Flood Risk Management in Hat Yai, Thailand By: Royal Irrigation Department

The most rapid economic growth city, and the most populated urban area in Southern Thailand

One of Largest commercial and tourist city in the Southeast Asia region

The center of trades of the Southeast Asia

Hat Yai, the largest commercial and tourist city in southern Thailand Hat Yai, the largest commercial and tourist city in southern Thailand. It is located in low-lying areas at the base of a roughly circular valley. It is also prone to inundation from the Utaphao River, which flows through its heart often in concrete channels that provide limited drainage. The Utaphao river basin is located in southern Thailand. The river rises at Sadao, on the border with Malaysia, and flows generally northwards to meet Songhkla lake. The catchment area is approximately 2,500 km2 . Location of Utaphao river basin and characteristic of the river basin.

High Frequency of Flood Risk Hat Yai had been under a series threats of floods for many years: 1833 1916 1942 1959 1961 1962 1966 1967 1969 1972 1973 1974 1976 1981 1983 1984 1988 2000 2003 2008 2009 Floods occur almost every year !!! Big floods 1973 1983 1,000 Million THB 2000 massive losses

Serious flooding occurred in 1988 and again in 2000 Serious flooding occurred in 1988 and again in 2000. Flooding in this city is recognized as a serious disaster in terms of the frequency, level of risk, and affected areas.

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Flood Mitigation of Utaphao river basin and Hat Yai city 1. Structural measures Improvement of natural water drainage system, natural canal extension to improve drainage efficiency of canal for a distance of 46.90 km. Flash flood drainage management, main drainage system work including a water gate to transfer water from Utaphao canal to Songkhla lake (length 21.343 km). A water diversion canal (length 26 km) and water gate will drain water from Utapho canal outside Hat Yai town and relief flood in lower Utaphao canal.

Flood Mitigation of Utaphao river basin and Hat Yai city A diversion canal was built to discharge excess flow directly to the sea. Construction of embankments, improvement of drainage canals Reservoir area improvement Reservoir area water way construction Provision of drainage pumps.

Songkla lake Rama 1 Flood canal Rama 4 Flood canal Rama 3 Flood canal Rama 5 Flood canal Rama 6 Flood canal Hat Yai city Utapao flood gate Khlong Utaphao Natural canal Flood diversion canal Blue line is natural water drainage system in Utaphao river basin, natural canal extension to improve drainage efficiency of canal for a distance of 46.90 km. red line is flood diversion canal (length 26 km) and water gate will drain water from Utapho canal outside Hat Yai town and relief flood in lower Utaphao canal. flood gate

Flood gate in main canal Flood gate in sub-canal Diversion canal Flood gate in main canal Flood gate in sub-canal Diversion sub-canal

2. Nonstructural measures Monitoring the climatic and hydrologic situation of the Utaphao River using information from Thai as well as foreign meteorology websites. Water situation prediction and mitigation consist of climate, rainfall, discharge, water level monitoring in reservoirs, rivers and typhoon. Water management in the watershed to indicate mitigation and flood warning level. Public warning for advance flood preparation to relief damage of prosperities and lives. Water analysis center at Songkhla Irrigation project.

High Potential of Observations and monitoring Meteorology: TMD Doppler Radar Regional Met. Center to be a major department to closely monitor &/ give essential advices/ warnings Dense observation networks, accessible satellite data, and 4. Numerical Precipitation prediction Model (NWP/ WRF)

Telemetering network & Radar coverage

Utaphao river basin Telemetry System Real-time telemetry in Utaphao river basin consists of one main station and 13 field stations. It measures rainfall and discharge every 15 minutes. Data are sent via a VHF radio network to the main station for data analysis and flood prediction. Flood warning is provided 9 to 16 hours in advance. The efficiency of the telemetry system will be increased when we add a GPRS system and 5 more field stations.

Telemetry System in Utaphao river basin Malaysia Remote station Master station river Hat Yai city Telemetry System in Utaphao river basin

Flood forecasting and warning system FloodWork Server was located at the Royal Irrigation Department Southern Regional HQ in Hat Yai. This server was linked to a telemetry computer which receives all of the latest observed hydrological and hydraulic data from the Utaphao basin. Automated forecast simulations were set up, so that forecast simulations are carried out at regular intervals, ideally just after the telemetry system has been set up. Series of client computers, connected via leased line network connections to the main flood forecesting server, were set up to display the results of the flood forecast simulations

Flood forecasting system for the Utaphao River Basin using the Floodworks software (MWH Soft) FloodWork result for Utaphao river basin.

