Yuan Daoxian (China)

ABSTRACT:  The construction of underground dams on subterranean  streams  in karst  regions of China has gained momentum in recent years, because it  entails lessengineering  work and yields quicker results in the supply  of  irrigation water and electric power.

In  South China, karst water is very unevenly distributed and its  flow  and storage mainly  take  the form of subterranean  stream,  so  that  subterranean reservoirs generally have a very limited capacity. But small water  conservancy projects  exactly serve the needs of irrigation and electricity supply  in  the karsts,  where  the landform is characterized by Fengcong  Depression  (cockpit) with  the  farmland  and villages scattered in  closed  depression.  There  are different types of underground dams: full dam, semi-dam, underground  reservoir, surface reservoir (cockpit storage) and others.

Their construction projects should be based on regional hydrogeological data and the  planning  of the subterranean stream system, with due  care  given  to leakage prevention, flood control, and water supply at upstream and  downstream points.

One  of  the  most concentrated karst region in the world  lies  in  Yunnan, Guizhou, Sichuan, Hubei, Hunan, Guangxi provinces and their neighbouring  areas in Southwest China. It covers a continuous area of 500,000 km². The  thickness of Carbonate rock there reaches 3,000-10,000m, which distributes  predominantly in  the intervals  from Sinian to Ordovician, and from  Devonian  to  Triassic. Annual precipitation reaches 1,000-2,000 mm, but about 70% of it is concentrated in the rainy season from May to August. Annual mean temperature is 12-22° .

The  fundamental  characteristics of landscape are controlled by  the  great intermittent  uplift  in  the  Cenozoic era. Apart from  the  wide  exposure  of carbonate rock,  peneplains  with altitudes from 500-2,500m  are  dissected  by gorges of the networks of the Changjiang and Xijiang rivers. The bottoms of  the gorges are cut down to an altitude of 50-900m.

All  the conditions mentioned above are favorable for the rapid  circulation of underground water and intense development of karst. They also bring about the great unevenness of spatial distribution of karst water, which stores and flows mainly  in the  form  of  subterranean  stream  (conduit  flow).  According  to preliminary statistics, there are 2836 subterranean streams each with a  minimum flow of more than 0.05 m³/s in South China (Fig.1). The total minimum dischargeof these subterranean streams is 1482 m³/s, and their total length is 13,919 km. However,  the characteristics  of  conduit  flow  and  unevenness  of  seasonal distribution of precipitation give rise to the great amplitude of fluctuation of subterranean  streams,  which  have  a seasonal variation  of  10-100  times  in discharge and tens to over 100 meters in water table. In some karst regions, the depth  of water table reaches tens to hundreds of meters in dry season,  on  the other hand, the closed depression (cockpit) may be flooded in rainy season.  So, artificial control is necessary before these abundant karst water resources  can be utilized.

Fig.1 The distribution of major subterranean streams in South China karst
1. bare karst; 2. buried karst; 3. non-soluble rock;
4. major subterranean stream.

Hundreds  of  underground  dams  have been built  in  recent  years  on  the subterranean streams in south China, which have solved the problem of irrigation properly  according  to  local natural conditions. For example,  at  the  Xiashi district (Dushan county, Guizhou Province) alone, there are 16 underground dams that capture subterranean streams for irrigating 22,000 mu (one acre=6.07 mu) of farmland. The catchment area of a subterranean stream is small and ranges  from several to tenof square kilometers in general, whereas the largest one reaches more than 1,000 square kilometers. The trunk lengths of subterranean streams are usually several to over ten kilometers, with the largest one probably being over 50  kilometers. The minimum discharge of such subterranean streams  is  0.05-0.1 m³/s in general, whereas thbiggest one reaches 8.9 m³/s. So the capacity  of the  reservoirs formed by dams on such subterranean streams is small and  ranges from  several hundred thousand to several million cubic meters in general,  with the largest one being over one hundred million m³. It follows that the area  of farmland  irrigated  by  such a kind of reservoirs is  also  small  in  general, ranging from hundreds to thousands of mu, the largest one being over one hundred thousand mu.

Fengcong-Depression (cockpit), the typical tropical karst landscape, is  the main feature of South China karst. Villages and farmland are scattered  sparsely on  the bottoms of the karst depressions or poljes which varies  in  size.  The farmland  in each depression has an area of only hundreds of mu, or  even  less than  ten mu. In some large poljes, there are farmland several thousand  to  ten thousand  mu. Moreover, the depressions or poljes are seperated each  other  by cluster  of  peaks with relative altitudes tens to hundreds of  meters  (Fig.2). Evidently,  under  the natural conditions described  above,  building  dams  on subterranean  streams  to form small reservoirs, and  solving  the  problem  of irrigation  for  each  cockpit depression individually,  is an  economical  and rational measure.

Fig.2 Profile across closed depressions along the Beitu subterranean
stream, Hechi county, Guangxi
1. upper Carboniferous, limestone;
2. subterranean stream, water table and altitude.

The  dams  on  subterranean streams may be divided  into  two  major  types, namely,  the  full  dam (damming up the whole cross section  of  a  subterranean stream)  and  the  semidam  (partially  damming  the  cross  section).  However, according  to  their  positions on subterranean streams,  they  may  be  further distinguished into three types as foredam (dam site near resurgence), window dam (dam site near a karst window), and back dam (dam site near the swallow hole and converting a karst depression into a reservoir).

Moreover,  according  to their functions in the  exploitation  project,  the underground dams may be classified as for storing water on surface, for  storing water underground, as well as for raising water table only (diverting water  for irrigation or HE power) and etc. Some examples are followed.

THE YIDONG RESERVOIR. In Huanjiang county, Guangxi. Back full dam, a surface reservoir  is  formed in a depression, with a capacity of one million  m³,  and water head 10m, used for control the subterranean stream to irrigate farmland at the downstream of the resurgence. (Fig.3).

THE YUZHAI UNDERGROUND RESERVOIR. In Dushan county, Guizhou province.  Semi-foredam,  5.97m in height, 9m long and 4m wide on base, 1.8m on crest.  Distance of  backwater  1200m.  Capacity of reservoir is 96  thousand  cubic meters  and irrigates 1,500 mu farmland (Fig.4).

THE   LONGWANGDONG  UNDERGROUND  RESERVOIR.  In  Jiangbei county,   Sichuan province, the subterranean stream is developed in the Triassic limestone of  the axial part of an anticline, and was excavated through by a coal mining tunnel in 1966. The capacity of the underground reservoir as estimated by the total volume of  water  flowed out within 72 days after it was opened is 16.8  million cubic meters. The reservoir was restored in 1972 by damming the tunnel again, with its highest  water  pressure amounting to 6.2 kg/cm², and annual yield of  water  6 million cubic meters (Fig.5).

