9 research outputs found
Quantification of surface water volume changes in the Mackenzie Delta using satellite multi-mission data
Quantification of surface water storage in extensive floodplains
and their dynamics are crucial for a better understanding of global
hydrological and biogeochemical cycles. In this study, we present estimates
of both surface water extent and storage combining multi-mission
remotely sensed observations and their temporal evolution over more than 15Â years
in the Mackenzie Delta. The Mackenzie Delta is located in the northwest of Canada and is the second largest delta in the Arctic Ocean. The delta
is frozen from October to May and the recurrent ice break-up provokes an
increase in the river's flows. Thus, this phenomenon causes intensive floods
along the delta every year, with dramatic environmental impacts. In this
study, the dynamics of surface water extent and volume are analysed from 2000
to 2015 by combining multi-satellite information from MODIS multispectral
images at 500 m spatial resolution and river stages derived from ERS-2
(1995–2003), ENVISAT (2002–2010) and SARAL (since 2013) altimetry data. The
surface water extent (permanent water and flooded area) peaked in June with
an area of 9600 km2 (±200 km2) on
average, representing approximately 70 % of the delta's total surface.\ud
Altimetry-based water levels exhibit annual amplitudes ranging from 4 m in
the downstream part to more than 10 m in the upstream part of the Mackenzie
Delta. A high overall correlation between the satellite-derived and in situ
water heights (R > 0.84) is found for the three altimetry missions.
Finally, using altimetry-based water levels and MODIS-derived surface water
extents, maps of interpolated water heights over the surface water extents
are produced. Results indicate a high variability of the water height
magnitude that can reach 10 m compared to the lowest water height in the
upstream part of the delta during the flood peak in June. Furthermore, the
total surface water volume is estimated and shows an annual variation of
approximately 8.5 km3 during the whole study period, with a maximum of
14.4 km3 observed in 2006. The good agreement between the total surface
water volume retrievals and in situ river discharges (R =  0.66) allows
for validation of this innovative multi-mission approach and highlights the high
potential to study the surface water extent dynamics
Initiation and evolution of knickpoints and their role in cut-and-fill processes in active submarine channels
Submarine channels are the main conduits and intermediate stores for sediment transport into the deep sea, including organics, pollutants, and microplastics. Key drivers of morphological change in channels are upstream-migrating knickpoints whose initiation has typically been linked to episodic processes such as avulsion, bend cutoff, and tectonics. The initiation of knickpoints in submarine channels has never been described, and questions remain about their evolution. Sedimentary and flow processes enabling the maintenance of such features in non-lithified substrates are also poorly documented. Repeated high-resolution multibeam bathymetry between 2012 and 2018 in the Capbreton submarine canyon (southeastern Bay of Biscay, offshore France) demonstrates that knickpoints can initiate autogenically at meander bends over annual to multi-annual time scales. Partial channel clogging at tight bends is shown to predate the development of new knickpoints. We describe this initiation process and show a detailed morphological evolution of knickpoints over time. The gradients of knickpoint headwalls are sustained and can grow over time as they migrate through headward erosion. This morphology, associated plunge pools, and/or development of enhanced downstream erosion are linked herein to the formation and maintenance of hydraulic jumps. These insights of autogenically driven, temporally high-frequency knickpoints reveal that cut-and-fill cycles with depths of multiple meters can be the norm in submarine systems
Quantification of surface water volume changes in the Mackenzie Delta using satellite multi-mission data
International audienceQuantification of surface water storage in extensive floodplains and their dynamics are crucial for a better understanding of global hydrological and biogeochemical cycles. In this study, we present estimates of both surface water extent and storage combining multi-mission remotely sensed observations and their temporal evolution over more than 15 years in the Mackenzie Delta. The Mackenzie Delta is located in the northwest of Canada and is the second largest delta in the Arctic Ocean. The delta is frozen from October to May and the recurrent ice break-up provokes an increase in the river's flows. Thus, this phenomenon causes intensive floods along the delta every year, with dramatic environmental impacts. In this study, the dynamics of surface water extent and volume are analysed from 2000 to 2015 by combining multi-satellite information from MODIS multispectral images at 500 m spatial resolution and river stages derived from ERS-2 (1995-2003), ENVISAT (2002-2010) and SARAL (since 2013) altimetry data. The surface water extent (permanent water and flooded area) peaked in June with an area of 9600 km2 (±200 km2) on average, representing approximately 70 % of the delta's total surface. