“Pipi Monyet”, Cara Bangkok Bebas Banjir
VIVAnews – Selain berhasil menekan kemacetan dengan pengembangan kereta bawah tanah, Bangkok, Ibukota Thailand, juga telah lama berhasil mengendalikan banjir. Bangkok telah berpengalaman puluhan tahun dalam menghadapi banjir yang menimpa daerahnya.
Warganya tidak lagi perlu takut akan akan adanya banjir parah, karena ibukota Thailand ini mempunyai sistem yang disebut “pipi monyet”.
Pipi monyet adalah sistem penampungan yang terdiri dari 21 wadah penampungan air hujan. Penampungan ini dapat menampung air hujan yang berlebih hingga 30 juta kubik. Lalu pada musim panas, air ini dapat digunakan untuk keperluan konsumsi warga Bangkok, termasuk diantaranya air minum dan air keran.
“Nama ini terinspirasi dari monyet yang biasanya makan berlebih. Kelebihan makanan ini disimpan di pipinya, sehingga pipinya menggembung. Ketika nanti dia merasa lapar, dia akan memakan makanan di pipinya tersebut,” ujar Gubernur Bangkok, Sukhumban Paribatra, yang ditemui usai konferensi pers gubernur dan walikota se-Asia Eropa pada pertemuan Asia Europe Meeting, Jumat, 29 Oktober 2010.
Sebenarnya Bangkok yang terletak satu meter di bawah permukaan laut rawan terkena banjir. Ditambah lagi jika terjadi hujan lebat, gelombang tinggi dari sungai Chao Praya akan meluap hingga ke pusat kota. “Jika hujan lebat datang, aliran air dari utara membanjiri daerah Bangkok,” ujar Paribatra.
Namun, berkat sistem yang telah dikembangkan puluhan tahun lalu oleh kerja keras Raja Thailand, Bhumibol Adulyadej, ketakutan itu sirna. Raja Thailand, kata Paribatra, memiliki pengetahuan dan ketertarikan yang besar terhadap sistem pengairan dan pengendalian banjir di Bangkok. “Beliau menginspirasi sistem ini sehingga dapat bekerja dengan baik,” ujar Paribatra.
Bangkok juga memiliki tanggul sepanjang 72 kilometer dan saluran air sepanjang 75 kilometer untuk mengalirkan air yang meluap dari sungai Chao Phraya. Hal ini, ujar Paribatra, adalah sistem yang telah dikembangkan selama puluhan tahun di Bangkok.
“Sistem pengendalian banjir ini mulai dikembangkan oleh Bangkok setelah kota ini didera banjir parah 27 tahun lalu. Kala itu Bangkok tenggelam selama hampir tiga bulan,” ujar Paribatra.
Kendati sistem penanggulanganh banjir Thailand yang canggih, Paribatra tidak dapat menjamin Bangkok tidak kebanjiran lagi. “Tapi setidaknya kami dapat memastikan banjir besar seperti 27 tahun lalu tidak akan terjadi lagi,” ujarnya.
Flood management in Chao Phraya River basin
Siripong Hungspreug, Wirat Khao-uppatum, Suwit Thanopanuwat1
Siripong Hungspreug is Director of Office of Budget Programming and Project Planning; Wirat Khao-uppathamis Director of office of Hydrology and Water Management; and Suwit Thanopanuwat is an expert on WaterResources Development Planning, all of Thailand’s Royal Irrigation Department.Sripong et al. Flood Management in Chao Phraya River BasinThe Chao Phraya Delta: Historical Development, Dynamics and Challenges of Thailand’ Rice Bowl 2
The Chao Phraya Rivers and her tributaries, have played a major role in thenation’s history from the periods of Sukhothai to Ayutthaya and Bangkok at present.Their existence was critical to the growth of the Kingdom of Thailand and fostered thedevelopment of major cities, including the capital city. In Ayutthaya Period, Thai peoplewisely used a long inundation during flood time in the Delta as the natural barriersagainst her country’s enemy. The floodplains of these rivers also provide some of themost productive farmland and continually contribute to the economic growth of thecountry. The high level of investment in the infrastructure for flood reduction wereconstructed to minimize the annual risk. But naturally, in the Chao Phraya Delta, floodhas continuously been experienced every year due to hydrometeorological andgeographical condition.