THE  JIJIAO  UNDERGROUND  DAM.  In Xincheng  county,  Guangxi,  the  minimum discharge  of the subterranean stream is 1.5 m³/s, and the full dam is  at  the downstream  side  of  a  karst window. The water table has  risen  up  19m  (dry season)--30m  (flood  season) since the dam was built in 1958. At  five  hundred meters  upstream from the window, a 49m long diversion tunnel was excavated  for irrigating 2068 mu farmland (Fig.6).

THE  YUHONG SUBTERRANEAN STREAM HE POWER STATION. In Huaihua  county,  Hunan province,  the subterranean stream is developed along the bedding plane  between the limestone and impervious beds. The full foredam (10.5m high, 7m wide, and 3m thick)  is  an  equalthick  arch  dam, which  raises  the  water table  of  the subterranean  stream  34m in dry season and 115m in  flood  season  respectively (Fig.7).

Fig.3. The reservoir on the Yidong subterranean stream, Huanjiang county, Guangxi
1. Middle Carboniferous, dolomite;
2. Lower Carboniferous, sandstone and shale;
3. subterranean stream and dam; 4. reservoir.

Fig.4 The underground reservoir on the Yuzhai subterranean stream, Dushan county, Guizhou province
1. upper Devonian, limestone; 2. underground dam and reservoir.

THE  BEILOU  SUBTERRANEAN  STREAM  HE POWER  STATION.  In  Xincheng  county, Guangxi,  the subterranean stream is developed along the bedding plane,  with  a minimum  flow of 0.15 m³/s. To concentrate and get the 24m high water  head,  a semi-foredam  is  built, and a channel followed by a tunnel is dug  in  cave  to divert water into a HE power station outside (Fig.8).

Fig.5 Longwangdong underground reservoir, Jiangbei county, Sichuan province
1. Middle and Upper Jurassic, red shale and mudstone;
2. Lower Jurassic, sandstone intercalates coal bed;
3. Middle Triassic, limestone;
4. Mining tunnel and underground dam;
5. cross section of subterranean stream;
6. spring.

PROBLEMS THAT MUST BE CONSIDERED IN BUILDING DAMS
ON SUBTERRANEAN STREAMS

1. A comprehensive plan is necessary to have an overall consideration  about problems  of  water supply and flood control for both the  upstream  points  and downstream   points  of  a  subterranean  stream  system.  Before  building   an underground  dam, it is necessary to make clear the course of  the  subterranean drainage system, and consider as a whole the problems of water supply and  flood control  for all the depressions or poljes it passes through. For instance,  the Wanger underground dam, in Dushan county, Guizhou province, is a full foredam 8m long, 9m high,  and 6m wide, with a capacity of  one  hundred  thousand  cubic meters,  but  its backwater is 3000m long, and has influences on  a  series  of depression upstreams (Fig.9), so a special surface spillway is dug.

Fig.6 The Jijiao underground dam, Xincheng County, Guangxi, China
1. Upper Carboniferous, limestone;
2. underground stream and dam;
3. cross section of the artificial tunnel;
4. high water level;
5. low water level.

2. Leakage prevention. Most of the underground dams are small in  capacity, injection  curtain are scarcely used except some larger projects.  The  measures for leakage prevention are usually simple ones utilizing some favourable natural conditions.  Detailed  cave exploration is necessary before damming,  so  as  to select the throat point as the dam site on the basis of the  information  about the  expansion and  connection characteristics of the whole  cave  system.  For example,  the  Neiwan underground reservoir, in Chenxi  county,  Hunan  province (Fig.10) has a very complicated cave system, but it is under the control of  the dam  point  so  it has got a water head of 70 meters and  a  capacity  of  seven hundred thousand cubic meters. For a full dam, leakages around the cave  ceiling must also be taken into account.

Fig.7 Hydroelectric power station on Yuhong subterranean stream. Huaihua county, Hunan province.
1. upper part of upper Permian; 2. lower part of upper Permian; 3. limestone and dolomite; 4. siliceous rock; 5. carbonaceous shale; 6. subterranean stream; 7. underground arch dam; 8. pipe line and HE power station.

Fig.8 Beilou HE power station, Xincheng county, Guangxi
1. Lower Permian; 2. Upper Carboniferous; 3. limestone; 4. underground dam and reservoir;
5. artificial channel and tunnel in cave; 6. pipe line and HE power station.

Fig.9 Backwater of Wanger underground dam, Dushan county, Guizhou province
1. upper Carboniferous; 2. middle Carboniferous; 3. limestone; 4. fault; 5. underground dam and backwater.

Fig.10 Cave system and the dam site on Neiwan subterranean stream, Chenxi county, Hunan province.
1. cave system; 2. underground dam site; 3. water level of the underground reservoir; 4. artificial diversion tunnel.

3. Foundation of dams. The narrow part with sound rocks in the  underground passage is preferred as a dam site, besides, careful treatment is also necessary for those early deposits in a subterranean stream, if they are  distributed  on the  possible  way of leakage, even though they are cemented by  travertine  and look  to  be  very hard. The underground course adjacent to the  upstream  of  a reverse  siphon is often not suitable for damming, because alluvial  deposit  is usually  thick  there. For instance, in such a part of  the  Solue  subterranean stream, Bama county, Guangxi, the cross section is only 13m in width, and  rocks on the cave ceiling or walls are perfect, but the thickness of alluvial  deposit under the stream bed reaches 18.47m, as testifed by drilling.

Kazuko Urushibara-Yoshino (Japan)

In  Japan,  there are 2 types of limestone areas; namely  i)  the  limestone areas older than Tertiary, and ii) uplifted coral reefs during Quaternary  era. The  latter  areas are located mainly on the southern Kikai  islands  in  Nansei Islands. The former areas are located in Honshu and Okinawa Island. These  areas are shown in Fig.1.

As an example of successful natural conservation, quarries in the Palaeozoic limestone  areas  at Chichibu in Central Japan are discussed in this  paper.  An example  of  problematic management of land use in the areas of  uplifted  coral reef limestone  areas is found in Nansei Islands in southwest  Japan.  Further, examples of Ishigaki and Minamidaito Islands are also discussed.

THE RECOVERY OF THE VEGETATION ON QUARRIES

In  the  Chichibu region, there is Buko Mountain  (1,336m  a.s.l,  35° 57¢ N 139° 06¢ E), which is composed of paleozoic limestone layers. This mountain has been  a  religious  symbol  for the local people.  They  made  lime  by  heating limestone blocks from the mountain in the historical age.

