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DR.C.P.LoUniversity of Georgia
Athens, GA 30602
Photographic Analysis of WaterQuality ChangesChanges in water quality in the Rambler Channel of HongKong were analyzed using aerial photography taken in 1956and 1975.
INTRODUCTION
POLLUTION OF THE environment is a universal problem which accompanies
growth and urban development. In the smallbut over-crowded city of Hong Kong, theproblem is even more acute with the lack ofspace for expansion as a result of its inherenttopographical restrictions. Coastal reclamations have been the solution ever since 1841when this British Colony was established. Onthe land acquired from the sea spring up the
scale reclamation project has and is still beingundertaken by the Government along thesurrounding coastal areas.
METHOD OF ANALYSIS
The use of aerial photographs has beenfound to be the most efficient way of detecting the sources of water pollution and mapping the outfall patterns in the sea(Strandberg, 1964, 1966; Scherz, Graff andBoyle, 1969; James and Burgess, 1970;
ABSTRACT: Black-and-white aerial photography for 1956 and true-coloraerial transparencies for 1975 at 1:10,000 scale are used to study theimpact of a changing environment on the water quality of RamblerChannel in Hong Kong. The extensive reclamation in the area undertaken by the Government has significantly transformed the land useof the coastal areas and inevitably has led to man-made pollution ofthe sea water. The aerial photography has been found to be an efficient tool in detecting sources ofpollution and in identifying the typesof polluting substances, especially with the aid of the true-colortransparencies. All these are shown on two maps prepared directlyfrom the aerial photographs with the aid of a Zoom Transfer Scope.
commercial center, factories, and housing estates. This type of coastal reclamation is usually on a very large scale and has inevitablycaused great changes to the natural environment. The most notable effect of these is thepollution of the sea water within the harborarea of Hong Kong. In order to examine moreprecisely the impact of these environmentalchanges on the coastal waters, the RamblerChannel area, which is located to the northwest of Kowloon Peninsula just outside themain urban residential belt, is selected forstudy (Figure 1). This Channel is formed between the Tsing Yi Island in the west and theKwai Chung district on the mainland in theeast. It is ideal for this study because a large-
Welch, 1971). By comparing results of photographic analyses of the same area at twoperiods of time, the impact of a changing environment on the water quality of the harborcan be evaluated. Fortunately, old aerialphotographic coverage of the Rambler Channel area is available. These are "splitvertical" aerial photographs taken by theBritish Royal Air Force on December 27,1956 with a reconnaissance camera (focallength = 50.8 em) at a height of 5090 m, thusgiving a nominal scale of 1: 10,020. The timeof photography is not known but its absenceof shadows indicates that it must have beenobtained near noon. They are good qualitycontact paper prints and admirably serve the
PHOTOGRAMMETRIC ENGINEERING AND REMOTE SENSING,
Vol. 42, No.3, March 1976, pp. 309-315.309
310 PHOTOGRAMMETRIC ENGINEERI G & REMOTE SENSI G,1976
FIG. 1. Location of the study area.
purpose as a standard datum for comparisonwith later changes. The up-to-date photography of the area was specially taken by theFlying Unit of the Crown Lands and SurveyOffice, Public Works Department, for theDepartment of Geography and Geology,University of Hong Kong on January 5, 1975at 10:25 a.m., using a Wild RC-lO camera(focal length = 152.53 mm) at a height of 1524m, thus giving a nominal scale of 1: 10,000.The film employed is true-color Kodak Ektachrome Type 2448 processed to reversaltransparencies for use in the analysis of water
quality. Black-and-white contact prints alsoare made from these color positives to aid inthe analysis. Thus, the two photographiccoverages of the area are compatible in time,and a detailed comparison of the environment changes in 19 years' time in the area isfeasible. Basically, the procedures involveinterpretation of the land use in the area andmapping of the sources of water pollutionfrom aerial photographs with the mirrorstereoscopes. A working definition for waterpollution employed is that given byStrandberg (1964): "the adding to water ofany substance, or the changing of water'sphysical characteristics in any way which interferes with its use for any legitimate purpose." In addition, the different types ofwater-polluting substances can be identifiedmore specifically. The Bausch and LombZoom Transfer Scope has been employed tomap the land use and outfalls in the sea fromthe aerial photographs at a common scale of1:10,000.
CHANGING ENVIRONMENTAL
CHARACTERISTICS
The results ofthe photographic analysis areshown in the two maps, Figure 2 and Figure3, respectively for 1956 and 1975. The following environmental changes can be noted:
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FIG. 2. Land use and water quality in Rambler Channel 1956 as interpreted from theaerial photographs.
