Hydrological Condition Report including the issues of High Flow Fluctuation in Chiang Saen Technical Symposium for ESCIR and MRC on Social Impact Assessment in River Basin Management Sothea KHEM, HENG Suthy IKMP/TSD/MRCS 1-2 July, 2015 Ho Chi Minh City, Viet Nam
1. Overview of Seasonal Hydrological Trend in the LMB
Trend Analysis on Seasonal Change of Flows at the Upper Station of the Mekong Mainstream (1960-2014) Annual Flow,[cms] Annual Flow,[cms] 7500 6500 5500 4500 3500 2500 2500 2300 2100 1900 1700 1500 1300 1100 900 700 500 Pre-Dam 1995 Post-Dam Pre-Dam 1995 Post-D Trend of Annual Wet Season Flow at Chiang Sean (1960-2014) Annual Flow196019-94 R² = 0.1664 Trend of Annual Dry Season Flow at Chiang Sean (1960-2014) Annual Flow 1960-1994 R² = 0.0022 R² = 0.4897 1500 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Year R² = 0.0963 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Year Annual Flow,[cms] Annual Flow,[cms] The Trend of Annual Wet Season Average Flow at VTE 10000 (1960-2014) R² = 0.1247 9000 R² = 0.1172 8000 7000 6000 5000 4000 Dry Season Annual Flow 1960-1994 P>0.05 P<0.05 Wet Season P<0.05 P>0.05 P<0.05 P>0.05 3000 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2 Year The Trend of Annual Dry Season Average Flow at VT (1960-2014) 3000 2800 2600 R² = 0.0103 R² = 0.1702 2400 2200 2000 1800 1600 Annual Flow 1400 1960-1994 1200 Dry Season 1000 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2 Year
Annual Flow,[cms] 27000 22000 17000 12000 7000 Pre-Dam 1995 Post-Dam The Trend of Annual Wet Season Flow at Pakse (1960-2013) R² = 0.0996 Annual Flow 1960-1994 P>0.05 R² = 0.035 2000 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Year Annual Flow,[cms] 32500 27500 22500 17500 12500 Wet Season R² = 0.1137 Pre-Dam 1995 Post-D The Trend of Annual Wet Season Flow at Kratie (1960-2013) Annual Flow 1960-1994 P>0.05 R² = 0.0054 7500 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 201 Year Annual Flow,[cms] 5000 4500 4000 3500 3000 2500 The Trend of Annual Dry Season Flow at Pakse (1960-2013) R² = 0.0443 Annual Flow 1960-1960 R² = 0.0264 P>0.05 2000 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Year Dry Season Annual Flow,[cms] 7000 6000 5000 4000 3000 2000 1000 The Trend of Annual Dry Season Average Flow at Kratie (1960-2013) R² = 0.1504 R² = 0.0087 Annual Flow 1960-1994 P>0.05 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 201 Year
Annual Percentage Deviation of Rainfall at some selected Stations of the Mekong Mainstream (1966-2014) Threshold: +12 Threshold: -12
Threshold: +12 Threshold: -12
Summary Since 1995, the flows in Wet season at Chiang Saen to Vientiane showed significantly declined comparing to the pre-dam period. While, the Dry Season flow at Chiang Saen to Vientiane showed significantly increasing. However, it is found that there is no significant change/affect to the flow regime from Pakse to Kratie during the wet and dry seasons. The rainfall found essentially varied from place to place, referred to the topographical features of the watershed catchments in the LMB The potential changes of hydrological regime at Chiang Saen to Vientiane might be influencing by the reservoir operation on Mekong-Lancang in China. However, there was no significant influent to the further downstream of Pakse and Kratie.
