoiding the problem is through the planning regulatory process. They divided the Ripon area into three development control zones: A, B and C (Box 5).

7

Box 5. Local planning for gypsum geohazards at Ripon, North Yorkshire, UK.

73 4

72

B

71

A,B,C denote the Ripon development zones with their margins shown as pecked lines. Subsidence hollows are coloured black. Existing urban areas are shown with a horizontal or n amen t .

Like many towns built on gypsum, Ripon suffers from natural catastrophic subsidence caused by gypsum dissolution. The subsidence is ongoing and causes difficulty with planning. The areas of the individual subsidence hollows are of very high risk of further subsidence. The areas between and adjacent to individual hollows are of high risk of subsidence. The Ripon district has been zoned for planning purposes. The area of Zone A is outside of the subsidence belt and no gypsum is known to be present. Zone B has gypsum present at depth, but is largely outside of the subsidence area. Zone C has gypsum susceptible to dissolution present. Zone C is subject to stringent planning controls to enable development to proceed. These include the requirement that a detailed geotechnical report prepared by an officially recognised "competent person" is produced. Only when it can be shown that the risk of subsidence has been considered, and that the site investigation and structural design have taken this into account, will the development get planning permission and be allowed to proceed (Cooper, 1986, 1995; Thomson and others 1996).

8

Within Zone A there is no gypsum and no special planning constraints would be imposed. In Zone B, where the risk of subsidence is small, a ground stability report prepared by a competent person would usually be required and the problem should be considered in local planning. The Zone C area, with gypsum subsidence problems, would be potentially subject to significant constraints on development, and local planning should take these into account. Also within this zone, development is subject to controls. A ground stability report prepared by a competent professional person would normally be required before planning applications for new buildings, or change of use of buildings, are determined. In most cases this report would need to be based on a geotechnical desk study and a site appraisal, followed by a programme of ground investigation designed to provide information needed for detailed foundation design (unless this information, such as from boreholes, exists from a previous study). Where planning consent is given, it may be conditional on the implementation of approved foundation or other mitigation measures, designed to minimise the impact of any future subsidence activity. One key to the implementation of this approach is the use of a proforma checklist to be completed and signed by a competent professional person. For Great Britain, a competent person is defined in the report as a Geotechnical Specialist who is ''A Chartered Engineer or Chartered Geologist, with a postgraduate qualification in geotechnical engineering or engineering geology, equivalent at least to an MSc, and with three years of post-Charter practice in geotechnics; a Chartered Engineer or Chartered Geologist with five years of post-Charter practice in geotechnics". In addition to these qualifications, it is also desirable that the practitioner has experience of the problems though this is not formally stated. This procedure has been adopted by the local council, but is likely to be subject to minor changes with experience of its use.

On a local basis it would be possible to refine further the planning process by the use of detailed subsidence and engineering geology/geohazard maps. This would enable the avoidance of subsidence hollows and actively subsiding areas as part of the planning process, rather than as part of the investigation and regulatory process. However, this approach may put more responsibility on the local authority, whereas the regulatory process puts the responsibility on the developer to show that the site is suitable.

4.3 Local planning for the protection of groundwater

In Lithuania, groundwater in the gypsum karst areas is such a valuable resource that it is protected from pollution. The measures introduced here form a workable model for planning to avoid pollution in other gypsum karst areas. Firstly, the susceptibility of the gypsum karst to pollution was analysed by looking at 19 geological, hydrogeological and hydrological variables, then each area was given a susceptibility grading. The grade marking allowed the land to be divided into classes with varying susceptibilities to pollution and requirements for protection. The most important controlling factor was found to be the concentration of sinkholes or subsidence hollows which allow rapid runoff into the gypsum karst. As a consequence of this work, the land has been divided into areas for protection by agricultural regulation (PaukStys, 1996). By government decree, 27,600 hectares (276 sq km) of intensive karst are delineated with strict agricultural limitations, and 166,000 hectares (1,660 sq km) are defined as a karst protection zone. Four divisions of agricultural land use have been defined based mainly on the number of sinkholes per square kilometre. The categories and restrictions imposed are shown in Box 6.

9

Box 6. Planning for groundwater protection in the gypsum karst area of Lithuania.

LITHUANIA

Kaliningrad tus

n LATVIA

LITHUANIA

// .............. 'j;;;x;{"l ............... ................. / .................. <;;I ......................... j I; 1 i z; ;y .................... \ ............ I . . J

......... 1 ........... V A ! r ............ I \ ........... ........... \;j ' \ ,1okm,

1 2 3 4 5 p74 1-1 1-1 X ....... . . . . . . . . . . .

To protect the gypsum karst groundwater in Lithuania a classification based on the number of sinkholes per square kilometre (1 00 ha) has been introduced. Within the karst area the categories and restrictions imposed by law are:

1. Land Group 1 (up to 20 sinkholes/lOO ha). Grain crops should compose at least 50% of arable lands, perennial grass 40% and root crops (potatoes and sugar beet) not more than 10%. Fertilizers are limited to a maximum of 90 kg/ha of nitrogen/phosphorus/potassium (NPPt active ingredients) and 80 tka of manure. Triazinic herbicides and Chloroganic insecticides are prohibited.