PHOTOGRAPHIC ANALYSTS OF WATER QUALITY CHA GES 311
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FIG. 3. Land use and water quality in Rambler Channel 1975 as interpreted from the aerialphotographs.
RECLAMATION
The most dramatic change which has takenplace in this area has been the modificationsof the shorelines by reclamation. In 1956,Tsing Yi Island was still relatively free ofreclamation. Only some minor strips aroundthe Tsing Yi Bay area have been reclaimed.However, a large-scale reclamation had juststarted in the Lap Sap Wan (literally, "Garbage Bay") area on Kwai Chung mainland.This is indicated by the extensive plumes ofsediment (labelled "A" in Figure 4) movedby currents towards the eastern coast. Thename of the bay signifies that waste materialshave been dumped as a means of garbagedisposal and for reclamation. However, thebays and inlets in this area can still be delineated from the aerial photographs. By1975, the reclamation has already covered upall these bays and inlets ("B" in Figure 5),while excavation of the hillsides has beencarried out in order to provide the materialsfor filling up the bays ("C" in Figure 5). Similarly, on the shoreline ofTsing Yi Island, theT6ing Yi Bay has been so filled up that afootbridge can be constructed to link up themouth of the bay, while excavation for therequired filling materials has been carriedout on the hillslopes adjacent to the newbridge (See also "0" in Figures 6 and 7). Theeffect of reclamation is to eliminate all indentations along the shorelines. However, in
order to provide adequate shelters for fishingboats andjunks in this area, artificial sea wallshave been constructed to enclose zones ofquiet water along the newly formedcoastline: one between Nga Ying Chau andNorth-east Tsing Yi Island, and one along theKwai Chung coast on the mainland ("E" and"F" respectively in Figure 7).
FIG. 4. An aerial photograph of Lap Sap Wanarea in 1956.
312 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1976
FIG. 5. An aerial photograph of Lap Sap Wan area in 1975.
LAND USE
In 1956 the surrounding coastal areas ofRambIer Channel revealed a basically ruraleconomy with the occurrence of crop landalong the river valleys and on alluvial patchesalong river estuaries. Paddy rice, a cropshowing a distinctively elongated field pattern and a fallow texture at the time of photography (the season being winter), was important in Tsing Yi Island which was then quiteisolated from the mainland market ("G" inFigure 6). Intensive vegetable cultivation,being distinguished by the smaller plot sizeand dark texture of the leaves, also was practiced to a lesser extent on Tsing Yi Island butmore importantly on the Kwai Chung mainland ("H" in Figure 4). Industrial activitieswere only of a small scale associated with theagricultural economy; the most importantwas the oil storage depot on an artificiallyreclaimed strip in Northern Kwai Chungcoast. A noteworthy use of land is the cemetery ("J" in Figure 4) which covered only asmall hilly area just above the oil storage depot. Another significant aspect was the extensive occurrence of gully erosion forming badland, especially on the hill areas of the KwaiChung mainland (e.g., "K" in Figure 4).
By 1975 a very different land use pictureemerges. Agriculture has declined, espe-
cially on the Kwai Chung mainland area,while on Tsing Yi Island, vegetable cultivation has become more predominant overpaddy rice (e.g., "L" in Figure 7). More extensive areas of trees are found on Tsing YiIsland, reflecting an effort to check soil erosion, but on the other hand devastation of
FIG. 6. An aerial photograph ofTsing Yi coastin 1956.
PHOTOGRAPHIC ANALYSTS OF WATER QUALITY CHANGES
FIG. 7. An aerial photograph ofTsing Yi coast in 1975.
313
these trees by fires is quite common as shownin Figure 3. Large-scale industrial activitieshave been established, for example, the addition ofa new oil storage depot on the island of
ga Ying Chua ("M" in Figure 7); theemergence of an iron scrap-machine fabrication factory ("N"), a cement factory ("0");and a dyeing factory ("P"), all along the eastern shoreline of Tsing Yi Island (Figure 7).These have resulted in the growth ofthe TsingYi Town situated on Tsing Yi Bay. The mostimportant development in the area has beenthe establishment of a modern container terminal complex on the reclaimed land ofKwaiChung coast ("B" in Figure 5). This terminaleventually will assume an important role asthe outport of Hong Kong, and will necessitate the development of a new transport system, including the construction of a bridge("Q" in Figure 7) linking up Tsing Yi Islandwith the Kwai Chung mainland and multilevel highway connections with the urbanareas in the south-east; both are very vividlydisplayed in the aerial photographs. Finally,as an indication of growth, the cemetery hasbeen greatly expanded since 1956 to includethe other half of the hill in the north ("R" inFigure 7).