The  first  cement factory was opened in this area in 1925 and  quarried  by machinery  using modern methods. The second factory has started  quarries  since 1926. After the war the economic development of Japan caused the rapid  increase in demand  for cement and the 3rd cement factory began quarring  in  1969.  The special railway for the transport of limestone blocks and cements was introduced on the foot of the Buko Mountain.

These factories have produced continuously great amount of limestone  blocks from the  mountains  by the vertical-cutting-method.  The  mountain  shape  has changed due to this and, as a result, the height of the mountain has become  30m lower  in  the years around 1975. During this time there  was  popular  protest against this because the high cement production with the vertical-cutting-method resulted  in  a lot of dust spreading over the city.  Furthermore,  people  felt uneasy  about  the  rapid  change of mountain's shape  as  the  mountain  had  a religious significance for them.

Then,  the  Ministry of International Trade and Industry (MITI),  the  three companies  mentioned  above, which have quarries, and the scientist  group  have investigated together to find a way of recovering the vegetation by introduction of trees  on  the  walls of quarries and decrease the  limestone  dust  in  the Chichibu region since 1972. This action was called "Green Campaign".

Fig.1 Map of limestone areas in Japan.

As  shown  in Fig.2, five ways have been examined on the vertical  walls  of limestone  quarries  in  Japan  by MITI from 1972 to  1982.  Finally,  MITI  has made regulations  in 1982 as follows: 1) The quarrying  companies  should  plant trees in the quarried places, which are usually located on the steep slopes  in Japan.  2) Angle of slopes of the quarries should be smaller than 60° .  3)  The species of plants should resemble as much as possible the original vegetation in the  quarried  area. The soils with similar types to the original  soils  should also be introduced. 4) The steep quarried walls should be cut in steps with  10m height  difference for each. Trees must be planted in the holes with the  soils. On  the steeper walls, vines like ivy should be planted. 5) Each company has  to report  to  MITI  every  5  years with pictures of  the walls  covered  by  the vegetation.  If the companies fail to keep this regulations, they will  not  get permission from the government to operate in future.

Fig.2 Tested five techniques for recovering vegetation on the walls of  quarries.

At  present, this regulation works very well. From the "Green Campaign",  we learned  that  the supply of some soils on the bare limestone  walls  helps  the development  of  vegetation  very  much, particularly  at  the  first  stage  of recovery.

The  southern  islands  of  Okinawa  Prefecture  reverted  to  the  Japanese Government  from  the  occupation  by  U.S.A. in  1972.  After  that,  the  land reclamation  in  the  huge  areas  started with  the  support  of  the  Japanese Government and the local office of Okinawa Prefecture. In Nansei Islands,  whose southern  part  is  in  Okinawa  Prefecture,  the  most  serious  problems   for agriculture were drought. This occurs almost once in three years. The  strongest crop during the dry summer is sugar cane and the farmers' income is the  highest because of its price. Due to such reasons, on almost all the islands, sugar cane was mainly cultivated.

The lowest yields of the sugar cane during the drought occurred in the areas with Quaternary  uplifted coral reef, because the soils here  are  shallow  and there  is heavy clay in these areas. Then, the government decided  to  introduce irrigation systems and to put lot of soils formed from Tertiary mud  stone  in these  areas.  For the sake of using big machines the unit size  of  fields  was increased.

The  reclaimed  areas on Ishigaki Island since 1975 is shown in  Fig.3.  The yield after the land reclamation since 1975 increased only 6% as compared  with the average of period (1960-1977) (Fig.4), even though the sprinkler system  was introduced  to the fields. This percentage is not satisfactory, if  we  consider the  cost incurred for the land reclamation. In addition, the  present  fringing coral reefs have been damaged by soils, which are transported from the fields by rain  wash.  The coastal fishery is having  serious  problems;  in  particular, catching  shrimps and eels has been affected seriously because they  prefer  the clean sea water in coral reefs.

Because  Minamidaito Island is a paleo-atol, thick red soil exists and  this condition has made it possible to continue monoculture of sugar cane. It was not necessary to introduce the other soils for the land reclamation. However,  since 1972, because of the control by the government the farmers in this island  could not  employ the workers from abroad. Instead of hand harvest by  those  workers, the farmers had to introduce the harvesters and accordingly, the land units were arranged for easy work for harvesting sugar cane continuously until now. Against drought,  the  drop-irrigation system from the caves has been introduced.  As  a result, in the several caves, the ground water has become saline. This has  been caused  by inadequate  self-management  by the  farmers.  The  introduction  of harvesters  to the sugar cane fields made the soil layers harder. As  a  result, productivity  in  the serious drought years became lower than  before  the  land reclamation and introduction of harvesters.

Fig.3 The land reclamation areas and distribution of red soils on  uplifted coral reefs at Ishigaki Island.
1. Red soils on the rocks except uplifted coral reefs;  2. Red soils on the uplifted coral reefs; 3. Alluvial soils.

Fig.4 Relationship between sugar cane yield and water deficit at  Ishigaki Island.

QUANTITY AND QUALITY DEGRADATION OF UPPER JURASSIC AQUIFER IN OLKUSZ-ZAWIERCIE KARST REGION (SOUTH POLAND)

Wieslawa Krawczyk, Marian Pulina, Andrzej Tyc (Poland)

Cracow-Czestochowa Upland is the biggest karst region in Poland (about 3,500 Km²).  Together  with the karst region of Silesian Upland it  enjoys  the  main aquifer  of  Silesian-Cracow  monocline.  This  region  is  of  importance   to hydrological balance of the whole country also. It is the main zone of  recharge of  surface  water apart from the Sudety and the Carpathy Mts. Here,  there  are important  springs  on the Vistula and the Odra  tributaries  (the  Warta,  the Pilica, the  Przemsza). So this karst region controls quantity  and  quality  of South Poland river's waters and underground water intakes.

Considerable  part of Cracow-Czestochowa Upland, with  the  Olkusz-Zawiercia karst  region as its main part, is under influence of Poland's  greatest  urban-industrial district  of Upper Silesian. The  country's  greatest  metallurgical works  "Katowice" and  zinc-lead mines "Olkusz-Pomorzany" are  in  the  nearest vicinity  of  the Olkusz-Zawiercia  region. This  region  is  also  intensively cultivated.

In  this  conditions underground water resources are reduced  and  intensive quality degradation is observed. The authors should like to describe  the  main elements  of anthropogenic degradation of the Upper Jurassic aquifer  and  show basic  factors causing this degradation in karst region. Presented  results  are based  on  several years of hydrological  and  hydrochemical  researches  being carried out at the Department of Karst Geomorphology of Silesian University.