2. Land Group 2 (20-50 sinkholes/lOO ha). Grain crops should compose 43% or arable lands and perennial grass 57%. Root crops (potatoes and sugar beet) are prohibited as is the setting up of new orchards and gardens. Fertilizers are limited to a maximum of 60 kgka of NPPt and 60 t/ha of manure.

3. Land Group 3 (50 - 80 sinkholes/100 ha). Perennial grass and pastures only are allowed. Fertilizers are limited to a maximum of 60kg/ha NPK. Mineral nitrogen fertilisers are prohibited as are pesticides (except for fungicides).

4. Land Group 4 (80 - 100 sinkholes/100 ha). Only grass meadows and forests are allowed. All fertilizers and pesticides are prohibited.

5. General karst protection area

Reference: PaukStys, 1996.

10

In addition to these measures, it is illegal to apply ammoniacal solutions to the soils of all four categories. It is also prohibited to use aircraft for spraying chemicals and mineral fertilizers. For the area around each sinkhole, in all four agricultural categories, the law is that there must be a 25m zone of exclusion to agriculture, and around some an earth barrier to prevent runoff entering the hole. Ecologically sound agricultural plans have been designed for each land group, and organic agriculture is being introduced to the region. Thus, the protection of karst water from pollution and the reduction of human impacts on vulnerable karst groundwater is official Lithuanian Government policy. The protection of the gypsum karst and its groundwater is monitored by the Government-funded Tatula Board, named after the local karst River Tatula. In addition, the Board supports training courses, gives loans to encourage environmentally-friendly (organic) agriculture and provides assistance with antipollution measures including the installation of effluent treatment plants.

In contrast to the protection of the karst water in Lithuania, some unsuitable practices have been noted in England. These include the piping of surface water run off from roads into sinkholes to drain it away (Box 7). In addition, during the 1970s, some large sinkholes in the Ripon area were filled with domestic refuse. Any leachate from this will have drained directly into the gypsum karst water system and may threaten local springs and wells supplying farms.

4.4 Local planning to avoid subsidence caused by groundwater abstraction

In many countries including Great Britain and Lithuania the abstraction of groundwater from the gypsiferous sequences, and those in hydrological continuity with them, has caused drawdown of the water table and local subsidence. The risk of subsidence can be reduced by the careful exploitation of the local water resources and the avoidance of this excessive drawdown, but in some areas this has an additional cost in the provision of an alternative supply. Similarly, the avoidance of water table drawdown associated with mining can be of benefit to the community, but the cost may be the lack of economic and social benefit related to the non-development of a valuable resource.

4.5 Site specific planning for the avoidance of gypsum geohazards

The development of individual sites on gypsum karst areas will be very variable dependent on the local geological conditions. However, some of the experience from places such as Ripon in Great Britain may be of use elsewhere. The first procedure adopted at Ripon is a desk study to compile all the previously known information about the site and the subsidence problem. The published 1: 10,000 scale geological map shows the distribution of the subsidence hollows, most of which must be regarded as potentially very unstable. In many instances, subsidence has occurred on several occasions in the same subsidence hollow. In addition to the hollows, the areas between them, or in line with other hollows, is also potentially at risk. This is because once a collapse has occurred, the cavity becomes choked and the dissolution can then continue in the immediately adjacent ground; in this way areas of amalgamated subsidence hollows can develop. The dates of collapse of the surrounding subsidence hollows and a knowledge of the local groundwater flow can also indicate the areas that are best avoided. Some areas will be deemed to be unsuitable for development; this is one of the costs of safe development.

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The desk study should also report on the preferred scheme for site investigation, and the parameters that need to be addressed. In many places including Ripon, Paris and Northern Spain, geophysics, including microgravity and resistivity tomography, have proved worthwhile tools for finding the most subsidence-affected parts of a site and for delineating hidden subsidence features such as cavities or filled breccia pipes with no surface expression. The geophysics survey can then be followed by a limited amount of drilling. In Ripon, Thomson and others (1996) recommended the use of cored boreholes, but as these are prohibitively expensive for most sites. Cost effective investigation can be made using chippings samples, but these must be examined by a competent geologist. One of the major problems in the gypsum karst areas is the misidentification of gypsum as limestone (even in cores), and the resulting reports may imply that in the absence of gypsum there will be no problems on the site. Once the nature of any underlying subsidence features have been defined, foundations appropriate to the planned construction can be designed.

5. GYPSUM GEOHAZARDS: AN ECONOMIC PERSPECTIVE

5.1 Introduction

One of the key contentions of this research project is that the presentation of updated information about gypsum geohazards by the production of hazard maps would improve land use decision- making. This informed decision making could limit or prevent significant costs, both financial and environmental, especially where large capital investment projects (eg dams) are concerned.

While such a conclusion would seem reasonable, few studies have tested the hypothesis in cost- benefit terms. There are good reasons for this: firstly, there are major methodological difficulties associated with the identification and measurement of benefits; secondly, few scientists have had to justify their work in economic terms. This situation is changing with the need to justify expenditure and show it is of benefit to the community.

This section of the report attempts to show how some of the principles of cost benefit analysis (CBA) might be applied to the avoidance of gypsum geohazards and the production of geological hazard maps. Firstly, we give an overview of some of the basic principals of CBA which underpin project evaluation (Section 5.2). This is followed in Sections 5.3 and 5.4 by a more detailed examination of costs and benefits, with particular emphasis on the nature and distribution of benefits. Section 5.5 illustrates how decision making involving water supply linked to land subsidence effects could be approached.

5.2 Analytical approach

Cost-benefit analysis is used as a decision-making method in project appraisal. In essence, it is a very simple method for comparing, over time, the predicted costs and benefits (either direct benefits, or costs saved) of a line of action, such as the adoption of a particular policy or project. To assess the worth of a course of action, two scenarios are compared: one 'with' the project, and one 'without'. The 'without' scenario is used as a baseline, or benchmark, against which the effects of a project or policy are measured. The present value of cost and benefit streams is then determined by a process known as discounting, in which future amounts are multiplied by a

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discount facto? to calculate the value today of amounts received or paid out in the future. Benefit cost ratios can then be calculated or, more typically, the net present value (NPV) of an investment is determined by discounting the incremental net benefit (the difference between costs and benefits). Decisions can then be made on the basis of whether a positive or negative value is obtained.

In the present case, we can view the 'with' and 'without' project scenarios in terms of land use decision making with respect to gypsum geohazards. Thus, the 'without' project scenario relates to land use decisions made without the benefit of new or improved geohazard information. These decisions - either hypothetical or real - can then be compared with those that might (or have) been made with the benefit of the information.

5.3 Estimating costs

The estimation of the cost of geological hazard mapping is relatively straightforward. Most of the work comprises desk studies and compilation, but costs are also associated with field checking and any remapping of areas with poor quality maps. In these instances, the hazard map production makes use of the existing geological information base, the costs of which will have already been underwritten by earlier funding initiatives. In other areas where geological maps do not exist, extra costs are associated with the need for primary mapping. In both cases, however, the broad cost sources are similar and include:

data collection in the field; data compilation and interpretation; data presentation, including digitising maps and database development; printing and publication; and distribution.

The production of a geological hazard map may mean that most costs are incurred at the beginning of a project, but it is important to note that maintenance of databases, map production and distribution will result in other costs being spread out over the lifetime of a project. Thus in areas where remapping and map compilation forms the basis of the 'with' project scenario, it is important to remember that maintenance of old maps and databases in the 'without' project scenario also incurs costs.

5.4 Estimating benefits

Capturing and valuing the full range of benefits accruing from the use of geohazard mapping over time, including potential financial, environmental, educational, and health effects - is clearly

2The economic rationale for discounting is twofold: firstly, capital tied up in any project has a potential value, or 'opportunity cost' in other projects. The scarcity of capital should therefore be reflected as a discount rate applied to the project in question. Secondly, the notion of time preference suggests that people prefer to have money now rather than in the future, with the result that future amounts are 'worth less' than present ones.

3The project selection criterion is to accept projects with a net present value of zero or greater when discounted at a suitable discount rate.

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beyond limits of most CBA. For this reason, it is suggested that attention is focussed on discrete land use decisions that might be affected by the availability of new or improved geohazard information. In this context, the fundamental consideration is what impact the application of geohazard information has in the process of land use decision-making, and whether the information would be compelling enough to alter a decision.

Two types of analytical approach to these considerations are possible:

e ex ante analysis, which considers future (hypothetical) decisions that might be made with the geohazard information, against hypothetical decisions that might be made without; and

ex post analysis, which looks back in time to consider improvements that have actually accrued from the use of the geohazard information, through comparison of actual land use decisions made with the information, against hypothetical decisions made without.

Nature and distribution of benefits

For both types of analytical approach, benefits can be defined in terms of costs avoided when land use decisions are improved. Cost savings may take a number of different forms, and may accrue to a variety of different parties. For example, land subsidence costs arising from groundwater exploitation in gypsum areas might fall on homeowners, businesses, municipal authorities responsible for road and sewerage repair, and farmers whose land is threatened by flooding (Box 8). All stand to benefit if land subsidence can be avoided, though there may be a price to pay. For example, relocating municipal water well fields to out of town areas, or substituting groundwater for surface water supplies, may incur higher water supply costs. Costs may be borne by a water utility, or passed on to customers, not all of whom may have benefited from the decision (not all customers may live in areas which are vulnerable to subsidence). Thus, the distribution of costs and benefits between different parties may differ, and it is important that these are spelled out.

5.5 Estimating net benefits

The objective of the analysis is to determine net benefits. Over time, these can be determined by subtracting costs (in terms of hazard map production expenditure) from benefits (in terms of losses avoided). A net benefit stream can then be estimated and discounted to give present values of future amounts.

Illustrative example

In Box 8, the CBA approach to geohazard decision making is illustrated with reference to a hypothetical land use decision. In this illustration, some of the costs -benefit parameters of alternative water supply decisions are identified, together with the different parties they fall on. The benefits of hazard map production are estimated by comparing the cost of groundwater abstraction in a gypsum area - including the environmental costs of land subsidence - with the cost of supplying water from an alternative ‘next best’ source. Both options are assumed to

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Box 8. Cost Benefit Analysis (CBA) framework for assessing geohazard avoidance: alternative water supply options.

COSTS

A. Without hazard map

cost Cost distribution

Cost of distributing and maintaining existing survey mapping information (net of any sale revenue)

Government, via geological

B. With hazard maP

cost Cost distribution

Cost of producing, distributing and survey maintaining geohazard mapping information (net of any sale revenue)

Government, via geological

Includes:

-data collection

-data compilation and interpretation

-data presentation

-printing and publication

BENEFITS

C. Without hazard map

cost Cost distribution

Cost of groundwater supply from gypsum aquifer ($/m3)

Full marginal cost of supply includes:

-investment (capital) and operating (recurrent) costs -public utilityhtility customers

-indirect environmental cost of land subsidence attributable to groundwater flooding risk abstraction

-those affected by infrastructural damage and

-possible user cost if aquifer being depleted

-future users who have to pay for higher cost of alternative

D. With hazard map

cost Cost distribution

Cost of next best alternative water supply Wm3)

Full marginal cost of supply includes:

-investment (capital) and operating (recurrent) costs -indirect environmental cost (eg on downstream users) to environmental assets eg

-public utilityhtility customers

-those indirectly affected by eg by reduced stream flows; damage

wetlands

-possible user cost if non- renewable higher cost of alternatives

-future users who have to pay

The Cost Benefit Analysis (CBA) approach to geohazard decision making is illustrated here with respect to a hypothetical land use decision. The tables compare the parameters to which costs should be attributed of hazard map production and the related decisions about groundwater supply and subsidence problems versus the provision of an alternative water supply and mitigation of the problems. Net benefits, in terms of costs avoided, are calculated by subtracting the additional costs of producing the geohazard information (B-A), from costs saved in relocating water supplies (C-D) to avoid gypsum geohazards.

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provide equal benefits in terms of the quantity and quality of water supplied, thus any decision is based on cost effectiveness. Net benefits arising from the use of hazard map information can then be estimated by subtracting the additional cost of producing the geohazard mapping information, over and above the cost of maintaining and distributing existing information.

Several points in Box 8 emerge:

0 gross and net benefits can be calculated as follows: gross benefit = (C-D); net benefit = (C-D)-(B-A);

the aim is to estimate yearly incremental net benefits. These can then be discounted at a suitable discount rate (consult government ministry/World Bank Office) to give a net present value (NPV) of project (hazard mapping) worth. The key issue is whether the result would change the water supply decision ;

it is important to note that the analysis is conducted from the perspective of society (the national good), rather than from the viewpoint of an individual party, such as a water supply utility or company. Only in this way can wider costs and benefits be captured;

there are considerable practical difficulties in estimating costs attributable to pumping induced land subsidence, as infrastructural darnage may be attributable to a variety of other factors;

supply alternatives should be compared on an equal basis, i.e. for same quantity and quality of water. If the alternative to groundwater is a surface source, additional treatment and engineering costs may need to be included.

an additional level of analysis might also be appropriate in such cases, as an alternative supply-side choice is not the only option available to planners. For example, one way of controlling pumping-induced subsidence is to limit pumping, rather than change the supply source. The cost of implementing demand management options, such as leak detection, recycling and the installation of water efficient devices, would then need to be compared with the cost of ‘doing nothing’ (continuing with the current abstraction regime), which would include the environmental costs attributable to pumping-related land subsidence.

5.6 Synthesis and conclusions

This framework shows how to relate the costs of producing the basic information for hazard avoidance against the potential benefits of avoiding the hazard. No figures have been presented for either the production of the geological hazard maps or the likely savings from hazard avoidance since this is beyond the scope of the present research. However, the size and scale of the gypsum geohazards show that they should be included in geological hazard maps and that hazard avoidance may often be the least costly course of action.

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6. DEALING WITH GYPSUM GEOHAZARDS

6.1 Buildings and construction

The construction of buildings within gypsum karst requires special measures. Construction options for the types of foundations suitable for use in subsidence-prone include raft foundations, j ackable foundations, reinforced strip and special antikarst foundations (Box 9). Difficulties and hazards are present when piling into gypsum karst, or of trying to improve the ground by grouting. The cost of piling to 50m through gypsum on the outskirts of Paris was considered prohibitive, and a major multistorey car park was designed with foundations that would span the 10m predicted size of any new collapses. In additon to these measures, microgravity surveys were carried out and the known cavities were filled; injection tubes were also placed in the foundations to allow for further filling of cavities should they appear. A similar approach to development is the use of extended foundations, or the construction of properties on linked foundations to prevent individual houses collapsing into subsidence hollows (Box 10). Further precautions to these measures, precautions to protect services such as gas, water, electricity and sewerage are also desirable since water leakage can cause severe subsidence (Box 7). These could include protected and flexible pipe work, flexible connections, and protection such as reinforced plastic grid geotextile materials or reinforced supports.