IMPACTS ON WATER QUALITY
The drastic modification of the shoreline
and the establishment of new types of landuse have affected significantly the waterquality of the area in several ways.
TURBULENCE AND TURBIDITY
A more narrow channel resulting from reclamation has increased the turbulence of thesea water as revealed by comparing the toneof the sea water registered on the aerialphotographs at the two different dates. Thestrikingly uniform dark tone as exhibited bythe water in the 1956 photography (Figures 4and 6) contrasts with the much lighter anddiffused tone of the water in the 1975 photography (black-and-white contact prints fromtrue-color transparencies) (Figures 5 and 7).This indicates a greater degree of turbidity ofthe sea water in the Channel in 1975. Oneother factor of increased turbidity may be thegreater number ofvessels plying this channelin 1975 (as indicated by the presence of shelters and a large number of junks moving andanchoring in the area) than in 1956 (See Figures 6 and 7).
SOURCES AND TYPES OF POLLUTION
From the aerial photographs, the sources ofpollution can be detected readily throughtonal contrast. In 1956 one can detect eightmajor sources of pollution as marked on Figure 2. These are invariably located at the
314 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1976
river estuaries. The most seriously affectedarea is Lap Sap Wan (Garbage Bay) in theKwai Chung mainland where three plumes ofsediments (marked numbers 1, 2 and 3 onFigure 2; also see Figure 4) converge into thebay. The dark-colored and rough-texturedplume in Figure 2 is indicative ofthe washingdown ofwaste materials and garbage from thevillages and farm land in the upper course ofthe stream. Deltas are under construction at 2and 3 in Figure 4.
The high rate of sedimentation here is associated with soil erosion as indicated by theprevalence of gullies in the vicinity. Alongthe Tsing Yi Island shoreline, two majorsedimentation areas are noted (marked asnumbers 4 and 5 on Figure 2), leading to theformation of marshes. The most extensivepiece of marshland so formed is at the head ofTsing Yi Bay (marked number 4 on Figure 2).The different stages of sedimentation areclearly revealed with the very fine and darkermuddy sediments being deposited nearestthe sea. An initial stage ofreclamation can beseen with an earth-dam being built across thebay ("D" in Figure 6). The sedimentation onTsing Yi coast is less severe than that on theKwai Chung coast as a result of the moreluxuriant vegetative cover and hence bettersoil conservation. The presence of the oilstorage depot has not given rise to any signs ofwater pollution. It is noteworthy that reclamation work at the Lap Sap Wan area hascaused plumes of dumped materials (markedas number 8 on Figure 2 and "A" on Figure 4)to be moved by currents across the mouth ofthe bay. In this way the work of reclamation isspeeded up.
The employment of Ektachrome true-colorreversal transparencies for 1975 has facilitated the detection of the polluting sourcesand particularly the identification of thetypes of polluting substances in the area. Inall there are ten major sources of pollutionwhich have been marked with a number onFigure 3 and the appropriate photographs. Itis noteworthy that eight of these have beencaused by men in the most direct way, whileonly two may be considered to be the result ofsedimentation. The first three sources alloccur within the artificially built boat shelterarea ("F" in Figure 7) and are caused by discharges of underground sewerage drains.The most serious sewer source is marked 2 onFigure 3 and Figure 7 and gives out a longblack plume of water. This sewer drain pollutes the sea water within the shelter area andrenders the color of water much darker greenthan that outside. While the shelter may acttemporarily to block out the polluting water
from the open sea, the seepage ofthe pollutedwater through an outlet marked A on Figure 3is evident from the photograph (Figure 7).
The fourth source is iron stain coming outfrom the new iron pipes being installed asunderground drains for the reclaimed land.The fifth source is pollution by the muddymaterials used for reclamation on the coast.At number 6 on Figure 3, pollution of thewater occurs between the newly establishedcontainer terminal and the mainland coast.This is likely caused by oil residues left byboats and junks in this more sheltered area(Figure 5). Along the Tsing Yi shoreline, themost seriously polluted spot is the bay atnumber 7 marked on Figure 3. This bay isdangerously polluted by chemical wastes associated with the nearby dyeing factory. Thecolor transparency reveals light bluishplumes and dark grey sediments (Figure 7) inthe bay. Just opposite is the new boat shelterformed between this bay and Nga Ying Chauwhere a new oil storage depot is found. Agreat number of boats and junks has beenattracted to berth inside the shelter. The situation is worsened by the presence of boatbuilding shacks along this strip of the coast ofTsing Yi Island (Figure 7). The area betweenthe two oil storage depots has revealed a largepatch and dark-toned water (marked asnumber 8 on Figure 3 and Figure 7) which ismoved towards the Channel by the speedboat. This is most likely oil polluted.