Olkusz-Zawiercie  karst region belongs to the complex of  underground  water aquifers  in the Silesian-Cracow monocline. It is connected with Upper  Jurassic banded,  rocky  or  chalky limestones occuring on the surface or  under  a  thin cover of Quaternary deposits (Fig.1). Their thickness varies between 50-400  m, but  it reaches  90 m on the southern end and 120-150 m  on  the  north-eastern border of the study area. The Upper Jurassic limestones build aquifer  which  is fissured and karstified through the whole profile. The system covers three  main mediums  of  water  circulation:  (1) porous, which  in  natural  conditions  of hydrodynamic  regime,  may  be treated as not active, being a  medium  of  water storage, (2) fissured, which is the most effective hydraulic system of the whole massif, varied depending on a lithofacial level of Jura, (3)  channel  (karst), which  is the most effective in the vadose zone (Liszkowska, Pacholewski  1989). Small  conduits (several mm to several cm in diameter) and fissures  widened  by corrosion, which may be found through the whole profile of limestones, are basic karst  forms  that  are involved in water circulation.  Caves  and  caverns  are restricted only to the layer close to the surface and they are not hydraulically active.  As most of the fissures and the karst forms are filled  with  sand-clay deposits  the  water-bearing system of the Upper Jura shows, in  certain  deeper parts, characteristic features of the porous system.

Fig.1. A: Location map and    B: geological and hydrological setting of the  Olkusz-Zawiercie karst region.
1. Upper Jurassic limestones on the surface; 2. Upper Jurassic limestones under the cover of sand-clay deposits; 3. Triassic limestones and dolomite, also nonkarstic rocks; 4. springs; 5. rivers;  6. limit of hydraulic depression cone in Middle Triassic aquifer; 7. well at Chechlo (see Fig.2); 8. altitude in m a.s.l.

The  above characteristics proves that water circulation in  Upper  Jurassic aquifers is  rather  diffusive than channel. Because  of  tectonics  and  large erosional dissection the  drainage system in the  massif  between  Olkusz  and Zawiercie is dispersed. It is proved by great density of springs. Some of  them, in  the  western  part of the area, are connected with  Upper  Jurassic  cuesta. Outflows  in the limit of a deep denudational-tectonic dissection of  the  Biala Przemsza  constitute another group of springs. Discharge of majority of them  is below  2.5  l/s and they are very often grouped forming the  zones  of  outflows where total discharge is about 20 l/s. The highest discharge of several  springs reaches  150 l/s. Apart from draining system some water from the Upper  Jurassic massif is drained towards east under the cover of Cretaceous chalk deposits. The whole aquifer is enriched by precipitation through limestone outcrops.

Olkusz-Zawiercie  karst region is strongly influenced by the region of  zinc and lead ores exploitation. Major part of the discussed region is  within  the limit  of  a hydraulic  depression cone of zinc and  lead  mines  (Fig.1).  The depression  covers the subjacent Upper Jurassic, Middle Trassic  limestones  and dolomites, forming a separate fissured-karst aquifer. Stratigraphic Trassic and Jurassic carbonate layers are separated by impermeable Rhaetic-Liassic deposits. However  the  isolation  is not prefect and the levels may  be  in  a  hydraulic contact.  Numerous  erosional  windows in the Rhaetic-Liassic  cover  have  been evidenced  outside the limit of Jurassic limestones, when  such  discontinuities have not been undoubtfully proved within the Jurassic limit. Therefore hydraulic connection between the Upper Jurassic and Middle Triassic aquifers have not been finally  proved  yet. However there are more and more data  suggesting  that  at least  local quantity degradation of Jurassic karst waters exists, which is  the result  of  artificial drainage within the limit of  the  hydraulic depression cone.

Fig.2. A: Linear trend function of precipitations;
          B: Upper Jurassic underground water level fluctuations at Chechlo;
1. trend of precipitation; 2. perennial mean of precipitation; 3. annual precipitation amount;
4. trend of water level of Upper Jurassic aquifer; 5. perennial mean of water level height; 
6. annual mean of water level height; 7. periods of dried well.

This  can  be proved by numerous dry springs, category  changes  of  certain springs of high discharge from permanent to temporary and loss of water in  farm wells.  It occurs mainly to the south-east and east from Olkusz. Fig.2  presents changes occuring in the Upper Jurassic aquifer for the last 20 years. The period covers  natural conditions to the widening of the hydraulic depression  cone  in the  Middle Triassic massif to the north (till 1975) and probable  influence  of artificial drainage. Dynamics of perennial changes in the aquifer are shown  as a function of trend of the the data concerning fluctuations of underground water levels in the well at Chechlo (see 7, Fig.1) and precipitation at the station at the same village. Despite the observed hydrological drought in the whole  Poland in  the  years 1982-1984 the trend of precipitation in the  period  is  slightly increasing.  Similar and even deeper droughts occured also earlier  (e.g.  1969, 1971,  1973,  1976), when the trend of water level fluctuation in  the  well  is diminishing.  As  the  circulation  is diffusive,  till  1982 the water  level oscillated around the mean perennial level, despite distinctive  fluctuation of the total precipitation. In the end of 1983 the well at Chechlo dried completely and even after deepening it remained dry from September 1984 till  March  1985. The divergence of trends of both phenomena proves that significant lowering  of the underground water level in the Upper Jurassic aquifer does not result  only from hydrometeorological  conditions in the last few years. It may  be  assumed that  the well  at Chechlo is probably influenced by  the  artificial  drainage connected  with the zinc and lead mines. The influence of the drainage  is  the most intensive and troublesome in the periods of hydrological droughts.

General  physicochemical properties of karst waters in the  Olkusz-Zawiercie region  are presented in Fig.3. Waters from spring in this area are of  calcium-hydrocarbonate type. The only exception are the waters from two springs  located outside  the  range of the Upper Jurassic limestones (10,11,  Fig.3)  where  the waters  are of sulphate-calcium type. Waters in the northern part of the  region contain  large  amount of  sulphates when  highly  mineralized  waters  contain chlorides  and nitrates. Water from farm wells constitute a separate group.  Two types  of wells can be distinguished: (1) where water properties are similar  to moderately mineralized springs; (2) where water is more intensively  mineralized with  the  value  of specific conductivity reaching 125 ms/m.  Large  amount  of nitrates,  chlorides,  sodium  and potasium in the ionic  composition  of  these waters is a characteristic features (29, Fig.3).

Waters   of   the  Upper  Jurassic  aquifer  are  characterized   by   large diversification  in  specific  conductivity. It can  be  proved  by  significant diversification  of  the  contents  of elements  being  the  effect  of  natural processes of limestones dissolution related to foreign elements, the results  of anthropogenic impact. Strict dependence of conductivity value upon the amount of calcium  ions  and hydrocarbonates is connected with the ionic type  of  waters. Simultaneously,  increase of  specific  conductivity  is  accompanied  by   the increasing  number of ions of anthropogenic origin in the ionic  composition  of the water (sulphates, chlorides, nitrates) (Fig.4). This dependence is fulfilled at the high correlation coefficient. Hence, anions of anthropogenic origin  play the  crucial  role  in  the ionic composition of the waters  from  the  highest mineralized springs. Therefore specific conductivity in the springs draining the same aquifer can be a good indicator of degradation in its different parts.

Fig.3. Hydrochemical characteristics of Olkusz-Zawiercie karst region.
1. springs; 2. farm wells; 3. rivers; 4. forests;
5. ionic composition of water (diagram radius shows the specific conductivity value).
Numbering as in text and Fig.4.

CONCLUSIONS

Basic  reason of the significant lowering of the underground water level  in the Upper Jurassic aquifer is the artificial drainage connected with the mine's hydraulic depression cone. The reasons of significant transformation of  natural chemical composition  of the waters in Olkusz-Zawiercie karst region  are  four basic factors: (1) intensive rain waters pollution; (2) location of villages  in the  highest  parts  of  the karst massif  and  lack  of  sewage  systems;  (3) fertilization  (main  nitric)  in agricultural area;  (4)  fissured-karst  water circulation  system  in  vadose  zone of  the massif,  which  makes  pollutants migration easier.

Fig.4. C--Dependence of specific conductivity;
å A--upon the amount of anions of anthropogenic origin (SO₄^2-, Cl^-, NO₃^-)
1. spring waters; 2. waters from farm wells.
Numbering as on Fig.3.

Because  of the main direction of air circulation from the  urban-industrial Upper Silesian region rain waters reaching the Olkusz-Zawiercie karst region are intensively polluted. They contain considerable quantity of nitrates, with  mean concentration  in the  rain water reaches the nitrates  content  in  moderately polluted  spring waters (15.5 mg/dm³) (see R. Fig.6). Several times in  a  year precipitations with nitrates content above 50 mg/dm³ appear (Fig.5, 6).

Influence   of   the   rain  water   pollution   has   regional   character. Diversification of degradation degree of the Upper Jurassic aquifer is caused by two other anthropogenic factors. The lack of sewage systems results in very  bad quality  of water in farm wells (40-50 m deep in this area). Wells developing  a hydraulic depression cone are the place of pollutants intrusion into the aquifer (liquid  manure and sewage). Bad water quality of springs situated  in  greater villages  has the similar origin. That waters have higher  mineralization,  high chlorides and nitrates content, and low oxygen saturation degree (e.g.C, Fig.6). Furthermore, most degradated waters emerge from springs in the regions of  farms influence. From mineral compositions introduced with fertilizers into the  soil, nitrogen  in  nitrates  forms  are easily washed  to  underground  water.  Hence distinct nitrates content occurs in underground waters of northern parts of  the study area, which are influenced by highly fertilized farm grounds. That  waters contain phosphates, too.

Fig.5. Seasonal variability of nitrates content in spring and rain waters.
A, B--spring I and II at Ryczowek (18,19, Fig.3);
C, D--spring I and II at Klucze (6,5, Fig.3)
R--rain waters from Sosnowiec
(based on unpublished data of M Lesniok--Silesian University).

Fig.6 Average (circle) and range of select physicochemical properties  of Upper Jurassic waters.
A,B,C,D,R--explanation as on Fig.5. C (ms/m)--specific conductivity;
O₂(%)--diluted oxygen content; Cl^-(mg/dm³)--chlorides content;
NO₃^-(mg/dm3)--nitrates content.

K.A.Gorbunova,N.G.Maximovich
V.P.Kostarev,V.N.Andreichuk (USSR)

The  Perm  Region  territory of 1606 sq.km is situated  within  three  large geotectonic units: the eastern margin of the eastern European platform,pre-Urals foredeep  and  the  folded  belt of the Urals  zone.  The  Paleozoic  karstified rocks:limestones,dolomites,gypsums,anhydrites,salts  are  exposed or  occur  not deep from  the  surface  on the area of about  30  thousands  sq.km.  Numberous boreholes in the carbonate rocks have revealed paleo-karst.

The  karstified  rocks  occur in the form of anticline  and  syncline  folds accompanied  with  fracture  dislocations.  Typical  are  sinkholes,  solutional basins, lost rivers, springs, caves and blind creeks.

Perm  region  bears a considerable technogenic load.  The  distribution  of various types of technogenic effects on the environment is conditioned by  the presence  of commercial  mineral  deposits,timber  and  water  resources , the geographic position of the region on the border of the western and eastern areas of  USSR,the history of its development. The greatest changes of the  geological medium  of the karst areas are caused as a result of various types of the  human economic activities, such as: 1) mining industry (Kizel Coal Basin,Verkhnekamskoye Potash  Salts  Deposit,Volgo-Urals Oil and Gas Bearing  Area); 2)  hydrotechnical construction  (Kamskaya hydroelectric station and Kamskoye reservoir); 3)  urban and industrial construction (on the basis of commercial mineral  deposits,timber and  water  resources in Perm Region there appeared large  industrial  centers--cities  of  Perm, Berezniki, Kizel, Chusovoy and others); 4)  communication  and transport  constructions  (the region is crossed by railway and  highway  lines, electric  transmission  lines,oil  and gas pipelines);  5)  water  distribution systems  (use  of  fresh drinking,medicinal and commercial  mineral  water);  6) timber  industry and agricultural activities (tree felling,chemical effect  from agriculture).

All these kinds of the human economic activies change some components of the environment  (overburdon  and karstified  rocks,relief,underground  and  surface waters, atmosphere, biosphere) which is reflected directly or indirectly on  the basic conditions  for karst develoment and causes its activition  or declining.

In   many   construction  types,mining,guarrying  (especially   gypsum   and limestone) the soil cover blanket deposits are removed partially or entirely,the karstified  rocks  are  exposed. In some cases,the removed  soils  are  used  in construction  forming media aggressive to karstified rocks. In other cases,  the solid waste  disposal  consist of soluble  minerals.  The  constructions  being erected   and their   operation   create   static   (industrial   and    civil objects,reservoirs)  and dynamic loads (blasthole  drilling,intensive  transport traffic).

The  consequence  of  these  types of economic activity  is  change  of  the stressed condition  of  karstified  rocks,  their  fracturing,  formation   of technogenic landscape,  appearence  of  concentrated  absorption  centers   of atmospheric precipitation and karst waters rechange.

