Drainage Master Planning For Land Drainage ·Flood Control .
6Drainage Master Planning forLand Drainage ·Flood Control inthe Northern New Territories ofHong KongKen K C LukBSc(Hons) MEngSc PhDMHKle MIEAustMaunseU ConsultantsAsia LldAlex K F Kwan8Sc(Hons) MScMHKIEMaunsell ConsultalltsAsia ltdJohn K Y L.ungBSc(Hons) MSc(CPM)MEngSc MHKIE MIEAuslDrainage ServicesDepartmentSince the establishment of the Drainage Services Department in 1989, strategic studieshave been carried out to develop a comprehensive land drainage and flood controlstrategy to prevent flooding and provide necessary drainage infrastructure for Futureneeds. AFter Formulation of the land drainage and Flood control strategy, sevenDrainage Master Plan studies have been and are being carried out on different drainagebasins to resolve the drainage issues according to their drainage characteristics anddevelopment pressures. This paper discusses the Drainage Master Plan Study in theNorthern New Territories (NN T DMP Study) as a case study to illustrate theconsiderations taken in Formulating the strategy to handle one of the most flood proneareas in Hong Kong.The NNT is susceptible to serious and Frequent floodings due to its low-lyingtopography and inadequacies in the drainage system. Yet, the area is subject to highdevelopment pressure due to enormous population growth and urban expansion . Inorder to alleviate flooding and to support sustainable growth of the area, the NNT DMPStudy has carried out comprehensive hydrological and hydraulic modelling based on areview of development trends in the area. With the support of the modelling results,various structural and management measures have been devised to resolve the drainageproblems. Particular attention is drawn to the residual Flooding problems and therecommended solutions.Keywords: Drainage Master Plan, Flooding, Prevention, DIA, AIMSINTRODUCTIONco mprehensive and long-te rm so lut io n to the drainageproblems.Due to its geographic location, Hong Kong experiences heavy,yet uneven distribution of rainfall every year. The rainfall in HongKong ave rages 2200 mm annually, and more than 80% of thisfalls during the period May to September. Intensities can be high,with SO mm per hour and 200 mm in 24 hours being notunco mm o n. Flooding in low-lying areas, in particular theNorthern NewTerritories, is therefore frequent. Flood ing can causehuge disruption to transport, communicat ion s, daily life and commercial ac ti vities, inflict fatalities an d damage properties and theeconomy.The impact of flooding becomes more promin ent as theNorthern New Terr itori es has experienced particularl y rapideco nom ic an d housing developm ents over th e la st decade.Development has mu shroomed along major transport networkall over the Northern New Territories. The increase in populationand housing demand has ca ll ed for the provision of facilities andinfras tructure to accommo a te the people an d to sustain theeconomic and population growth.In the past, the prov isi on of drainage infrast ru cture has beenSince the establishment of the Drainage Services Depart-ment (05 0) in 1989, the need to put dra inage a nd flood controlon a rational and planned basis was recogni zed. Over the years,DSD has commissioned consultants to develop a comprehensiveflood prevention strategy for the whole territory. The ultimate goalof the flood prevention strategy is to improve the quality of lifeby alleviating the impact of flooding and reducing the correspondingdamage. The impact of flooding on existi ng developed areas canbe reduced through mitigation meas ures, while the flood risk indeveloping areas can be contained by effective planning andprovision of adequate drainage infrastructure.The Territorial Land Drainage and Flood Control StrategyStudy - Phase I (TE L I) 11 J paved the way and estab lished an over-a ll flood prevention strategy in 1990. Th e strategy ca n be groupedinto five main categories: New flood prevention standa rds Long term structural measures Short term improvement measu resindividua l new towns or parcels of land development. Th is Land use management and legis lative measuresapp roa c h ha s drawbacks o f being unable to formu late a Planned preventive ap proach to maintenancefragm e nted a nd was provided basically to meet the need of