Another source ofpollution is the extensivemarshland ofTsing Yi Bay, noted in the 1956photographs, which has by now been partlyreclaimed (marked as numbers 9 and 10 inFigures 3 and 7) with the establishment of alarge machine fabrication factory and somewarehouses at the footbridge crossing. Thesehave led to the growth of a stilted-house settlement and boat-anchoring places aroundthe factories. All these have contributed towards the pollution ofthe sea water, althoughsedimentation is still an important cause.
WATER MOVEMENTS
By examining the direction ofmovement ofthe plumes of discharged sediments, it hasbeen possible to map the movements ofwaterin the Rambler Channel as shown in Figures2 and 3. It is clear that a south-to-northmovement was dominant in 1956, but by 1975with the construction of boat shelters and reclamation a less regular movement of the seawater is noted. Although the predominantsouth-to-north movement still can be discerned, there is also a great amount of westto-east movement between Tsing Yi Islandand Kwai Chung mainland. Because the
PHOTOGRAPHIC ANALYSTS OF WATER QUALITY CHANGES 315
inner harbor area of Hong Kong is located tothe south-east of Rambler Channel, 'thesouth-to-north movement is beneficial; thepolluted water is diverted away from themore densely built-up inner harbor area.With the evidence interpreted from the aerialphotographs, the reclamation appears to haveaffected the direction of movements of thesea water.
CONCLUSIONS
The aerial photographic analysis undertaken has succeeded in revealing in a mostdramatic manner the effects of a changingshoreline on the pollution of the sea water inRambler Channel. It is clear that the reclamation, with its accompanied urbanization ofthe rural areas, has brought about land-usechanges from extensive cultivation to intensive, market-oriente:I cultivation and fromagricultural to industrial. These changeshave brought about pollution especially inthe bays and inlets where reclamation takesplace and where factories are set up. Landreclamation is obviously important to theeconomy of Hong Kong, particularly as witnessed by the establishment of the new container terminal. It is perhaps fortunate in thisarea that the seriously polluted sites are usually in confined locations and are less accessible to the open sea. Immediate measures,however, should be taken by the Government to clear up these seriously polluted sitesas pin-pointed by the aerial photographs.
This study has supported the usefulness ofaerial photographs in detecting the sources ofpollution in the sea water. Color photographyin the form of transparencies as employed inthis study allows easy detection of dischargepoints along the shorelines and identificationof the nature of the polluting substance. Onegreat advantage of the aerial photography is
emphasized in this study; its ability to freezea scene of the environment at a specific timeand, by comparing scenes at different times,all the changes can be revealed. The availability of simple mapping instruments such asthe Zoom Transfer Scope has facilitated themapping of the sediment plumes in the sea,thus speeding up the exploratory study ofwater pollution.
ACKNOWLEDGMENTS
The author wishes to acknowledge the financial support of the Higher Degree andResearch Grant Committee, University ofHong Kong, which makes possible the colorphotography to be taken over the RamblerChannel. He is grateful to the Crown Landsand Survey Office, Public Works Departmentin Hong Kong, for carrying out the photography. Doctors R. Welch and C. Pannell ofthe Department of Geography, University ofGeorgia, have made useful comments on anearly draft of this paper. To both of them theauthor's thanks are also due.
REFERENCES
1. James, W. and Burgess, F. J., 1970: "OceanOutfall Dispersion," Photogrammetric engineering, Vol. 36, pp. 1241-1250.
2. Scherz, J. P., GrafT, D. R., and Boyle, W. C.,1969: "Photographic Characteristics of WaterPollution," Photogrammetric Engineering,Vol. 35, pp. 38-42.
3. Strandberg, C. H., 1964: "An Aerial WaterQuality Reconnaissance System," Photogrammetric Engineering, Vol. 30, pp. 46-54.
4. , 1966: "Water Quality Analysis,"Photogrammetric Engineering, Vol. 32, pp.234-248.
5. Welch, R., 1971: "Remote Sensing for WaterPollution Control," Photogrammetric Engineering, Vol. 37, pp. 1285-1286.
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