The flood of 1995 demonstrated that people and their properties in the floodplains of ChaoPhraya River basin were at risk. Excessive rainfall and related runoff inundated nearly15,000 sq.km. of floodplains and caused major damages to agricultural land andcommunities along the river. The inundation nearly exceeded 16 billion cu.m., dike breachingand over-topping occurred at almost every reach of the rivers. However, the extensiveinundation considerably relieved the urban areas located further downstream, like Bangkokand its satellites, from a serious disaster. Overall damages were extensive with about 72billion Baht and a large amount of unquantifiable impacts on the health and well-being of thepopulation. The Royal Irrigation Department thus initiated a formulation of an integratedstrategy plan of flood mitigation in the Chao Phraya River Basin in an inter-agencycooperation manner during December 1996 and August 1999. The plan was formulated withstructural and nonstructural measures covering the use of the floodplain by preservation ofpresent natural retarding effect ; assurance of safety level of major cities, enhancement ofsafety level in agricultural area, and an institutional arrangement for implementation ofmeasures.
1 Flood management in Chao Phraya river basin
1.1 Chao Phraya river basin
The Chao Phraya River Basin as shown in Figure 1 is Thailand’s largest and most importantgeographical unit in terms of land and water resources development. It is located in thenorth and central regions of the country and occupies about 35 percent of the country’s totalarea. About 20 million people (30 percent of the population) reside in the basin in which morethan 70 percent are farmers. Rice is the main crop in both irrigated and rainfed areas of thebasin.
Average annual rainfall in the basin ranges from 1,000 to 1,400 mm. The climate isdominated by the Southwest monsoon, which occurs between May and October. About 90percent of annual rainfall occurs during this period, causing heavy floods. The scarcity of rainbetween November and April makes agricultural conditions unfavourable. On average, thetotal volume of available water is estimated at 31,300 million cu.m. per year.
1.2 Characteristics of the basin’s upper and lower reaches
The river basin can be characterized geographically into upper and lower basins. The upperbasin is mountainous, with 40 percent forest cover and 41 percent cultivated land.Traditionally, agriculture has been practiced in the river valleys. Shifting cultivation hascaused soil degradation and erosion in some areas and has changed the hydrologicalregime. The lower basin (the river’s delta) is the floodplain and is well suited to ricecultivation. After irrigation water became available in the 1970s, farmers in the lower basinswitched from growing floating rice to cultivating higher-yielding varieties.
Among the basin’s major infrastructure, the Chao Phraya barrage irrigates an area of about1.2 million ha in the lower part of the river basin to increase wet season rice production. Themultipurpose Bhumibol and Sirikit dams are located upstream of the barrage. Theirconstruction enabled provision of water to 400,000 ha of dry-season cropping in the lowerpart of the river basin. Hydropower from these dams has become a major source of electricalenergy for Thailand.
Flood protection is important in the lower part of the river basin because of the risk of largescaledamage to public and private property. Dikes were constructed downstream of theChao Phraya barrage to prevent the inundation of cultivated land from small flood. Residential area were also protected by dikes and polder system at a higher safety level,together with a number of pumping stations, especially in the downstream-most of the river,Bangkok and vicinities.
The Chao Phraya River is the principal source of water for domestic and industrial uses inthe basin. The major user is the Bangkok Metropolitan Water Work Authority (MWWA), withan annual requirement of about 1,100 million m3. This amount has been supplemented with groundwater. The MWWA intends to terminate the use of groundwater and replace it with transferring water from the Mea Klong basin. Presently, less than 10 percent of water use in Bangkok comes from groundwater.