7Following TEL I, DSD commi ssioned cons ultants to ca rriedou-t a Phase II study (TEl 11) 12) to give a more in-depth study onfive flood prone areas in the Northern and Northwest New Territories. During its study period between 1990 and 1993, the TE lltstudy developed computer models and basin management plan sfor the Ganges, Indus, San Tin, Ka m Tin and Tin Shui Wai basins.The TEL 11 study included future land use projections within eachbasin and recommended necessary primary drainage to be co nstructed to mitigate widespread flooding.W ith formulation of the overall flood control strategy andthe implementation of th e recommended primary drainage netwo rks in the Northern and Northwest New Terri tories, DSD hasextended the scope of study. In 1996, DSD employed co nsultants to ca rry out seven Stormwater Dra inage Master Pl an Studies{DMP Studies} to review the performance and condition of theexisting drainage sys tems for most fl ood prone areas over HongKong. The objective of the studi es is to identify inadequacies inthe drainage system and recommend improvement measures.Another important role is to develop a computerised system toenhance the effic iency of drainage asset management by meansof a territory-wide digital database of the drainage network.Pres ented in th is paper are the autho rs' experi ence andinvolvement in the development of the DMP Study on one of themost flood pron e areas in Hong Kong, namely the DrainageMaster Plan Study in the Northern New Territori es.FLOODING IN THE NNTIn the NNT, the San Tin, Indus and Ga nges drainage bas ins makeup an area of approximately 115 km 2 and are subsidiary basinsof the Shenzhen drai nage bas in that covers an area of about 350km 2 . Th e low-lying areas in the NNT are susceptible to seri ousand frequent flood ing. As most of the area in the NNT is a naturalflood pl ain, flooding is a major issue and jeopardi zes some ofthe development potential. Typica l areas subject to flooding i nelude the San Tin floodplai n located to th e north of Castle PeakRoad, the River Beas and River Indus floodplains bisected by theKC RC railway line at Sheung Shu i, and th e Ganges floodp lainnear Kan Tau Wai. Figure 1 shows a typical scene of flooding inNNT. Flat and low lying topographyLocal co nstricti o ns due to inadequac ies in th e drainagesystemIncrease in surface runoff and loss in flood storage due to landuse changes from cultivated o r fallow use to industri al, commerc ial or residential developmentsReduction in conveyance capacities due to increased siltationoriginated from erosion of upland regions, or inadequate controlduring constru ct ionDespite the flooding problem, the pressure of deve lopmentneed remains high. Several Strategic Growth Areas (SG As) havebeen identified in the Pl anning and Development Studies on NorthEast New Territories (N ENn and North West New Territories (NWNncu rrentl y undertaken by the Planning Department and the Terri to ries Development Department to accommodate future population growth and housin g demand. Apart from these SGAs, thereare numerous applica tion s for changes of land use. Fragmentedand indiv idual developments are also taki ng place in the NNT.THE NNT DMP STUDYMajor River Training WorksTo alleviate the floodi ng prob le ms and provide drainageinfrastructure for future development, the Government is implementing a series of major river traini ng works in N NT, followingthe recommendat io ns i n the TEl I and TEl II studi es. Thees timated cost of these major river tra ining works amounts toabout 2.5 billion dollars. After th eir completion, the extent ofregional flooding under design and actual co nditions w ill be greatlyred uced .However, the fl ooding and drainage problems cannot be totallyelim inated and further works have to be ca rried out for thesecondary an d local drainage networks to allevia te local flooding and cater for new developments. In addition, measures haveto be devised to so lve the drainage problems in some low lyingareas which ca nnot be drained by gravity into the primarydrainage channels.Flood Prevention and Drainage Provision in NNT DMP StudyThe primary objective of the ,' NT DMP Study is to identify andrecti fy the inadequacies in the secondary and local drainagesystems to ensu re that th e stormwater runo ff ca n be effectivel yco llected and conveyed into the primary channels.A thorough di scuss ion on flood loss prevention andmanagement is g ive n i n the M anua l and G uidelin es fo rComprehensive Flood Loss Prevention and Management (Ref. 3).Based on the guide lines given in the manual , the DMP isdeveloped accordin g to the foll owing distinct but interconnectedsteps: Identificat ion of NeedsAssessment of Needs and Formulation of DMP Opti onsIdentification of ConstraintsEvaluation of DMP OptionsFormul ation of DMP RecommendationsIdentification of NeedsFigure 1 - Flooding in the Indus Basin of the Northern New TerritoriesTh e main ca use of flooding is generally heavy rai nfallcoupled with high tide. The serious and frequent flooding problems in the NNT are further aggravated by the fo llowing factors :In order to identify the areas where drainage improvement isrequired and to evaluate the adequacy of the drainage systemunder existing and future conditions, both the existing and plannedland use scenarios are considered in details du ri ng the analysisand planning of the drai nage fac ilities for the NNT.
8The planned land use scenario includes the planned developments under the relevant Outline Zoning Plans (OZPs) and theproposed Type A Strategic Growth Areas (SGAs) recommendedunder the NENT and NWNT Planning and Development Studies.The planned land use is assumed to be fully implemented by2011. A hypothetical test condition on ultimate land use, whichassumes that full development has taken place in all developableareas on the downhill side of the break of slope of the NNT studycatchment, is also included.Major flooding areas corresponding to the 1 in 50 year floodare identified through the assessment and drainage improvementmeasures are recommended in the NNT DMP Study. The 1 in 50year flood is used because it is the flood protection standard adoptedby the DSD for main rural catchment drainage channels.Assessment of Problems and Formulation of DMP Optionscult. In many cases, compensation will be made to the affectedland owners; but problems are often more complicated and cannot be solved by simple monetary means. In rural areas, thereare other constraints such as graves, urns and "fung shui" areas.The proposed drainage works should, wherever possible, avoidencroaching, upon these areas.Environmental impacts are also of major concerns. On theone hand, flood mitigation works would alleviate some adverseenvironmental impacts due to flooding, such as erosion ofchannels and damage to agricultural land. On the other hand,there could be certain adverse impacts due to dra'inage improvement works, especially during the construction period. Forexample, works within the Wetland Conservation Area of MaiPo, environmental requirements are particularly stringent.Detailed environmental studies and impact assessments arerequired to assess the feasibility of the project and to evaluateappropriate mitigation measures.Mathematical floodplain and river hydraulic models using acomputer software MIKE 11 are developed as part of the DMPStudy to analyze the flooding behaviour in the NNT. The modelsEvaluation of DMP Optionshave been calibrated and verified using real data and are usedThe option evaluation covers a variety of topics including systemhydraulic performance, land requirements, environmental reviews,traffic reviews, geotechnical considerations, operational andmaintenance requirements as well as cost considerations.Investigations are undertaken to find out the most practical andcost-effective method to meet the Government's flood protectionstandard.Some general but essential selection criteria are included inthe selection process. These criteria include:for developing the DMP.The purpose of computer simulation (or design floodanalysis) is to identify deficiencies in the drainage system and torectify them in a systematic approach. The design flood analysiswas carried out for both existing and planned development conditions. The existing condition represents the expected state ofthe catchment and drainage network at the beginning of the 1999wet season. The planned condition includes all committed catchment developments and drainage works. In modelling the futureconditions, the Strategic Growth Areas (SGAs) in INENT and NWNThave been taken into account.The design flood analysis was carried out for a full range offrequency events using a synthetic rainfall profile as recommendedin the DSD Stormwater Drainage Manual. The performance ofthe drainage system has been assessed for a number of returnperiods: 2, 5, 10, 20, 50, 100 and 200 years. For each returnperiod, different combinations of rainfall and tide have beensimulated in accordance with the joint probability analysisrecommended in the DSD Stormwater Drainage Manual.Information provided by the design flood analysis is used inassessing the catchment responses to storms and determining whereto direct the resources. Flooding problems requiring immediateattention are mitigated by first-aid measures while the long-termimprovements will be provided through project items under theDMP. After identifying the needs, drainage improvement worksare recommended to ensure that the proposed systems will achievethe required flood protection standard.Identification of ConstraintsThe constraints associated with each improvement option are thenidentified and assessed. In formulating the DMP recommendations, due regard is paid to the various constraints and opportunities in order to ensure the proposed improvement works arefeas ib le and cost-effective. Such constraints and opportunitiesinclude land availability, geotechnical considerations, traffic impl ications, environmental considerations, and interfacing roads,drainage or sewerage projects.In general, land ownership and its availability is the mostcritical constraint. Resumption of private land is always a lengthyand time-consuming process. Any proposed land resumption willinevitably create great concerns from the owners and localrepresentatives. With greater development potentials in the NNT,land values increases and this makes land resumption more diffi- Technical difficultiesMajor risksRobustness I ReliabilityMaintenanceImplementation / ProgrammingCapital cost and operation and maintenance costsThe flood control alternatives are evaluated according tothese criteria, with due consideration given to some intangibleelements, such as risk to life and inconvenience to the pub I icdue to flooding.Formulation of DMP RecommendationsA key objective for stormwater management and flood control isto afford a reasonable level of protection against flooding. In otherwords, the potential risk of loss of life and property damage mustbe reduced to an acceptable level. A complete stormwatermanagement policy should encompass both structural and nonstructural measures such that a balanced approach from aspectsof demographic, social, economic, planning, development,environmental impacts, as well as the hydrological and hydraulicphenomena will be undertaken.As the NNT is under a fast pace of development, one of themain emphases of the DMP is to focus on the provision ofadequate stormwater drainage systems to cope with the demandand prevent flooding. The ongoing major river training works inthe primary drainage system is the first step toward this aim. Thenext step is the provision of branch systems to collect andconvey runoff generated from the development areas for safedischarge into the receiving waters through the primary drainagesystem. The major requirements for the future development inthe NNT will therefore focus more on the structural measures,The provision of drainage networks will substantially remove thethreat of flooding and enable development in most areas in theNNT.
9.c::J---Figure 2 - Recommended Drainage Improvement Works for NNTFigure 3 - Residual Flooding Areas in the NNTThe recommended structural measures can be divided intoupgrading of rural channels and replacement of urban drains asshown in Figure 2. They are packaged for implementation in different time frames in order to effectively allocate resources andpublic funds, and to meet the time required for land resumptionand to cope with the constraints identified in various impact assessments.this kind of land use is 2 to 5 years. If residual flooding takesplace on agricultural lands in less severe events, say less than 2year flood events, some flood protection measures will berequired. Otherwise, the area is considered as sustainable foragricultural use and adequate protection level has been provided.In some cases, there are isolated houses or huts scatteredaround the agricultural lands. Residual flooding may affect thesehouses. As such, the number of houses needs to be checked inorder to evaluate the impact of residual flooding.In case development is necessary and flooding cannot betolerated in the area, several alternative management solutionsdiscussed in the following paragraphs may also be adoptedsimultaneously.RESIDUAL FLOODING AND LANDMANAGEMENTDespite the comprehensive structural improvement measuresproposed, some low-lying areas in the NNT will be subject toflooding even after completion of the major river training works.This is due to the fact that some low-lying areas have groundlevels lower than the water level within the future main drainagechannels. As such, stormwater cannot drain into the main drainagechannels by gravity during high floods. This problem is referredto as "residual flooding", but the flooding situation will be to amuch reduced extent jn comparison with the present situationwhere the main drainage works have not been in place.Most areas affected by residual flooding are floodplains ofexisting rivers and the low-lying areas adjacent to the future maindrainage channels. They are mainly agricultural lands withlimited inhabitants. However the extent of area subject toresidual flooding is not small in the NNT, and is shown in Figure3. The severity of the problem varies from one location toanother. A number of alternative approaches have beenconsidered to alleviate the problem depending on its severity andspecific constraints.In the NNT DMP Study, apart from structural measures, thefollowing management (non-structural) options are consideredto alleviate the residual flooding problem: (a) Sustainable landuse planning; (b) Earth filling through coordinated land management;(c) Re-housing; (d) Flood shelter; and (e) Flood relief measures.Sustainable Land Use PlanningFlooding is a major concern only jf people and properties areaffected. It is apparent that land use is a key element in the evaluation of the impact of flooding. In densely residential areas, floodingcannot be tolerated, as risk to life and economic losses are high.Hm. ever, if flooding occurs on marshes, abandoned agriculturalland, the situation can be more tolerable, even flooding occursfrequently.Flooding on actively used agricultural areas, including fish. ponds, is a case worth conSidering. The flood protection level forEarth Filling through Coordinated Land ManagementOne possible way to solve the residual flooding problem is toraise the ground to a level above the river channel bank. Withthis higher formation level, stormwater can drain into the riverchannel by gravity through drainage channels, or undergroundpipelines if provided. This approach can solve the problem effectively without any special maintenance requirements.The reform of land should, however, be carried out in a coordinated manner. Isolated earth filling may aggravate the flooding situation in the adjacent areas. Indeed, the reform of land isnot solely an engineering issue and has to be implemented inconjunction with other programmes such as land and housingdevelopments. The problem is more related to land managementand town planning, and is not confined to drainage engineering.An effective way is to reform the land through large-scaledevelopment projects. For some new town development projects,the whole area is resumed and reformed above the design floodlevel. In so doing, the residual flooding problem will be properlyaddressed.Large-scale developments within the I\ [NT area are beingidentified in the Planning and Development Studies on the NENTand NWNT. Typical examples are the Kwu Tung North SGA andthe Fanling North SGA. Residual flooding problems in theseareas would be reduced significantly if the development areascan be formed above design flood levels.Re-housingFor some isolated houses located in high flood risk areas, such asthe San TIn floodplain, re-housing may be a viable solution. Thiswould minimize the possibility of repeated emergencyevacuations of the villagers by helicopters or boats .