The  activation  of  karst  caused  by the  disturbance  of  the  cover  and redistribution  of the surface run-off was observed in the area of the main  gas pipelines  Siberia-Center-West. They cross the western limb of the Ufa swell  to the south of the city of Kungur where are karstified gypsums and anhydrites,  to a less degree the limestones and dolomites of the Kungurian stage. There can  be traced  a connection  of  the  karst  and  the  river  network  with   tectonic dislocations. Most karstified area are the sites where the gypsums are  exposed or  covered with soil vegetation layer or eluvium of small thickness.The  number of sinkholes for 1 ha here reaches 95, the area of sinkholes totals 50 per cent of the site area. The initial size of the collapse sinks is 2 to 3 m,the average diameter  of the sinkholes is 7 to 8 m.From May 1983 to October 1984 in the  gas pipeline area of 40 m wide and 5.4 km long there appeared 24 collapse sinkholes, and  in  1985 their number exceeded 45. A great part of the collapse  sinks  had diameter of no more than 2.5 m,depth of 2 m and only in some cases 5 m.

At  present,  such collapse presented no danger, but further  activation  of collapse may have negative sequences. To provide safety of construction and  gas pipelines, antikarst  measures were recommended: filling the karst  sinks  with non-draining material,  arranging of the surface waters run-off,  reduction  of transport load,stop of blasting operations in the pipeline area.The condition of the constructions is being monitored.

Intensity of the collapse process increase after construction of  industrial and  civil objects and roads,the collapse sizes being increased.  For  example, from  1960  to 1971 in Kungur region in road-side ditches  and  reserves  there appeared 22 collapse.

In  quarring of limestones and gypsum the overlaying deposits  are  removed. Blasting  operations  in quarries lead to fracture forming and  opening  in  the rocks which promotes infiltration of atmospheric precipitation.The suffosion and dissolution activation causes numerous suffosion-karstic collapses, for example, in the vicinity of the gypsum quarry Yergach to the north-west of Kungur.

The karst activation is caused by variation regime of the level and chemical composition  of the karstic waters in the water intake areas,in mine and  quarry outfall and  drainage  system.In  these  cases, the  hydrodynamic  zones   are shifted,the karstic water flow direction changes and the velocity increases.

In Kizel Coal Basin the coal-bearing strata of the Visean stage of the Lower Carboniferous  series  occurs under the karstified carbonate rocks.  Some  mines passed  through  cavities and caves filled with water. In  the  karst  influence zone,the mine water inflow reach 2000 to 2500 m«£/h. As a result of  the  karst waters drainage thick strata of carbonate rocks are involved in the active water exchange and karstification. In interaction with sulfur-containing  coal-bearing rocks,the  bicarbonate karst  waters are  transformed  into  bisulphate  waters enriched  with ferrum,aluminium and other microcomponents. The mine  waters  run down  into rivers  and are partially absorbed by  ponors.  Moving  along  karst channels in carbonate rocks the bisulphate (PH 3 to 4) polluted mine waters  are partially neutralized and cleaned. In the southern part of the basin  the  mine waters  are released into the river Gluhkaya which disappears in the  cave  and flows  for 7 km by underground route. The river feeds a spring in the valley  of the river Chusovaya whose freshet discharge reaches 10 thousand m«£/h. After the mine waters passing through the underground karst channels the ferrum, aluminium and  sulphate concentration reduces ten and hundreds of time. At the  same  time there  occurs contamination of stalactites and stalagmites in caves with  ferrum hydroxides. Some cavities are filled by sediments.

The recharge,circulation and outflow conditions and the chemical composition of karst  waters change considerably in the influence  zones  of  hydroelectric stations and reservoirs. Near Perm, on the river Kama, the Kamskaya  Hydro  was constructed in 1954. On the dam foundation, under argillites, sandstones, gypsum limestones  and dolomites  of  the  Ufimian  stage,  there  occur  gypsums  and anhydrites of the Kungurian stage which are regional waterproofs. After  filling the  reservoir filtration was intensified at the dam foundation. In  some  parts sulphate  waters  appears  which indicates the dissolution of  gypsum.  In  this situation, consolidation of the existing cement curtain was done with a chemical gelforming  silicate  solution. The injection consolidation  and  post-injection processes  provided  gypsum  protection against dissolution  and  increased  the stability of the dam.

Filling  the  Kamskoye reservoir raised the water level by 20  to  22m.  Its banks  within the limits of the Krasnokamsk-Polazna swell are laid with  gypsums and anhydrite  of the Kungurian stage. Part of the caves was inundated.  In  the waves impact  zone  there  formed  leaching  processes  and  new  small  caves. Introduction  of  the  river  waters  into  the  karstified   rocks,   seasonal fluctuations of  the water level in the shore area reaching 7 to  8  m,  caused activation  of suffosion, removal of material from the filled  karst  cavities, gypsum dissolution and collapse forming. In the reservoir influence zone on  the territory  of  the  settlement Polazna, from 1956 to  1961  there  occured  11 collapses while for the previous 50 years there were only two.

The  karst  activation both in the upper and deep horizons  is  observed  in connection with drilling operations for oil, gas and salt as well as development of oil and potash salts deposits in the same areas. The boreholes are  imperfect which  cause vertical flow exchange and mixing of mineralized and  fresh  waters and  increase the waters aggressivity towards the soluble rock.  Some  abandoned wells  gush polluting the rivers. At present well constructions are improved  to provide the aquifer isolation.

About  50  per  cent  of  oil  resources  is  confined  to  fractural  karst reservoirs. Developing  a greater part of a deposits by fresh  water  injection into  wells  to maintain pressure can activate  the  dissolution  processes  of carbonate  and  sulphate salts in deep horizons. The processes are  promoted  by activity  of  sulphate-reducing bacteria.  To intensify  the  oil  inflow,  the hydrochloric  acid  is  injected into the seam (up to 100 m³ and  more)  at  the concentration of 10 to 20%. As a result of the carbonate rocks dissolution  near the  well,  the  volume of the fractural karst reservoirs and  the  oil  inflows increase. As noted by I.N.Shestov et al, an active impact on karstified rocks in the oil development wells spreads over to the depth of hundreds of meters.

In territories of considerable technogenic load, the conditions and  factors of  karst formation change considerably due to irreversible  transformations  of the  landscape and  the rocks, pollution of  surface  and  underground  waters, atmosphere and atmospheric precipitation, degradation of vegetation.