2 Floodplain management
From history of the country, the capital of Thailand in each era is always located in thefloodplain of Chao Phraya River Basin in the bank of the river and its tributary. Thai people inthe former time were accustomed with river flood and developed the way of living in this vastfloodplain and had wisely used a long inundation during flood time in the Delta as the naturalweapons against her country’s enemy. Until recently, from 1970, when a modern waterresources development scheme were constructed and significantly improve the livingcondition, enhance economic activities through better regulation of water and reduction offlood in the delta.
Though efforts have been made to mitigate flood damage in the Chao Phraya River Basinthrough the construction of dams, reservoirs, dikes and pump stations, flooding problem stillpersists due to the increase of flood discharge as a result of deforestation, expansion offarmlands and urban areas, etc., in line with the economic growth.
The flood damage potential is increasing due to rapid urbanization and land development indownstream areas, particularly, the Bangkok metropolitan area and other municipalitiesalong the Chao Phraya River. A disastrous flood occurred in October 1995, resulting in theextensive damage to properties and loss of human lives.
2.1 Causes of floods
The causes of floods, in general, may come from two main sources: nature and humanintervention, as follows:
2.1.1 Natural causes
The main natural causes are overbank flow of the rivers, heavy rainfalls and tides.
Overbank flow : Floods in Thailand are also generally caused by overflow from the rivers,which results in widespread flooding. During the peak flood in 1995, the flow in the ChaoPhraya River passing through Bangkok metropolis to the Gulf of Thailand was much higherthan the capacity of the Chao Phraya River and caused severe flooding in the Chao PhrayaDelta and Bangkok metropolis.
Heavy rainfall : Heavy local rainfall is usually the main cause of inland floods, as it oftenexceeds the drainage capacity of the local areas or streams. For example, several tropicalcyclones passed through Thailand and caused heavy rains in 1995, including the depressionstorm “Lois”.
Influence of tides : Tidal fluctuation at the river mouth has often affected the drainage ofriver floods into the Gulf of Thailand. This effect prolongs the period of flooding, especially inthe coastal provinces of the Chao Phraya River basin, Samut Prakan, Bangkok metropolisand Samut Sakhon.
2.1.2 Man-made causes
The most common man-made causes in Thailand are deforestation, uncoordinated urbandevelopment, over-abstraction of groundwater, and destruction of flood embankments.
Deforestation : This is the most significant man-made cause that increases flood peak fromrainfall and reduces the lag time between rainfall and run-off. In a deforested area, surfacerun-off and peak flood discharge tend to be higher, since there are no trees to obstruct theflow. Moreover, the rapid run-off will increase erosion of soil surface particles, resulting inhigher turbidity and more serious sedimentation. This results in reducing function of the riverand water sources.
Uncoordinated development : In urban development, most of the surface areas arecovered with houses, roads or paved surface having lower water absorption and rainfalltends to convert almost immediately into run-off flowing into the drainage system. Thisphenomenon is in contrast to that in rural areas, where rainfall can be retained by vegetationcover and absorbed by soil. Many kind of development in delta area have related to creatinghigher flood risk for example protection of urban and high-value farm will reduce space offlood inundation accordingly such as orchards, aquaculture, etc. Construction of roads andrailways will also obstruct flow especially for inland flow. Housing construction in public areasalong river or canal banks is another example of action that reduces the stream cross-sectionand thus its flow capacity. Uncontrolled dumping of sewage and garbage may obstruct theflow and cause siltation in the drainage streams. As a consequence, uncoordinateddevelopment in many parts of the country has resulted in decrease in drainage efficiencyboth inland and river courses.