However, re-housing would in volve lengthy admin istrativeprocedures. Also, the local res idents may not accept relocationto a place w here they ca nnot earn a living as used to be. Rehousing may create social impacts and consultation w ith theco ncerned people must be ca rried out prior to formulation of are-housing scheme.Flood ShelterFlood shelters are operated when severe flood ing occurs. Theyserve to protect the l ives of those people affected by flooding.However, the ir properties are inev itabl y subject to the ri sk of flooddamage.To minimi ze the flood risk to people and properti es, the keyis to operate an effecti ve evacuation program, which relies on anaccurate and timely flood warn ing system. The degree of benefitachieved wi ll depend upon the warning time provided to theoccupants in th e residual flooding areas and the ability of theseoccupants to respond.Flood ReliefThe main aim of flood relief is to provide immediate assistanceto overcome personal hardsh ip and distress. including essentialrepairs to houses and the repair or replacement of essen ti al itemsof furnitu re and personal properties.Flood relief ca n be co nsidered as zero premium insura nceand does litt le to reduce the impact of future flood losses.DRAINAGE IMPACT ASSESSMENT AND ASSETINVENTORY MANAGEMENT SYSTEMDrainage Impact Assessment (DIA)It must be borne in mind that even after the comp letion of alldrainage improvement wo rks, includi ng the secondary and localdrainage system proposed under the NNT DMP Study, there wouldbe a need for some assessments on drai nage impacts resulti ngfrom changes in catchment characteristics, such as individual housedevelopments, new cross ings on existi ng chan nels, fi lling onloca l drainage, small sca le changes in land use and interferingwith existing streams, etc.The change in ca tchment characterist ics in NNT willgenerall y have the effects of: (a) increasi ng stormwater runoff; (b)advancing th e time to peak runoff; (c) reducing active floodpl ainstorage; Id) co nstraining floodp lain flow; le) re-d irecting naturaldrai nage during co nstruction; and (f) contributing to soil erosion(and thus downstream siltation ).Careful thou ghts have been given to how the effects of thesedevelopment changes ca n be mitigated. In most cases to date,proper attention has been drawn to the protection of theproposed developments and thei r impacts on other parts of thedrainage basins through a drainage impact assessment (DIAl processdiscussed in TElII Study i n 1993.Th e D IA is a sou nd and established admi nistrative andmanagement procedu re for review ing and controll ing the impactsof developments and public works projects on the drainagesystem and flooding susceptibility. The DIA procedures arecovered in DSD Advice Note No. 1 and DSD Technical Circular18/95 for private developments and public projects respectively.It is recongised in the NNT DMP Study that the control ofrunoff from development depends on the state of the dra inageimprovement works, as well as the pace of development in thestu dy area. When all the drainage improvement works are in place,the constrai nts by drainage on development w ill be reduced. Basedon hydrological and hydraulic modell ing of the drainage basins,interim guidel ines would be developed for DSD to evaluate drainagesubmissions.Asset Inventory Management System (AIMS)To evaluate a DIA submission, a full drai nage system inventoryof the Study area is required. Details of existing and p lanned landuse, and hydrological and hydraulic data are essential. The NNTDMP Study has developed a drainage asset inventory management system (AIMS) which provides a fra mework of the hydraulic behavio ur of the drain age basins and estab lishes a baselineaga inst whi ch the impacts of development on the hydraulicbehaviour of the basin can be assessed.With the Oracle database at its core and Maplnfa as its userinterface, th e A IMS provides an exce llent tool for managementdrainage assets. The system is user-friendly with intuitive wo rking interface to ensure that the users ca n master th e system withminimum amoun t of training.The AIMS is abl e to import existing electro nic data files fo rmanhole and pipe data into the database. It provides appropriatescreen form s for the input of relevant data for all new data of allassets. The AIMS also provides functio ns fo r the users to navigateover base map.The AIMS is able to process query to select se ts of asset dataunder user-defined criteria. The A IMS provides