An  example  is Verchnekamsky industrial complex including,  besides  potash salts enterprises  of  the  city,  settlements,  large  water  intakes,  linear (engineering) constructions,  timber processing and oil  industries.  The  salt extraction has been taking place there for more than 500 years. The salt stratum of the Kungurian stage (underlying rock salt, potash salt, overlying rock  salt) and  the  intermediate  stratum are overlied with  clays,  limestones,  gypsums, marls,sandstones of the Ufimian stage and Quaternary deposits to which  aquifers are confined. In chamber working of potash salts artificial cavities are formed, redistribution of stresses in the rocks takes place, opening of fractures in the overlying  rocks,  slow sinking of the surface. According to  G.V.Beltyukov,  in driving  and developing all the mine shafts in fractural zones there  are  noted waters  shows.  In the overlying rock salt and in the carnallite  rock  in  some places  there  were  uncovered karst cavities of hundreds  of cubic  meters  in volume.  In July 1986 in one of the sites there occured a collapse sink. It  had the size of 40 by 80 m on the plane with the depth of 25 m to the  water level. The collapse was accompanied by a gas explosion and light effect.

In worked-out tunnels there condenses moisture in the form of small pools or drip from the roof. In some sites it dissolves the salt, in others there deposistalactites and sinter salt crusts from oversaturated brines. The salt  leaching zones  formation had been promoted by, in the past, brine extraction from  more than  200  wells  of  salt industry. Some  abandoned  wells  have  turned  into "artificial" springs. In drilling wells of the former salt fields karst cavities were uncovered in the salt strata.

The potash salt industry occupy an area of more than 700 ha. Every year they increase  by several millions of tons. The mine dump and industrial liquid  wast receivers  pollute  the  environment  by salinization  and  create  a  lifeless technogenic landscape. In salt mine dump there develops a peculiar "technogenic" karst  under the effect of atmospheric precipitation and temporary surface  run-off: numerous ponors, karren, small sinkholes, channels and caves.

Various  kinds  of the human economic activities called  technogenic  impact change  karstic  processes course. These changes have various  trends.  In  most cases the technogenic impact lead to activation of karst processes as a  result of  the environment change (rocks, hydrosphere,  atmosphere,  biosphere)  which determine the  basic  conditions  and factors of  karst  formation.  The  karst activation  has a negative impact on engineering geological conditions  and  may cause hazardous situations. It shows itself not only in upper but in much deeper horizons of the rocks. Slowing of the karst process is a result of some or other engineering geological measures connected with construction on karstified rocks. The environmental response to the technogenic impact depends on the karst  type: saline,  sulphate,  carbonate. As a result of mining activities on  the  surface there  accumulate  soluble  technogenic soils which  show  "technogenic  karst". Remove of dissolved components from the soils pollute the environment. The human economic  activities  being  planned  in karst areas  must  be  based  on  the predictions of the karst process in view of the environmental changes under  the influence  of the existing and designing engineering works and providing  nature protection measures.

Michael Price (England)

SUMMARY: The Chalk aquifer of England can be thought of as a  multi-porosity medium. The matrix is a fine-grained limestone which generally has high porosity but small  pore throats, so that its permeability is typically only 0.1 to 10 millidarcys (10^-4to 10^-2 m day^-1).A fairly  uniform  fracture system imparts a secondary permeability, which appears to be about 100 to 1000 mD(0.1 to 1 m day^-1).  Where the chalk forms a major aquifer, most of the transmissivity results  from the enlargement of fractures, by solution,to form a few highly permeable zones. Over much  of  the  outcrop, weathering leads to  the  development  of  shallow permeable  layers  to form an additional component. Each of  these  permeability systems  influences some aspect of subsurface water movement, with  implications for resources, quality and construction.

The  Chalk  of  England is an unusual aquifer in that it  can  have  several superimposed  components  of porosity and permeability, althouth not  all  will necessarily  be present at any one locality .Universally present is a matrix  or intergranular  component;this  can contribute porosities of  more  than  40%,the porosity  generally  being higher in the southern part of England  than  in  the northern part and also increasing up the stratigraphic succession.

The  matrix permeability is generally isotropic and shows the same  regional and  stratigraphical trends as porosity. It is generally low, seldom  exceeding 10mD (about 6´ 10^-3 m day^-1); a hydraulic conductivity value of 10^-3 m day^-1 is more typical.

The second permeability component---termed the primary-fissure  component---is caused  by a fairly ubiquitous fracture system,usually consisting  of  three near-orthogonal  sets of joints. The degree of openness of these  joints  varies from place to place, depending on factors such as tectonic history and how  much solution  has taken place as a result of sub-surface flow. At  depths  much  in excess of 100m, the joints may be effectively closed. The hydraulic conductivity imparted  by  these joints is generally still too low to explain  the  Chalk's performance  as an aquifer;typically it is in the range 10^-2-1  m  day^-1. The  presence   of  the  primary-fissure  and  matrix components  of  porosity   and permeability means that the Chalk is a double-porosity system.

The  primary-fissure  component  of  permeability can  be  enhanced  in  two circumstances  .In  the upper few metres of the chalk at  outcrop  the  fracture openings can become enlarged and the block size reduced, leading  to  hydraulic conductivities greater than 10 m  day^-1 when the material is saturated. Frequently, however, this material  lies  in the unsaturated zone. In the top  few  tens  of metres  of  the aquifer the primary fissures may be enlarged by  solution.  This enlargement typically seems to occur along individual near-horizontal  fractures or  in  discrete  near-horizontal zones,rather  than  uniformly  throughout  the aquifer.  The  non-uniform  permeability so produced is  termed  the  secondary-fissure component. These secondary feasures appear to be related to river-valley base levels, although some may have developed in the geological past.

The  secondary  fissures ,being essentially highly  permeable  layers,impart heterogeneity  to  the Chalk where they are present;thus they  cause  a  double-permeability  behaviour to be superimposed on the double-porosity behaviour. The permeability contrast between the secondary and primary-fissure components is so great, however,that this double-permeability behaviour can be expected to appear as another double-porosity system; the Chalk can thus be a dual  double-porosity aquifer. Some progress has been made in the study of the fissure  permeabilities using packers; this  approach needs to be combined with  some  of  the  latest analytical techniques developed in the oil industry, although in the  unconfined contdition there are likely to be problems in obtaining unique interpretations.

In  the unsaturated zone, matrix flow appears to be dominant throughout  the year at some sites, with pore-water suctions nearly always too high for flow  to occur  in fissures. At other sites there is evidence that fissure  flow  occurs after  heavy rainfall.Good  agreement is  seen  between  unsaturated  hydraulic conductivity curves measured  in  situ  and  predictions based  on   pore-size measurements and calculated fissure openings.

The small pores in chalks mean that the matrix has low permeability  despite its high porosity. Most of these small pores do not drain under gravity, so that the specific yield of chalk is low; however,much of the pore water is accessible to plants.

In the confined condition, an example fom Norfolk suggests that most of  the water  released from elastic storage is derived from closure of  fissures.  Some water  will be released by expansion of pore water from the matrix;some  of  the elastic storage may take a finite time to become apparent and may be erroneously interpreted in pumping test analyses as leakage from adjacent strata.