Flood forecasting by water level (state correlation) Flood forecast and warning in Hat Yai town using discharge data collected at different points along the Utaphao Canal can provide flood warning in advance of 20 to 21 hours. The flood routing period is variable, according to discharge in Utaphao canal. We developed statistical relationships between the flood peaks of two hydrological stations upstream of Hat Yai city and used the relationship to predict floods in the city. The two stations include X.173A (37 km above Hat Yai town) and X.90 (14 km. above Hat Yai town).

Flood forecasting by water level (state correlation) Khlong Utaphao Utaphao flood gate Ban Bangsala Ban Muangkog 23 km. 12 km. 17.85 m. 16.90 m. 15.60 m. 7 hr. 12 hr. 18-19 hr. 9.51 m. 8.87 m. 8.00 m. Flood forecast and warning in Hat Yai town using discharge data collected at different points along the Utaphao Canal can provide flood warning in advance of 20 to 21 hours. The flood routing period is variable, according to discharge in Utaphao canal. We developed statistical relationships between the flood peaks of two hydrological stations upstream of Hat Yai city and used the relationship to predict floods in the city. The two stations include X.173A (37 km above Hat Yai town) and X.90 (14 km. above Hat Yai town).

State relationship between X. 173A station, X State relationship between X.173A station, X.90 station and Khlong Utaphao gate X.173A station X.90 station Utaphao flood gate 23 km. 12 km. 12 hr. 3 hr. +16.90 m. 213.00 m3/s +8.87 m. 441.00 m3/s Q Rama1 = 220 m3/s Q = 400 m3/s Q = 620 m3/s Closely monitor If water level at X.173A rises to 16.90 m, water will arrive X.90 within 12 hours and rise to 8.87 m. Water will move from X.90 to Utaphao water gate within 3 hours. The total time period for this to happen is 15 hours with a total discharge value of 620 m3/s. Water management by 400 m3/s drainage along Utaphao Canal (water level in Hat Yai is 0.76 m. lower than the river bank) and 220 m3/s drainage along King Rama1 water way caused flood in some upper area of Utaphao water gate. The solution is water pump setting. This case didn’t affect flood in Hat Yai town.

State relationship between X. 173A station, X State relationship between X.173A station, X.90 station and Khlong Utaphao gate X.173A station X.90 station Utaphao flood gate 23 km. 12 km. 7 hr. 2 hr. +17.85 m. 346.00 m3/s +9.51 m. 774.00 m3/s Q Rama1 = 465 m3/s Q = 465 m3/s Q = 930 m3/s Flood warning If water level at X.173A rises to 17.85 m. (346 m3/s discharge), water will arrive X.90 within 7 hrs and water levels in the river will be 9.51 m high (774 m3/s discharge). Water will then travel from X.90 to Utaphao water gate within 2 hrs. The total travel period for the runoff will be 9 hours giving an advance warning period of 9 hours. The total runoff discharge for this situation is 930 m3/s. Floodwater management using the Utaphao Canal to drain away 465 m3/s (at its maximum capacity) and another 465 m3/s by the King Rama 1 waterway still resulted in floods in some areas around Hat Yai city since Hat Yai city is 0.29 metres lower than the river bank. A further solution to reduce the flooding problem in Hat Yai is to pump some of the floodwaters into Songkhla Lake. Although this measure prevented flooding at Hat Yai, flood warning and disaster preparation for the city is still needed in case flooding occurs in worse case scenarios.

Water management by pump setting 17 Pumping station in upper Utaphao river basin Water pumping preparation is necessary during floods. The types of water pumps used at Hat Yai include permanent pumps as well as temporary pumps set up when their need arises, depending on the rainfall and flood situation Water management by pump setting

Assistance/ support needed in UFRM Guidances & technical supports: 1. Expertise in QPE/ QPF development and improvement 2. Technology/ expertise in Flood Modeling improvement and inundation flood map

Conclusion: ## To reduce losses of lives and economy due to floods in city,…… urban flooding management strategy from meteorological aspect needed to be formulated and implemented properly. ## The disastrous impacts can be managed ………….by suitably implementing flood management measures, with collaborative efforts of all sectors of the whole community. ## Hat Yai is ready to participate in the Pilot City in the UFRM program of Typhoon Committee

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