2. Water level fluctuation at Chiang Saen
Fluctuated Water Level at Chiang Saen Station Water level (m) 8 7 6 5 4 3 2 1 Low Water Level in Dry Season at Chiang Sean, Compared with its Long Term Average 1961-2013 (Nov-Dec 2009 and Jan-May 2010) 0 20 40 60 80 0 100 1-Nov 16-Nov 1-Dec 16-Dec 31-Dec 15-Jan 30-Jan 14-Feb 1-Mar 16-Mar 31-Mar 15-Apr 30-Apr 15-May 30-May Fluctuation of WL Rainfall (mm) Average 2009-10 Date: 2010 River: Mekong Country: Thailand Flood Stage: 11.80m Alarm Stage: 11.50 m Rainfall (24h): 0.0 mm Date: 2013-05-20 River: Mekong Country: Thailand Flood Stage: 11.80m Alarm Stage: 11.50 m Water level: 3.72 m Rainfall (24h): 36.4 mm 9
Water Level Fluctuation at Chiang Saen in 2014 Fluctuation Precipitation (mm)
Hydrograph of Wet Season 2014 at Other Stations Flood Level:23 m Fluctuation: 14 m
Wet Season in 2014 Chaing Saen Luang Prabang Vientiane Pakse Kratie
Monthly distributed Rainfall in 2014 over LMB Heavy Rainfall Rain gauge Mean annual rainfall 2007-2013 (mm) Rainfall 2014 (mm) Percentage (%) Chiang Saen 1671.75 1721.00 +3 Luang Prabang 1359.00 1267.00-7 Vientiane 1663.88 1962.00 +18 Mukdahan 1419.50 1281.00-10 NakhonPhanom 2114.13 2242.00 +6 Pakse 1681.00 1527.00-9 Phnom Penh 1493.38 1156.00-23 TanChau 1161.25 1027.00-12 13
Annual Accumulated Rainfall Distribution over LMB 2013 (Source: 203.159.29.12/MRC_Data/Data/ /) 2014
Calendar day 350 300 250 200 150 The Onset and Offset Monsoon 2014 The start and end dates of the annual flood season at Vientiane between 1960 and 2014. 100 Start day End day Apr Year 50 1957 1964 1971 1978 1985 1992 1999 2006 2013 2020 Dec Nov Oct Sep Aug Jul Jun May Station Average Date Monsoon Onset 2014 Onset Date Average Date Monsoon Ofset 2014 Ofset Date Chiang Saen 9 th May 02 th May 8 th November 05 th November Luang Prabang 23 th May 28 th April 28 th October 04 th November Vientiane 5 th May 28 th April 14 th October 06 th November Mukdahan 9 th May 14 th May 8 th October 24 th September NakhonPhanom 6 th May 13 th May 9 th October 23 th September Pakse 9 th May 09 th June 11 th October 01 st October Phnom Penh 1 st June 09 th June 15 th November 11 th November TanChau 21 th May 15 th June 21 th November 05 th December
12 Hydrograph of Wet Season 2014 at Prek Kdam, Compared with its Exceedance Probability (P%): 1960-2013 (Jun-Dec, 2014) 0 Water level (m) 10 8 6 4 2 50 100 150 200 250 Precipitation (mm) 0 1-Jun 16-Jun 1-Jul 16-Jul 31-Jul 15-Aug 30-Aug 14-Sep 29-Sep 14-Oct 29-Oct 13-Nov 28-Nov 13-Dec 28-Dec Fluctuation Preci-2014 Average P10 P20 2014 300 Water level (m) 6 5 4 3 2 1 0 Hydrograph of Wet Season 2014 at Chau Doc, Compared with its Exceedance Probability (P%): 1980-2013 (Jun-Dec, 2014) 0 50 100 150 200 250 Precipitation (mm) Water level (m) 6 5 4 3 2 1 Hydrograph of Wet Season 2014 at Tan Chau, Compared with its Exceedance Probability (P%): 1980-2013 (Jun-Dec, 0 2014) 50 100 150 200 250-1 300 0 300 1-Jun 15-Jun 29-Jun 13-Jul 27-Jul 10-Aug 24-Aug 7-Sep 21-Sep 5-Oct 19-Oct 2-Nov 16-Nov 30-Nov Fluctuation Preci-2014 Average P10 P20 2014 14-Dec 28-Dec 1-Jun 15-Jun 29-Jun 13-Jul 27-Jul 10-Aug 24-Aug 7-Sep 21-Sep 5-Oct 19-Oct 2-Nov 16-Nov 30-Nov Fluctuation Preci-2014 Average P10 P20 2014 14-Dec 28-Dec
The Flood Peak Index of Annual Flow and Food Volume at Kratie The 3 boxes explain the annua flood variables (peak and volume) above and below of mean values; 1. The dots within the inner box are considered as variation between years normally expected (average conditions) 2.The dots in the 2 nd box are considered as the years with significant flood & low-flow Mean Volume 271Km 3 3. The dots outside of the 2 nd box are considered as historically extreme flood & low-flow years 17
Conclusion in Wet Season 2014 1. From Chiang Saen to Vientiane during the 2014 wet season was characterized as significantly below the normal year (Low Flow), which could be partly attributed inflow at upstream (Hydro-power Operation.) 2. The flows at Pakse to Kratie were reached to the maximum levels during the early wet season (Jun-July) which influencing by the heavy rainfall and inflow from theirs tributaries. However, the flow was gradually decreased even below long term average from Aug till end of the wet season. 3. The inflow into the Tonle Sap Lake was high in early July, but drastically decreased from Aug onward. The volume of tonle sap lake in this wet season found lower then long term average condition. It leads to the significant low outflow. Chaing Saen Nong Khai Pakse Kratie 18
Dry Season in 2015 Chaing Saen Luang Prabang Vientiane Pakse Kratie
The Dry Season Flow Monitoring from Chiang Saen to Kratie (Nov., 2014 to May 2015) Chiang Saen Vientiane Fluctuated WL Fluctuated WL Pakse High WL cond. Kratie High WL cond.