6.2 Development and construction of roads, bridges and railways

Sudden failure of roads over natural and man-made cavities have led to collapses in which vehicles have fallen into the resultant cavity. It is largely impractical to engineer roads with design parameters of sufficient strength to span the larger subsidence features. Even if this could be done, the removal of support from beneath such structures could ultimately result in subsidence features migrating, and the structures themselves failing catastrophically in a much larger way than non-protected structures. One practical approach that was adopted for a new bypass at Ripon was to incorporate several layers of high tenstile heavy duty reinforced plastic mesh geotextile material into the embankments of the road (Box 10). If a subsidence hollow develops beneath the road, the area of the subsidence will sink, but should not fail catastrophically. When subsidence occurs, its location will be obvious and some remedial measures can be undertaken. The use of geotextile materials is also a proven method of protecting car parks and public spaces.

The construction of bridges and viaducts over actively dissolving gypsum karst is problematical. Viaducts around Paris have been constructed with foundations that will span the likely size of collapse, and benchmarks to monitor movement have been installed and surveyed regularly; in addition, a network of clinometers and extensometers are automatically monitored and linked to a warning system which is activated if the settlement exceed 6cm. At Ripon, the new road bridge has been built on the principle of having sacrificial supports (Box 11). The deck of the bridge has been strengthened and built as a continuous structure, so that the loss of support of any one upright will not cause the deck to collapse. A monitoring system to measure the loads on each support has been built into the bridge, and a system installed to warn of any pier failure. In addition to these measures, an added degree of security could be obtained by extending the foundations of each pier laterally to an amount which could span the normal-sized collapses.

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Grouting has been suggested as a method of overcoming the problems of subsidence caused by gypsum dissolution. However, the filling of the cavities may induce groundwater level changes and accelerate the dissolution of the gypsum adjacent to the grouted area, in the same way that a collapse commonly causes dissolution in the adjacent ground and the development of subsidence hollows in groups. Furthermore, in places such as Ripon, where there is a strong artesian groundwater flow and the cavities are large, grouting becomes a very problematical technique. To ensure additional protection, a sulphate-resistant grout will be required to avoid interaction of the sulphate-rich groundwater with the cement-based grout. In contrast to the Ripon area, grouting has been used extensively around Paris for the stabilisation of the gypsum karst along the line of major roads. As a precursor to the grouting, geophysical logging of boreholes has been undertaken using y-ray logging to estimate the degree of cavitation. The success of such grouting schemes is very dependent on the contemporary dissolutional activity and the sizes of the cavities being grouted. All these costs can add a considerable amount to any development; for example, the cost of grouting represented 12 percent of the foundation costs for a new road viaduct around Paris. However, not taking precautions can not only be costly to property and construction, and possibly also to life.

7. RESEARCH TAKE UP AND POSSIBILITIES FOR FUTURE COLLABORATION

The take up of the research can only be accurately judged after all the papers associated with the project have been distributed, assimilated and acted upon. However, the feedback through the numerous meetings and lectures (Appendices 2 and 3) was that most of the people contacted in China did not appreciate the potential for the rapid dissolution of gypsum or the geological hazards associated with it. It is anticipated that the main parts of this study will be translated into Chinese and more widely distributed over the next year or so. In Lithuania, the knowledge of the geological hazards associated with gypsum was much higher. Their understanding of the gypsum karst hydrogeology was greater than the understanding of the more restricted gypsum karst in the UK. However, some of the techniques developed in the UK for the investigation of, and construction in, the gypsum karst areas were considered relevant and useful.

The Geological Survey of Lithuania highlighted possible future collaboration on the mapping of gypsum karst geohazards and the use of Geographic Information Systems (GIS) in engineering geology and planning. These were considered to be the most useful ways of implementing the joint understanding of the gypsum karst problems.

In several provinces of China, requests were made for further studies to be carried out. These included a request for help to understand gypsum collapse breccia pipes which affect coal mining in Shanxi Province. Also requested was help with gypsum geohazard mapping to help with the production of a new geological hazard map of Guizhou Province to be produced over the next four years. In addition to help with geohazards, a request for help to control mine water ingress came from Meishan County in Sichuan Province, this enquiry was forwarded to Geoff Walduck at ODA for advice. Advice on gypsum mining and foreign investment was also requested in Guiangxi Province; BPB industries at East Leake, near Nottingham were informed and meetings with Professor Lu Yaoru (on China) and Dr PaukStys and Mrs Arustiene (on Lithuania) took place.

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8. ACKNOWLEDGEMENTS

This study is the result of cooperation that has been funded by the British Government Overseas Development Administration (ODA) under Technical Development and Research (TDR) contract R6490; Gypsum Geohazards: their impact on development.

In Lithuania thanks go to Dr Bernardas PaukStys of GROTA and Mrs J Arustiene of the Geological Survey of Lithuania for their collaboration. The help and information from the Geological Survey of Lithuania and GROTA is gratefully acknowledged. Thanks go to Drs G.Motuza, J.Satkunas and KKadunas plus all the staff at the Geological Survey of Lithuania for their help and hospitality; special thanks are given to Dr V.MarcinkeviCius for explaining about the gypsum karst in Lithuania.