fun ctions tomanipulate and to identi fy, locate, categor ise the selected sets ofasset. It is ab le to display the selected assets or the manipulationresults on screen or as hardcopy of summary tables or drainagemaps. Further, the AIMS provides funct ions to export the selectedasset data in electron ic fil es for use in MicroStation, and also asinput data files for hydraulic modelling software, such as MIKE 11and HydroWorks models.CONCLUSIONSThe land drainage and flood co ntrol issues in the Northe rn NewTerri tories have been dealt with by a comprehensive and effective manner under the NNT DMP Study. The main focus is toprevent flood ing by provid ing adequate drainage infrastructureand effective management too ls to keep track of the dynam icchange of developments and drainage improvements in the NNTdrai nage bas ins.The DMP strategy has been based on the state-of-the-artcomputat iona l hyd rologica l and hydraulic models. The existingdefic iency and future requ irement of the drai nage systems havebeen eva luated and improvement measures have been proposedto pave the way for meeting future demand and preventing flooding. The major requirements for the future development in theNNT call fo r focus more on the structu ral measures. The provi sion of drainage network wi ll substantiall y remove the threat offlooding to most areas in the NNT and enab le development inthe area.Resi dual flooding poses a parti cu lar tech nica l and management challenge in the NNT and forms a major component of theDMP strategy. Various options and measures have been proposedand d iscussed. They can be appl ied to the co ncerned areas tomeet thei r specific co nstra ints and opportun i ties. It must berecognised tha t residu al flooding problem is not solely anengi neering issue and req uires concerted efforts from plann ingand land development management.Apa rt from the proposed secondary and local drainage improvement wo rks w hich amount to an estimated cost of 2 billiondollars, a drainage asset inventory management system (AIMS)has been developed for planni ng and managing the drainage system
11,under the cu rrent and future control of DSD. The A IMS ca n beus d as an anal ytical tool to identify, locate, categorise a nd presentdrainage assets to facilitate checki ng of DIA subm iss io ns. It canalso be used as a management tool for future planning of drainage improvement works.ACKNOWLEDGEMENTThe authors wish to thank the Di rector of Dra inage Servi ces ofthe Government of the Hong Kong Special AdministrativeRegion for permission to publish th is paper. However, the viewsexp ressed are those of th e authors and do not necessa ril y reflectin any way the offi cial v iews on policy of th e Hong Kong Specia lAdministrative Regi on Governmen t.ALEX K F KWANIr A lex Kwan is an Asssociate of MaunsellConsultants Asia ltd and has over 18 yea rs'expe rience in the plan ning and design ofdrainage and sewerage faci lities in Hong Kon gand North America. He was the project managerof Drainage Master Pla n St ud y in theNorthern New Territories fro m 1997 to 1999and was the deputy project manger ofDrai nage Master Plan Study in Tsuen Wan, KwaiChung and Tsi ng Vi from 1996 to 1997 . Hised ucation includes a BSc(Eng) degree in civi l engin eeri ng fromUniversity of Hong Kong and a M Sc degree in environmenta l engineer.ing (with distinction) from Un iveri sty of london, England.REFERENCESIIIMott-MacDonald (1990), "Territorial Land Drainage and Flood ControlStrategy Study Phase I", Report to Drainage Services Departmen t,Hong Kong Govern ment.[2 ] Binnie Maunsell Consultan ts (1993), " Territorial land D rainage andFlood Co ntrol Strategy Study Phase 11", Report to Drainage ServicesDepartment. Hong Kong Government.131 Economic and Social Commission for Asia and the Pacific (1991),"Manual and Guidelines for Comprehensive Flood Loss PrevenUonand Management", United Nations Development Programme.KEN K C LUKIr Or Ken l uk is a Principal Engineer of MaunsellConsultants Asia Ltd . He has over 16 year'sexperi ence in civil engineer i ng wo rks,specializing in flood control and stormwatermanagement. He had wo rked i
Drainage Services Department INTRODUCTION Drainage Master Planning for Land Drainage ·Flood Control in the Northern New Territories of Hong Kong Since the establishment of the Drainage Services Department in 1989, strategic studies have been carried out to develop a comprehensive land drainage and flood control
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