Destruction of flood embankments : There have been cases in which inhabitants living inareas outside the protection of flood embankments destroyed those embankments in thehope of reducing the flood-water level in their areas. Protection of these embankments wasdifficult, although there are government agencies responsible for the maintenance andmonitoring of the embankments. These events resulted in abrupt flooding of the protectedresidential areas.Over-abstraction of groundwater : Pumping of groundwater is one of the main causes forland subsidence, which has resulted in deeper flooding and longer waterlogging. Thegovernment agencies concerned are trying to limit the pumping of groundwater and this efforthas been emphasized in the Bangkok metropolitan Area.
2.2 An overview of past floods and developments
2.2.1 Past flood damage
Floods continue to cause annual damage in the Chao Phraya River Basin, as summarized intable below. It may be noted that the flood damage was estimated based mainly on thevalue of property damage and did not include the cost of lost production and other forms ofeconomic loss. The trend towards higher flood damage reflects a number of factors,including the higher value of property and the ongoing development of property more vulnerable to floods.
2.2.2 Major change in the flooding regime
Changes in the flooding regime in the Chao Phraya River basin reflect not only changes ineach factor causing flood but also in the interaction among them. While riverine floodingcaused by the overbank flow of the main river discharge remains an important cause formajor flooding and flood damage, the coinciding of floodwaves from the tributaries, urbanfloods and high tides appear to have become more frequent and are thus an increasinglythreatening factor. In order to give an overall picture of the flooding regime in the lower ChaoPhraya River basin, the most important causes of flooding in the three most severe floodsduring the past 60 years are briefly summarized in following table.
As Chao Phraya delta is the highest economic growth area of the country, the high level ofinvestment in the infrastructure, with the extensive development of natural resources over theyears in the basin, have led to a complex change in the flooding regime. This change is alsoeffected by the complexity in water resources management. Apart from the construction ofvarious storage reservoirs in the upper part of the basin, the following measures have been implemented:
2.2.3 Summary of past development
Overbank flow protection scheme : The dykes were constructed along both sides of theChao Phraya River banks from Nakhon Sawan down in to Bangkok under the supervision ofthe Royal Irrigation Department. Nowadays, these dykes of 300 km length are used ashighways. The regulators were installed at the confluence of the tributaries to controlbackwater flow from the Chao Phraya River. However, the dykes are incomplete in somepart, such as on the western side of Bangkok for which the Bangsai-Bangkok Highway isbeing temporarily used as a part of the dykes.
Flood control schemes for major municipal areas : There are seven major municipalitiessituated along the Chao Phraya River: Nakhon Sawan, Chai Nat, Singha Buri, Ang Thong,Ayutthaya, Patum Thani and Nonthaburi. The Public Works Department (PWD) plans toprovide flood protection to these cities by polder systems, which consist of retaining walls,embankments, regulators and pumping stations.
Flood control schemes for Bangkok and vicinity : The master plan for flood protection inthis area was launched in 1984. The first scheme was finished in 1995. According to thatscheme, 1,500 km2 will be protected from floods. The scheme consists of several initiativesof His Majesty the King, such as a 74-km dyke, starting from the Rangsit Canal down towardthe sea at Samut Prakan, and 20 pumping stations along the Chao Phraya River with a totalof 30 million m3/day. The construction of regulators and drainage systems in Nonthaburi andSamut Prakan is part of the scheme. According to the work plan of the Bangkok MetropolitanAdministration (BMA), a permanent concrete floodwall with a total length of 80 km along the Chao Phraya River will be constructed within the next five years together with increasing thedrainage capacity up to 65 million m3/day.
Flood control schemes of agricultural area : The Royal Irrigation Department (RID) hasestablished a flood protection and drainage for the agricultural area in the lower ChaoPhraya basin. Dykes have been constructed along the Bang Pakong River in the east, ThaChin River in the west and also the Chao Phraya River, to provide flood protection to anagricultural area of 5,000 km2. More than 50 regulators and pumping station with a capacityof 50 million m3/day were constructed.