For the work in China, Dr A.H.Cooper thanks Professor Lu Yaoru for his considerable help collaboration and understanding in arranging the project; Dr Tony Waltham is thanked for his advice and for introducing Professor Lu Yaoru as a co-worker. In China, special thanks for help with this research go to Chief Engineer Wang Guixi, Senior Hydrologist Guo Wenbing, Professor Han Zi Jun, Senior Hydrogeologist Sun Yunzhong, and Senior Engineer Ma Hong Hai, Engineer Xue Zhi Weng, Engineer Tien Jia, Jiang Defu, Associate Professor Xin Fangming and all his staff at the Puding Karst Research Station, and Professor Yang Mingde. Thanks also go to the many other people in the following institutes that helped with the study: Ministry of Geology and Mineral Resources; Institute of Hydrogeology and Engineering Geology; S hanxi Bureau of Geology; Bureau of Geology and Mineral Resources of Yangquan City; Shanxi Geological Engineering and Exploration Institute; Sichuan Bureau of Geology and Mineral Resources; Guizhou Bureau of Geology and Mineral Resources; Guizhou Normal University; Guangxi Bureau of Geology and Mineral Resources.

In England, Drs John Bennett and Tony Reedman are thanked for help in arranging the project. Tim Charsley, John Bennett, Rob Evans, Martin Culshaw, Dr Dave Lowe and Dr Tony Waltham are thanked for reviewing the many manuscript versions of the papers produced by this project.

9. KEY SELECTED REFERENCES

Cooper, A.H. 1986. Foundered strata and subsidence resulting from the dissolution of Permian gypsum in the Ripon and Bedale areas, North Yorkshire. 127-139 in Harwood, G M and Smith, D B (Editors). The English Zechstein and related topics. Geological Society of London, Special Publication. No. 22.

Cooper, A.H. 1995. Subsidence hazards due to the dissolution of Permian gypsum in England: investigation and remediation. 23-29 in Beck, F.B. (Editor.) Karst Geohazards: engineering and environmental problems in karst terrane. Proceedings of the fifth multidisciplinary conference on sinkholes and the engineering and environmental impacts of karst Gatlinburg/Tennessee/2-5 April 1995. 58 1 pp. A.A.Balkema, Rotterdam.

PaukStys, B. 1996. Hydrogeology and groundwater protection problems in karst region of Lithuania. Geological Society of Lithuania, papers, 6, 1-72, Vilnius,

Thomson, A., Hine, P.D., Greig, J.R. and Peach, D.W. 1996. Assessment of subsidence arising from gypsum dissolution: Technical Report for the Department of the Environment. Symonds Group Ltd, East Grinstead. 288pp.

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Appendix 1. Dissemination of information: project publications

Lu Yaoru and Cooper, A.H. In press. Gypsum karst geohazards in China. 1Opp in Beck, F.B. (Editor.) Proceedings of the Sixth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst. Springfield/Missouri/6-9 April 1997. To be published by A.A.Balkema, Rotterdam.

Lu Yaoru and Cooper, A.H. In press. Gypsum karst in China. In A.Klimchouk (Editor) Gypsum Karst, Special Issue of the International Journal of Speleology.

PaukStys, B., Cooper, A.H. and Arustiene, J. In press. Planning for gypsum geohazards in Lithuania and England. 8pp. in Beck, F.B. (Editor.) Proceedings of the Sixth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst. Springfield/Missouri/6-9 April 1997. To be published by A.A.Balkema, Rotterdam.

PaukStys, B. 1996. Angilijos olose lietuviai ieSkojo dimgstanCiy kriokliy, Keliones, Lietuvos Rytas, 20th November, 1996. (Newspaper article, rewritten by the newspaper in a popular format, in the Lithuanian Morning describing Dr A.H.Cooper's visit to Lithuania and the visit by Dr B.PaukStys, Mrs J Arustiene and Professor Lu Yaoru to Great Britain).

In preparation:

Cooper, A.H., Lu Yaoru, PaukStys, B., Arustiene, J. and Calow, R. In preparation. Strategic, local and site specific planning for gypsum geohazards: with examples from China, Lithuania and England.

Associated publications relating to the collaboration instigated by the project

Cooper, A.H. In press. Gypsum Karst of Great Britain. In A.Klimchouk (Editor). Gypsum Karst, Special Issue of the International Journal of Speleology.

Klimchouk, A., Forti, P., Andrechouk, V. and Cooper, A.H. In press. Gypsum karst of the world: a brief overview. In A. Klimchouk (Editor). Gypsum Karst, Special Issue of the International Journal of Speleology.

PaukStys, B. and Narbutas, V. In press. Gypsum karst of the Baltic States. In A.Klimchouk (Editor). Gypsum Karst, Special Issue of the International Journal of Speleology.

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Appendix 2. The collaborative framework for the project

Collaboration with Lithuania

Work in Lithuania was undertaken with two collaborators; Dr B. PaukStys, formerly of the Geological Survey of Lithuania, but with GROTA at the time of the study, and Mrs J Arustiene of the Geological Survey of Lithuania. Work in Lithuania lasted two weeks and involved meetings in Vilnius at the Geological Survey of Lithuania with their Director, geologists and hydrogeologists. The problems of gypsum dissolution, water abstraction, subsidence and planning in Lithuania were discussed and compared with those of the UK. In Lithuania the main gypsum karst subsidence area are in the north of the country around Pasvalys and Biriai. Field studies in the subsidence areas were organised and led by Dr PaukStys and Mrs Arustiene.

Pasvalys. At Pasvalys meetings were held with the Deputy Mayor and the town architect to discuss the problems of subsidence and the difficulties of planning for them. Several examples of gypsum-rich springs and subsidence-damaged buildings were examined. In the past, some precautions against collapse were taken for public buildings, but since the downfall of communism there has not been funding available to avoid the problems. Furthermore, in the free economy many people had started to build and not been able to finish the construction because of escalating costs. Against this background it is difficult to legislate to ensure that the problems of subsidence are mitigated against in the design of foundations and the construction of buildings. However, legislation has been put in place by Government Decree to protect the groundwater of the karst area from pollution by agriculture and other contaminated water. It is feasible that, as the economy of the country grows, legislation (either local or central) could be formulated to take into account the problems of gypsum geohazards.

B i r k i . Water sampling and monitoring techniques were studied in the vicinity of the subsidence- affected town of Biriai. At Biriai, a meeting was held with the Director of the Tatula Board, the regulatory board for the protection of the gypsum karst area. The prognosis for the area here and around Pasvalys is that the continued abstraction of groundwater will lead to enhanced dissolution of the gypsum, the drawdown of the water table and the triggering of more subsidence. The area relies heavily on groundwater, but the provision of alternative supplies, perhaps abstracted from a wider area, may be one way of reducing the impact of the gypsum dissolution subsidence.

Collaboration with China

The principal collaborator in China was Professor Lu Yaoru of the Institute of Hydrogeology and Engineering Geology (part of the Ministry of Geology and Mineral Resources). Work in China lasted three weeks and involved about 60 geologists and administrators in the study which looked at potential problems in four provinces. Information was exchanged at numerous meetings and three lectures on the problems of gypsum dissolution geohazards were presented. Details of these meetings are included in Appendix 3.

Beijing: In Beijing, meetings about the project were held with senior administrators: Professor Zhang Zhenguo, the Deputy Director of the Department of Geological Environment at the

25

Ministry of Geology and Mineral Resources; Professor Zhao Xun, Vice President of the Chinese Academy of Sciences and Secretary-General of the Geological Society of China.

Shanxi Province: Within Shanxi Province, studies were made of the widespread, gypsum karst and limestone karst in the Ordovician rocks. In many parts of the province these underlie the Carboniferous coal-bearing strata. Palaeokarst subsidence breccia pipes are numerous and these commonly penetrate the overlying coal sequences leading to very difficult mining conditions with water bearing breccias being encountered. Some ongoing gypsum dissolution and possible subsidence are also present, but this is largely difficult to separate from subsidence caused by coal mining. Water abstraction through gypsiferous sequences may be a potential problem in the province. The Shanxi Department of Geology and Mineral Resources would like further collaboration to try to understand the gypsum palaeokarst and predict the distribution and pattern of the problem areas in the coal mining region. This would be of great benefit to the economic development of the coalfields.

Sichuan Province: In this province, problems associated with the soluble rock mirabilite (N%SO,. 10H,O) were examined near Meishan. Most of the subsidence problems are caused by severe water ingress and pumping from mining, but natural dissolution could also be a problem. Mirabilite is prone to more rapid natural dissolution than gypsum and constitutes a similar geological hazard. In addition, pumping of minewater, and the lowering of the local groundwater level has caused considerable local subsidence and the loss of local groundwater drinking supplies.

Guizhou Province: This province is famous for its magnificent limestone karst scenery, but it also has gypsum karst problems. The province is poor, with marginal agriculture; it has been designated as a development region in an effort to improve the local living standards. The Guizhou Bureau of Geology and Mineral Resources is to play an increasingly important role in the development of the province by the provision of new geological hazard maps over the next four years. Gypsum karst geohazards were studied at the Puding Karst Institute; the problems include subsidence areas associated with karst water springs that are high in dissolved sulphate. In addition to these problems, a dam is leaking water through the gypsiferous sequence beneath it dissolving the rock as it does so. This research will provide information that will help the province plan for gypsum geohazards. The directorate of the Bureau of Geology and Mineral Resources requested further help on the subject and other geological hazards, to help with the formulation of their geohazard planning maps.

Guangxi Province: In Guangxi Province, gypsum was examined in two areas. Around Lingshan (ESE of Nanning), it comprised only fibrous veins in mudstone and constitutes a minor geological hazard. In the second area near Hepu, the gypsum forms thick seams at a depth of between 80 and 130 metres and possibly comes near to outcrop. Gypsum geohazards may be predicted from the outcrop pattern, but none were observed. The initiation of mining and possible dew atering of the gypsiferous sequence give rise to questions about potential subsidence; this concern was raised with the mining area administrators.

