Update for November 18-24
Notable changes on the Mekong in the last week.
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SPOTLIGHT
Spotlight: Nuozhadu, the Mekong’s largest dam, is filling to new heights
Last week, China’s Nuozhadu Dam, the largest dam in the Mekong Basin,
surpassed all previously observed reservoir levels (since 2016 when the
MDM data archive starts). The previous highest observed reservoir level
was 809.6 meters on October 29, 2018. Last week, the reservoir reached
an estimated 810.6 meters and an estimated active storage of 11.69
billion cubic meters.
This is significant for a few reasons. First, drought in China caused
Nuozhadu to fill to much-lower than-normal wet season levels from
2021-2023. Second, typically at this time of year Nuozhadu begins to
release water for hydropower production – not fill its reservoir.
Wetness and precipitation conditions in the upper Mekong at the end of
this wet season have been favorable for filling reservoirs, and data
collected since 2022 suggests that the late wet season months are
getting wetter.
If this trend holds, then it’s possible for dam operators to wait to
fill reservoirs until the end of the wet season. Typically, dams fill
their reservoirs in the early wet season months much to the detriment of
the downstream floodpulse which naturally energizes during the wet
season months. A strong floodpulse promotes good fisheries and
agricultural production. A new pathway for smarter dam operations and
improved ecological conditions downstream is beginning to reveal itself,
but it is up to the Mekong’s dam operators to be convinced to follow
this path.
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Where is the water?
At the end of the wet season, we typically observe a mix of releases and
restrictions from dams throughout the Mekong. Last week was no
exception with releases observed at sixteen dams and restrictions
observed at seven dams. The largest releases came from Xiaowan (PRC, 722
million cubic meters), Jinghong (PRC, 144 million cubic meters), and
Nam Ngum 2 (LAO, 204 million cubic meters). The largest restrictions
came from Huangdeng (PRC, 162 million cubic meters), Nuozhadu (PRC, 332
million cubic meters), Nam Ngum 1 (LAO, 108 million cubic meters). This
led to a moderate net flow release of 573 million cubic meters of water
that will artificially raise the river level above natural flow
conditions.
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Reservoir Storage Over Time
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River Levels
River levels throughout the basin are generally near normal. Eyes on
Earth estimates that 26% of flow is missing at Chiang Saen, Thailand, as
a result of upstream dam restrictions.
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Chiang Saen Gauge
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Stung Treng Gauge
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Weather & Wetness
The upper basin in China experienced extreme wetness last week. The
center of the basin in much of Thailand and Laos has a mix of wet and
dry conditions. Most of Cambodia and Vietnam’s delta are experiencing
above normal wetness conditions.
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