The  variability of the permeability components throughout the Chalk  is  so great that   exceptions   will  be  found  to   almost   any   generalization. However,generalizations  can be valuable from the practical point of  view.  The Chalk is England's major aquifer and its unusual properties have  an  important influence  on the  supply  of water and  its  susceptibility  to  pollution.  A knowledge  of  the properties and flow mechanisms of the  unsaturated  zone  is essential to an understanding of the risk of pollution to the groundwater of the saturated  zone. In the saturated zone the secondary fissures are  the  pathways for  most  groundwater movement,  and the smaller  but  more  numerous  primary fissures  and the matrix pores contribute storage. Because of the extensive  and permeable  secondary-fissure systems  in  the  upper  part  of  the   saturated zone,water   can  travel  large  distances with  great  rapidity,meaning   that pollutants  can be quickly and widely dispersed; the high matrix porosity  means that pollutants can diffuse into the matrix so that they may be greatly  diluted but  may  also  remain  there for long periods. It is  hoped  that  the general comments in this paper will have provided some insight into the behaviour of the chalk aquifer.

P.E.LaMoreaux (USA)

The  sudden  formation of sinkholes or "catastrophic subsidence"  in  recent years has focused attention on a little-understood geologic hazard. Few  people realize  that thousands  have formed in the United States  since  1950.  Costly damage, some accompanied by injuries and loss of life, has resulted from  sudden collapses  beneath highways, railroads, bridges, buildings,  dams,  reservoirs, pipelines,   vehicles,  and drilling  operations.  Perhaps  one  of  the   most spectacular was the "Golly Hole" collapse on December 2, 1972, in Shelby County, Alabama;  another  was the surface collapse of part of a city  block  in  Winter Park, Florida, in 1981.

Sinkholes  can  be  separated  into categories defined  as  "induced  "  and "natural." Induced  sinkholes  are  those  caused  or  accelerated  by   human activities,  whereas natural  ones  occur in  nature.  Recognition  of  induced sinkholes or catastrophic subsidence, and their investigation has been confined mainly  to  this  century. Almost all  investigations  dealing  with  triggering mechanisms or processes have been made since 1950.

The purpose of this article is to describe techniques used in a case history to relocate a gas pipeline in a highly vulnerable karst setting.

Active  subsidence (catastropic  collapse) in  Dry  Valley,  Shelby  county, Alabama,  USA,  presented  a danger to  highways,  railroads,  buried  telephone cables,  personal propetry, farm animals, and oil and gas pipelines,  including the Southern  Natural Gas 10-inch Bessemer to Calera pipeline.  Many  collapses have occurred  along  the  pipeline  right-of-way.  Some  collapses   directly underneath the pipeline exposed it.

Geologic, geophysical, and hydrologic surveys along the pipeline  identified the  areas  where sinkholes could occur. Extensive collapse  sinkholes  resulted from a combination of factors, including groundwater withdrawal, modification of surface drainage,  construction  activities,  and  heavy  and  prolonged  rain. Catastrophic collapse  in  the  area will  continue  indefinitely  until  these conditions change. Therefore, an alternative pipeline route had to be chosen  to anchor the pipeline to bedrock with anchor points not greater than 20 feet apart because of the strength of the pipe.

Determining  the  geographic  distribution, frequency,  and  probability  of catastrophic sinkhole occurrence was accomplished by the following works:

1.  Preparation  of a detailed map of the geology and  structure  along  the pipeline in the critical areas of subsidence.

2.  Mapping of exposures of bedrock limestone in quarries,  road  cuts,  and sinkholes  to determine dip and strike of bedding and joint and fault trends  to relate to preferential solution zones and groundwater flow patterns.

3. Acquisition and analysis of satellite imagery and high- and  low-altitude aerial photography (black and white, black and white infrared, color  infrared, color). Resulting regional and local geological structural trends,  lineaments, and  sinkhole and  drainage alignments were  studied  to  project  preferential groundwater flow patterns and solution zones in bedrock limestone.

4. Use of seismic geophysical studies and test drilling to define the top of bedrock and overburden thickness along the alternate pipeline route.

5.   Determination   of  geology  along  the  new  pipeline   route   before construction,  which  was verified during its construction to  ensure  that  the pipeline was securely connected to bedrock.

6.  Monitoring of sinkhole-subsidence occurrence on a monthly basis  over  a period of 38 months. Each month, photography from an overflight was analyzed and subsidence features located were checked in the field and documented.

Based on the various studies, two alternate pipeline routes were  delineated that would reduce the danger from catastrophic subsidence beneath the  pipeline. Alternate route 1, the final route chosen, was the best and most  direct  route across Dry Valley. It followed shallower bedrock, had less overburden thickness, fewer  sinkholes,  and undisturbed drainage, and crossed an  area  underlain  by less limestone and a larger area underlain by Athens Shale.

Construction  for  the new pipeline route involved opening  the  ditch  line twice.  The ditch was first dug to remove all bedrock float and  pinnacles.  The ditch was backfilled and dressed at the end of each day to prevent rainfall  and surface  runoff from entering. During excavation, it was noted that bedrock  was shallower  and pinnacles were more frequent beneath Dry Valley  than  previously identified. Construction  was redesigned to obtain maximum bedrock  support  to pipeline.

The  ditch  was  then reopened to lay pipe.  Fractured  bedrock  zones  were grouted, where  necessary. Supports of steel piling driven to  bedrock  with  a crossbar  were erected  in areas of deep unconsolidated  overburden  and  large solution  features.  A steel casing was placed beneath a  railroad  and  Shelby County Highway 16 to protect the pipeline from excessive weight. These  supports were tied directly to bedrock.

The new pipeline was cleaned, tested, and tied into the old pipeline. Valves were placed on both the old and the new pipelines so that the old line could  be reactivated if  necessary. The original pipeline across Dry Valley  was  purged with nitrogen.

Tree roots and logs were removed from the overburden and a clay lining   was placed  in  high  subsidence  risk areas adjacent to  the  pipeline  to  prevent downward migration of water into the ditch. After the pipe was laid, the  ditch was  backfilled and a clay crown was spread over it. The right-of-way  was  then graded  and restored to approximate original land surface. It was then  properly terraced  to  control  surface drainage, seeded with  grass,  and  fall  fences previously crossing it were replaced. Natural drainage was left unobstructed.

Subsequently, the right-of-way has been monitored through a period of  rains during which catastrophic subsidence might be expected. No subsidence has  been recorded to date along the right-of-way and the area is now completely reclaimed and vegetation recovered.

Photo 10. Yakaciflic Sinkhole in Alvan Polje, Turkey(Painting by Wang Keda

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