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Reciprocal visits to the UK

The reciprocal visits to the UK for Dr PaukStys and Mrs Arustiene lasted 2 weeks; Professor Lu Yaoru came for 3 weeks. Initial meetings were held with the directorate of BGS, and 6 days were spent looking at gypsum and limestone karst in the field. Gypsum exposures and the effects of dissolution by the River Ure were examined at Ripon, North Yorkshire. Subsidence damage, surface subsidence, investigation and remedial measures were studied around the town of Ripon. At Darlington, the subsidence effects of the gypsum karst were examined, and the water monitoring network being installed was visited. On the Durham coast, Dr D.B.Smith demonstrated cross-sections through ancient (palaeokarst) subsidence pipes caused by the dissolution of very thick gypsum; these are very similar to structures at Ripon, in Lithuania and in China. A short time was also spent looking at limestone karst features to compare them with the gypsum karst. This was to see if the two could be directly compared and thus allow the extensive limestone karst data for China to be used as a predictive model for gypsum karst generation. On return from the field, a visit was made to the BGS Hydrogeology Group in Wallingford for discussions about projects they have undertaken in Lithuania and China. Professor Lu Yaoru spent most of the last week of his visit preparing manuscripts for the publication of the study.

Collaboration with Spain

A one-week visit to study gypsum geohazards in northern Spain, hosted by the University of Zaragoza, was made in June 1996. It was fully funded by the EU through the Commission Mixta, an organisation for scientific exchange. Two lectures on gypsum geohazards, including details about this research, were given to the University of Zaragoza and to the Society of Civil Engineers of Aragon. In addition to lectures, four days were spent studying gypsum subsidence problems in Zaragoza and the surrounding area. The findings of this ODA research are of relevance to planning and development in the Spanish gypsum karst areas.

Collaboration with the Ukraine

Exchange of information about gypsum geohazards has also taken place with Dr A Klimchouk of the Ukraine Academy of Sciences. Papers about gypsum karst in Great Britain, Lithuania and China, generated as a result of this ODA project collaboration (Appendix l), have been accepted for inclusion in a special volume on gypsum karst being published by the International Journal of Speleology. The Ukraine has many gypsum geohazards associated with its extensive gypsum karst. The results of this ODA study are of direct relevance there.

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Appendix 3. Dissemination of information: project meetings, seminars and lectures

Lithuania Geological Survey of Lithuania (meetings with the directorate and geologists) GROTA Hydrogeological Company (meeting with director) Deputy Mayor and town architect in Pasvalys (meetings and fieldwork) Tatula Board (the gypsum karst management board in Biriai; meeting) British Embassy in Vilnius (meeting with Aid Secretary)

China Beijing, Professor Zhang Zhenguo, Deputy Director, Department of the Geological Environment, Ministry of Geology and Mineral Resources (meeting). Beijing, Professor Zhao Xun, Vice President of the Chinese Academy of Sciences and Secretary General of the Geological Society of China (meeting). Shijiazhuang, Professor Dong Fengqi, Deputy Director of the Institute of Hydrogeology and Engineering Geology (meeting). Yangquan, Mr Ma Hong Hai, Director, Shanxi Geological Survey (meeting and fieldwork). Taiyuan, Mr Chen Lian Li Liesen, Director, Shanxi Geological and Engineering Exploration Institute (meeting and fieldwork). Taiyuan, Professor Xiao Jingying, Director, Shanxi Bureau of Geology and Mineral Resources (meeting, followed by lecture to staff on gypsum geohazards). Chengdu, Mr Guo Wenbing and Mr Xu Zhi Weng, Sichuan Bureau of Geology and Mineral Resources (meeting and fieldwork). Guiyang, Mr Han Nan Zhou, Deputy Director; Professor Han Zhi Jun, Guizhou Bureau of Geology and Mineral Resources (meeting and fieldwork) Guiyang, Professor Xiong Kangning, Professor Yang Mingde, Professor Jiang Xinrong, Professor Cheng Xing, Guizhou Normal University (meeting and lecture on gypsum geohazards to staff and students). Puding, Mr Xin Fanming, Director, Puding Karst Institute (meetings and fieldwork) Nanning, Mr Sun Yun Thong, Director, Geological Environmental Management, Guanxi Bureau of Geology and Mineral Resources (meeting and fieldwork). Nanning, Mr Chen, Guanxi Bureau of Geology and Mineral Resources (meeting and lecture on gypsum geohazards to staff).

UK British Geological Survey, Wallingford (lecture on Karst in China by Professor Lu Yaoru and meetings of the whole team with BGS Hydrogeology Group) Nottingham Trent University (lecture on Karst in China by Professor Lu Yaoru)

USA Two papers are to be presented at the Sixth Multidisciplinary Conference on Sinkholes and the Engineering Significance and Environmental Impacts of Karst, Springfield, Missouri, 6-9th April 1997. This meeting has speakers from many parts of the world including China and Russia. Attendance at this meeting has been sponsored by the ODA. The papers are:

Lu Yaoru and Cooper, A.H. Gypsum karst geohazards in China.

PaukStys, B., Cooper, A.H. and Aursteine, J. Planning for gypsum geohazards in Lithuania and England.

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