2.2.4 Evaluation of the current flood control situation
An evaluation of the current situation of flood control in the basin is summarized below:
The upstream reservoirs have markedly helped regulate the flow regime. For a flood of themagnitude of that of 1995, corresponding to a 25-year flood, the flood peak at NakhonSawan, will be reduced by 1,000 m3/s, or over 20 per cent of the natural flood. It may benoted that the capacity of these reservoirs in flow regulation is also important in reducing thevolume of the floodwaves travelling down to the Bangkok region during the critical period.
The development and protection of large areas in the lower Chao Phraya basin, especiallyfor agriculture and urban development, have greatly reduced the natural capacity of the basinin dispersing and reducing the floodwaves when passing through this area.
The confinement of the river to its main channel in Bangkok, although not complete, has ledto an increase in the flood-water level resulting from an increase in the outflow to the sea.This fact has consequently required an increase in the level of protection against the riverfloods.
3 The 1995 Flood
The depression storm “Lois” in 1995 caused heavy rainfall in the north. Spillage of the SirikitDam and high discharges of the Nan, Yom and Chao Phraya rivers inundated large areas inthe Phrae, Sukhothai, Phitsanulok, Phichit and Nakhon Sawan provinces as well as all otherprovinces along the Cho Phraya River downstream of Nakhon Sawan as shown in Figure 2. Bangkok and vicinity suffered from the flood for more than two months. However, the citycore of Bangkok was saved by the flood protection system that had been constructed in1984. The flood in 1995 was considered a severe flooding event affecting the entire country.
The main causes of flooding are low flow capacities river channels. The present river channelcapacities are between 3,000 and 4,000 m3/s in the stretch near Nakhon Sawan, about 1,300m3/s in the upstream near Ayutthaya, about 2,900 m3/s in the downstream near Ayutthaya,and about 3,600 m3/s at Bangkok as shown in Figure 3. The flow capacity decreases towardthe downstream, this implies that spillage from the river channel gradually occurs in theupstream when a large scale flood occurs; hence, spillage do not concentrate in thedownstream. This situation contributes to alleviation of flood damages to Bangkok, while the spilled water is widely retained in the agricultural area in a manner of inundation for 2-3months. Huge inundation took place over 15,000 sq.km. Most of the floodwater wasgenerated in the Nan and Yom river basins. Firstly, the floodwater originated in the upperbasin then flowed down along the Nan and Yom rivers, repeating collection of tributaries’runoff water and spillage by overtopping and dike breaching. The total water volume whichswelled to 31 billion m3 at Nakhon Sawan then entered the delta areas and spilled over theriver banks to the adjoining flood plains caused inundation to nearly 16 billion m3. Thecontribution of local rainfall to the inundation in the Lower Central Plain, namely the Higherand Lower deltas, was not significant. The estimated flow capacity near Bangkok was about3,600 m3/s, or at its maximum capacity.
Besides the natural causes, it is pointed out the several causes of human interventionactivities such as land use in flood risk areas, development of upstream, operation of flowcontrol facilities such as dams, and coordination among agencies concerned on floodmanagement are with the increase in flood damage.
3.1 Flood damage condition
When floods strike, people try to protect their assets or mitigate flood damage by takingcountermeasures. Since inundation comes up slowly, people can determine when the floodcomes and have enough time to take countermeasures. Inundation level comes up severalcentimeters per day, and it took 20 to 30 days from the beginning of the inundation to reachthe highest level in the case of Ayutthaya in 1995. The flood information is frequentlybroadcast on radio and TV. People make efforts to move their assets such as furniture andtelevision to the second floor or an upper place like a shelf or desk in most cases. Shopowners construct protection walls made of cement.
Large factories are located around municipalities or sanitary cities in general. Most of thesefactories have their own dikes for protection against floods. They usually have large amountsof assets such as facilities, machinery, relatively protected against floods. However, oncethese are submerged, the damage amount becomes very large.
People have developed the wisdom of providing flood countermeasures through theirexperiences. However, they cannot prevent or mitigate big floods and, actually, muchdamage has been inflicted.
It is difficult to estimate the overall flood damage. Theoretically, it is divided into twocategories, tangible damage and intangible damage. The latter, which includes negativepsychological impact such as fear, depression and health, etc., cannot quantify in monetaryterms. Only tangible damage is further considered into two categories: direct damage andindirect damage. Direct damage is measurable and often referred to as the damage. Indirectdamage is not physical but subsequent negative effect on economic activities. Sales loss, forinstance, is a typical indirect damage due to business suspension in a shop forced to closeby inundation. Direct damage also includes loss of tourism and expenses for diseases andso on. Under the foregoing circumstances, estimation of flood damage in the 1995 floodamounts to about 72 billion baht. It was also estimated the future condition (20 year) when land use will be changed toward more urbanization, the magnitude of 1995 flood will increasedamage to 164 billion baht, as demonstrated in Figure 3.
3.2 Royal flood management initiatives and ongoing flood mitigationproject by agencies concerned
His Majesty the King has shown great concern for flooding in regions outside Bangkok bysuggesting various methodologies to suit local conditions and to conform with the availabilityof government officials and budgetary constraints.
The low-lying flat terrain of Bangkok causes floodwaters to drain from the area slowly Manycanals have a small gradient while others are silted or filled up. Weeds and other items blockthe flow of water. There are some of the factors why Bangkok and the surrounding area havebeen subject to heavy flooding for many years. His Majesty has devised a flood managementsystem for Bangkok which he calls Kaem Ling (Monkey’s Cheeks). The concept is totemporary storing water in some places at high tide and drain out at low tide.
Together with the Royal-initiated Projects, the agencies responsible for flood mitigation anddrainage works have made serious efforts under the following projects:
- Heightening of flood barrier at Bangkok Metropolitan Area by BMA
- Provision of polder system together with the improvement of drainage system by PWD
- River improvement and drainage system improvement by RID
- Loop-cut at Bangkok Port and construction of multipurpose dams by RID
- Monkey’s cheeks projects on the coastal area both east and west of Chao Phrayaestuary by BMA and RID
Through these projects, the flood protection level in major urban areas is, in general,expected to increase. However, protection works in the upstream sometimes bring aboutadverse influences to the downstream: i.e., the protection level in Bangkok is expected todecrease due to the construction of polder in Pathum Thani and Nonthaburi. For theagricultural areas it is expected that the present low protection level against floods ismaintained in the future.
4 Formulation of Master Plan
4.1 Basic concept for the formulation of master plan
- According to the past flood occurrence, flood conditions in the Chao Phraya River Basinis featured with the existence of extensive inundation areas, which play an important roleto retain flood discharge flowing into the Chao Phraya River, resulting in the mitigation offlood damage in the downstream. In this connection, the flood mitigation plan is formulated putting emphasis on preservation of the natural retarding effect. The conceptis a global one for flood mitigation through the provision of nonstructural measures andalso corresponds to the monkey cheek concept.
- On the other hand, the Chao Phraya River basin, especially the Chao Phraya Delta,tends to be developed continuously in the future, even in such natural retarding area,which results in the decrease of retarding effect causing the increase of flood dischargeto the downstream. To minimize the influence due to decrease of retarding effect,suitable measures for comprehensive flood mitigation including structural andnonstructural measures are introduced.
- Flood mitigation measures are also classified according to the flood, i.e., basin-wide floodor local inland water. The Master Plan is formulated by putting emphasis on floodmitigation measures for basin-wide flood. As for local inland water, the conceivablemeasures for drainage system improvement is examined for agricultural areas as well asthe prioritization for implementation of improvement works.
- The flood prone areas in the basin are mainly composed of urban and agricultural areas.Among them, the urban areas will take priority for flood protection because their socialand economic impacts are considered much higher than the agricultural areas. Urbanareas like Bangkok, Ayutthaya, Nakhon Sawan and others are to be protected byeffective measures against bigger scale floods.
- The agricultural areas play an important role as retarding area during big scale floods,and this role should be preserved. On the other hand, for small-scale floods, the presentflood damage condition should be improved, providing suitable measures within theallowable extent that will not cause adverse influence to the other areas.
- Flood damage conditions are influenced by nonstructural such as control of land andgroundwater extraction, and such influence would finally affect the effectiveness ofstructural measures. In this connection, the selection of an optimum measure is madethrough a comparative study on alternatives, considering the most effective combinationof structural and nonstructural measures.
- Although the purpose of the Master Plan is flood mitigation, it is also important toconsider the shortage of municipal water supply in the dry season. The multipurpose useof the proposed flood mitigation measures is thus examined, especially for irrigation andmunicipal water supply.
- Alternative 1, Partial Protection of Pathum Thani and Nonthaburi
- Alternative 2-1, Heightening of Flood Barrier
- Alternative 2-2, Diversion Channel
Integrated Flood Mitigation Management in the Lower Chao Phraya River Basin
- Topography of the basin. The Chao Phraya river has relatively steep slope basin in the upper part and mild slope in lower part. Such topography makes the flood flows rapidly in upstream and slow down in lower areas. Moreover, the influence of tide makes the flood situations become worse as it overflows to the both river banks where economic area is located.
- High discharge from the upstream e.g. flooded in the years 1983, 1995, 2002 and 2006.
- ocal heavy rainfall e.g. flooded in the years 1983, 1996 and 2002.
- Reduction of retention area along both bank of the river and Change of flow pattern. The cause is mainly due to:
- Reduction of the agriculture area due to rapid encroachment of the urbanization and industrialization which have their own protection system
- Flood protection schemes for agricultural area are implemented to reduce the damage to the agricultural product
- Land subsidence due to soft clay at delta area and over groundwater pumping. This lower down the flood embankment level and cause the difficulty for the local drainage thus increase flooding risk.
- The global warming. This create tendency of higher fluctuating of rainfall. In addition, sea level trends to be higher which effect to community and economics area in low land of Chao Phraya river. In general, the risk of flooding will increase in the future.
- Water level in the lowland shall keep minimum during the rainy season to have more storage for flood peak water. Water in the lowland shall drain out to the river through the gates in general, pump shall be used only when the incoming flood peak threat to damage the protected communities.
- In general, lowland can be used to store flood volume only once in a year, therefore diversion of excess flood peak to designated lowland shall commence when the river water level almost reaches its highest peak. Accurate forecast of peak flood is crucial for the flood operation management.
- Diversion of river flood peak to the lowlands shall start from the one located at the most upstream downward to downstream lowland.
- Land use in the Lowland shall be reserved and controlled as cultivation land, urbanization should not allow to minimize damages in the Lowland.
- Flood management criteria for the use of Lowland shall be set up along with decision support system. These include flood forecasting and warning system for the whole basin and Lowland area.
- Fair and fast damage compensation method and process due to the diversion of water into the lowland shall be agreed by the stakeholders.
- 5 Lowland Areas in the Upper Chao Phraya River Basin. The 5 Lowland areas with 835 sq.km. can accommodate flood volume of 1,161 mcm. Benefit can be claimed from the communities in Phitsanulok and Pichit provinces which located along the Yom and Nan Rivers. The said flood volume amount could effectively lower down flood level from 0.2 to 1.2 meters and help alleviate flood with return period less than 5 year.
- 8 Lowland Areas in the Lower Chao Phraya River Basin. The 8 Lowland areas with 925 sq.km. can accommodate flood volume of 1,738 mcm. Benefit can be claimed from the communities in provinces located along the lower Chao Phraya river bank which include Signburi, Angthong, Ayuthaya, Phratum Thani, Nonthaburi and Bangkok metropolitan. These group of Lowlands could help alleviate flood for a specific range of discharges, released from the Chao Phraya Dam, amounted from 3,000 to 4,200 cms. which corresponding to the flood of 5.5 to 20 year return period. The effectively lower down of flood level is from 0.2 to 1.0 meters.