Provided Information by China on the Dry Season Flow 2015 Based on a request from MRC Secretariat referred to very high frequency and critically flow fluctuation in upper part of LMB (Chiang Saen to Vientiane), China provided additional information on the upstream hydropower dam operation in Dry Season Flow 2015.
Monthly Accumulated Rainfall Distribution over MB May: 0-150 mm (2014) : 0-60 mm (2015) The total acc. rainfall in 2015 is lower decreasing than 2014 during the Dry Season in May
Compared Regional Soil Moisture Condition-KBDI (2014-2015) May 2014 May 2015 May: 0-500 (2014) : 0-650 (2015) The total water holding capacity of soil moisture in 2015 is higher increasing than 2014 during the Dry Season in May (Source: http://webgms.iis.u-tokyo.ac.jp/dmews/gms/)
The condition of Inflow and Outflow Flows of the Tonle Sap Lake, in 2014 and 2015 Inflow Period Low outflow Very low inflow Low Outflow Low inflow Outflow Period High inflow It is confirmed the outflow into the Mekong River downstream in 2014 was Lower than long term average. 24
Month Average Volume (km3) Volume flow 2014 (km3) Percentage Jan 17588.79 19901.53 13% Feb 10008.49 11242.00 12% Mar 6199.40 6386.26 03% Apr 4703.67 4408.41-6% May 4360.11 3682.45-16% Jun 6273.89 4041.20-36% Jul 12850.93 12032.98-6% Aug 19934.40 21610.96 08% Sep 44052.83 40102.83-9% Oct 53237.86 39725.25-25% Nov 43155.67 30174.72-30% Dec 28833.42 21399.53-26% Very low Water Level from Nov. 2014 to April 2015
Flow Regulation Function Flood Peak Cut by storing water in the Flood plain Flow increase in dry season by releasing water from the Lake Channel flow Without flood plain Flood Peak cut Flood Mitigation volume by flood plain Channel flow Regulated by flood plain Flow increase effect Flow increase in dry season by flood plain Wet Season Dry Season
Conclusion in Dry Season 1. The flows from Chiang Sean to Vientiane were significantly fluctuated higher than the long term average; even though no rainfall contribution. Chaing Saen Nong Khai 2. The flow from Pakse to Kratie in December 2014 was higher than its long term average due to unseasonal rainfall in November 2014 and the influent inflows from upstream reaches. 3. Further sharing of hydrological Information in the region a comprehensive technical study is required. The process can be assessed in detail such the impact of upstream inflow and practical management and mitigation measures at downstream Pakse Kratie 27
Conclusion Tonle Sap Lake and Mekong Delta 1. The Tonle Sap Lake was not filled-in extensively by inflow from Mekong River and its catchment inflows during the wet season. Thus, the volume of the great lake was lower than 2014. it therefore leads to the low outflow which influent to flow condition below Phnom Penh. 2. Based on the low outflow from the great lake, It is expected that the flow in Mekong Delta during the early dry season of 2015 will be in the low flow condition, but the flow will be raised once it effects by rainfall in the areas. Chaing Saen Luang Prabang Vientiane Pakse Kratie 28
3. Future Change in Hydrology 2
Impact of Reservoir Operation in Monthly Changes Chaing Saen Vientaine 6000 12000 Flow, m3/s 5000 4000 3000 2000 1000 Chiang Saen2013 BL (85-93) Flow, m3/s 10000 Vietaine2013 8000 BL (85-93) 6000 4000 2000 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Pakse 30000 25000 Flow, m3/s 20000 15000 10000 Pakse2013 BL (85-93) 5000 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 3
Comments on the Impact flows With the 2 big Dams of the cascade Xiaowan and Nuozhadu (Int l RIVERS info), operated in 2010 and 2012 the downstream impact were observed as follows: The fluctuated water levels at Chiang Saen down to Vientiane The increased in water levels in Dry Season could reduce the exposed riverbank area for river bank gardens (vegetable gardens ) at downstream part (Chiang Khong.) The decreased of water levels/flows in Wet Season (fill storage and regulation reservoirs). This can be caused the reduction of floodplain area and flow of nutrients from flood waters. The deduction of sediment be cause cased river bank erosion also ect Saline intrusion into the Mekong Delta will increase with flow regimes that decrease wet-season flows.
Preliminary conclusion on Future Changes The Impact of river flow hydrology depends the flow phenomenon, including the Climate Change (rainfall pattern and high temperature), Hydropower Operation bases on national regulation. The Impact of reservoir operation can be resulted in: Decreased in Flood Peak Delay of Flood Peak Increased in Dry Season Flow Shorten of Flood Season Reduced downstream of flood duration in the floodplain and the Mekong Delta Therefore apply for Hydrological and Hydraulic Modelling combine with Climate Change Model are necessary The affect of Sediment load transport and Salinity Intrusion should be including for the next analyses.
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