FLOOD CONTROL United Nations JOURNAL st/ecafe/ser.c/26 March 1956 Economic Commission for Asia and the Far East CONTENTS Page INTRODUCTION .................................................................................. 1 TRACKS OF TYPHOONS DURING 1955 4 DAMAGE DONE BY TYPHOONS, FLOODS AND DROUGHTS IN VARIOUS COUNTRIES OF THE REGION DURING1955 .... 8 Burma ......................................................................................... 8 Ceylon ....................................................................................... 11 China ........................................ 12 Taiwan .................................................................... 12 Mainland .................................... 13 India ......................................................................................... 14 Andhra .................................................................... 18 Assam ...................................................................... 18 Bihar ...................................................................... 20 Madhya Pradesh ................................................. 27 Madras .................................................................... 28 Orissa .................................................................... 29 Punjab, Delhi and Pcpsu ........................... 32 Rajasthan ............................................................. 38 Travancore-Cochin ......................................... 38 Uttar Pradesh ................................. 39 West Bengal ................................. 45 Indonesia ............................................................ 46 Japan .............. 48 Malaya ....................................................................................... 58 Pakistan ............................................. 60 Philippines ........................................................................... 65 Thailand .................................................................................. 72 - 1 - INTRODUCTION An account of the typhoons and floods which caused havoc in the various countries in Asia and the Far East, during 1952, was given in the June 1953 issue (ST/ECAFE/SER.C/15), of the Flood Control Journal. Information for 1953 was included in the March 1954 issue (ST/ECAFE/SER.C/18) and that for 1954 was published in the March 1955 issue (ST/ECAFE/SER.C/22). Similar information for the year 1955 is given in the following pages. The atmospheric disturbances which play an important role in river flood and drought during south-west monsoon season are the inter-tropical convergence zones and the revolving storms. The inter-tropical convergence zone is seasonal in its character. Usually heavy rains occur within this zone, because two streams of air, one from the cold north and drier (continental in origin) and the other from the warm humid south (maritime air), come into conflict. The revolving storm or cyclonic storm is classified according to its force as follows: 1. Depression having cyclonic circulation with winds up to 33 knots 2. Tropical storm having cyclonic circulation with winds up to 34-36 knots 3. Typhoons having cyclonic circulation with winds 64 knots and upward. Both the depressions as well as the tropical storms not only bring torrential rainfall, but also serve as inductors to bring back the activity of the south-west monsoon. The major area where the storms originate is in the west Pacific while the minor area is in the China Sea as shown in figure 1, Usually they are born in the form of typhoons, tropical storms, or depressions and increase in their severity when moving over the water surface of high moisture, and then become weakened as they enter the land surface due to high barriers and less moisture. In general, the storms have three routes; one to Japan, other along the China coast, and the third one right into the former Indochina. These storms almost die out when they arc forced to rise along the coast. These storms have no chance to reach as far as Thailand, but the /cyclonic - 2 - cyclonic influence itself and the activity of the south-west monsoon revived by the cyclonic action result in an additional large amount of rainfall over the country besides that from the normal south-west monsoon. As the average frequency for monthly occurrence of this Indochina storm during the south-west monsoon season indicates the highest in September, September is the month in which fairly frequent and large amount of rainfall occurs in Thailand. Besides the storms sometimes move further inland, after reaching the former Indochina coast, to enter Thailand from the east in the form of depressions or tropical storms, and they cause various rivers to be flooded. The average frequency for annual total occurrence of the storms in south-east Asia is as much as 22 and only 2 or 3 of these strike Thailand. The seasonal distribution of tropical storms which struck Thailand as observed during the period 1938 to 1951 by the Meteorological Department of the Royal Thai Navy is as follows: Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec Total 0 0 0 0 0 0 0 2 0 4 1 0 7 and the distribution of depressions which occurred or passed through the country during the period is: Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec Total 0 0 0 0 1 0 1 0 4 7 7 3 23 The percentage of frequency of their visit to various parts of Thailand is as follows: 63 per cent passed the Gulf of Thailand and south of Thailand, and 19 per cent passed over the central plain of Thailand. It may be seen clearly that tropical storms and depressions directly strike Thailand towards the end of south-west monsoon. In a period of 15 years, i.e. from 1938-1953 the severest single tropical storm which struck Thailand was the violent tropical storm of 22 October 1952 which swept over the east coast of the Gulf of Thailand and over the southern portion of the Central Plain between 22 and 23 October 1952. The resulting rainfall on 22 October (24-hour rainfall) appeared to be very torrential: /Stations MONTHLY FREQUENCY OF THE OCCURRENCE OF CYCLONIC STORM. average frequency for annual occurrence 22/yr. FIGURE I MAP SHOWING the cyclonic STORM TRACKS IN SOUTHEAST ASIA v a n A p r July May Jun No Oct Dec Sept Aug Feb M ar J - 3 - Stations 24-hr rainfall in mm Normal monthly rainfall for October in mm Chantaburi 336.8 183.6 Sattahib 302.7 185.5 Bangkok 111.0' 229.5 It was fortunate that this storm swept only over the coast and not over the watershed of the main rivers, thus playing no important part in the river floods. The other important characteristic of the cyclonic storms which cause continuous heavy rainfall and culminate in a flood problem is that once a tropical storm or depression strikes in a wide front over the main watershed of the major river, another severe storm follows within a week's time. In consequence of the superimposed actions of the storms there is a continuous torrential rainfall. This results in rising base flow in the rivers and the storm run off superimposed gives an extensively high flood, both in peak and in volume. During the past fifty years such a condition has occurred in Thailand only once in September 1942, which caused the great flood in the Chao Phya river and resulted in damage to 34 per cent of the rice crop, railroad, highway and towns and liverstock. The total damage was estimated at 72 million baht. The south-west monsoon alone, however, is not sufficient to replenish the supply of water for Thailand. Should there be no additional cyclonic storm rainfall, the result is always likely to be a bad drought towards the end of the season by which up to 40 per cent of rice crop is damaged, such as in the year of extreme drought in 1919 as shown is figure 2. Typhoons and floods which caused havoc in this region during 1955 are described in a separate section and an attempt has been made to correlate them as far as possible. It has been noticed that while certain parts of a country are afflicted with floods other parts of the same country are suffering from drought. In this issue, therefore, information on droughts also has been supplied: /The description - 4 - The description of floods and typhoons given in the following paged is generally based on the information very kindly supplied by the irrigation and meteorological departments or weather bureaux of China: Taiwan, India, Japan, Pakistan, the Philippines and Thailand. Were the data was not received from the governments concerned information was oftained from news items appearing from time to time in the various dailies of the different countries of the region. For this reason the information may not be quite comprehensive. Every attempt has been made, however, to form as exact a picture as possible. TRICKS OF TYPHOON DURING 1955 Typhoons which originated in the Pacific Ocean, the China Sea and the Indian Ocean during the different months of the year 1955 are listed in table 1. Figure 3 shows the tracks of typhoons which originated during the period from January to September and figure 4 those from September to December 1954. /Table 1. c.m .s. — FIGURE 2 MEAN DAILY DISCHARGE HYDROGRAPHS OF SEVERE FLOOD, NORMAL & SEVERE DROUGHT YEAR CHAOPHYA RIVER AT WAD-THA- HARD, CHAINART discharge (THAILAND) drought period towords the end of the season April May June July August September October November December January February March Irkutsk Chita SAKHALIN USSR Ulan Bator Khobarovsk MONGOLIAN PEOPLE'S REPUBLIC Harbin Changchun Tihwo Vladivostok CASPIAN Alma Ata (Urumchi) Fushun Tashkent Peking