- Compensation of damage in Lowland due to divert in flood water will be paid reasonably to the market price and quickly.
- People living in the Lowland gain the benefit from the flood protection and drainage system infrastructures development.
- People have the opportunity to participate in the project management.
- Retention level in the area will be higher than the specified.
- Retention period will be last too long.
- Compensation will not be paid.
- Royal Irrigation Department and concerned agencies should built up the confidence to people by disseminate the information, news and facts periodically and continuously.
- Stake holder should participate in the project implementation every step from the project preparation, survey, detailed design, construction and project management.
- The uncontrolled land use development in lowland as well as the effect of climate change on the hydrological and meteorological design conditions.
- Government policies and sanction facilitating to Lowland area development, such as the issue of regulations/laws/Acts and enforcement for damage compensation fund and land use plan of the Lowland.
- The concreteness and stability of management organizations
- Decision support systems and database used for management
- Procedure of public participation in every stage of development to draw out the recommendation from the people in the areas to adjust the development in compliance with their requirement until their acceptance is achieved.
- On the North (the Pasak River), there is the Pasak Jolasid Dam located upstream. The dam can regulate to control maximum discharge of 800 cms. A 36 km-long dike is also equipped along the Pasak river. There is also the Raphiphat canal receiving water from the Pasak river of 120 cms at maximum before distributing it to 17 irrigation canals through the East of Lower Chao Phraya irrigation subprojects lining from the north to the south.
- On the West (Chao Phraya River and King dike), a 120 km-long dike is constructed to protect spillage of flood water into the irrigation area and to protect the inflow of water from the irrigation area to the city. Along the dike, regulators are constructed at the canal crossing. Pumps are equipped at some specific gates which can drain water to the Chao Phraya River with the maximum discharge capacity of 203 cms or 14.9 MCM per day.
- In the East (Nakhon Nayok and Bang Pakong rivers), there is a 145 km-long dike equipped with regulators and pumped which can drain water with the maximum discharge of 169 cms or 10.6 MCM per day.
- In the Lower part (Gulf of Thailand), there is a 39 km-long dike protecting sea water intrusion and high flood levels in the canals. There are also regulators equipped with pumps with the maximum discharge of 345 cms or 23.9 MCM per day. Moreover, there is the Suvarnabhumi drainage canal which can drain water out of the area of Suvarnabhumi Airport with the maximum discharge of 100 cms through the pump.
- For drainage within the east of the Lower Chao Phraya irrigation area, there are many canals lining along the north to the south and the east to the west with total length of 300 km. There are also regulators and pumps which pump water out along the east to the west with the maximum discharge of 156 cms.
- Water stored in the irrigation area shall divert to the Nakhon Nayok and Bang Pakong rivers as much as possible using the existing east-west canals. At the same time water levels in the both rivers shall be manipulated correspondingly by regulating discharge released of the Khun Dan Prakanchon Dam. Internal flow direction can be forced using existing regulators and pumping stations installed at the internal drainage canals.
- Gates shall be operated to drain water out with optimum use of tide fluctuation while internal drainage shall be regulated correspondingly.
- Monitoring stations shall be defined for flood warning and decision on management operation.
- Water level in the internal canals and ponds shall lower down to free the storage for the incoming storm of 200 mm of rainfall. These could be done by empty 50% of storage in the existing 112 MCM pond and lower down water levels in the canals and low lying area by 0.2 meter.
- Water levels in various canals and flood volume shall be forecasted using the existing 48 rain gauge stations and tide prediction. Results shall be used to managing water in the irrigation area.
- Since the project area covers several sub irrigation projects which are under the responsibility of various agencies, it is recommended to the set up joint working group consist of member of each agency. The working group shall work together to share and synchronize the operations.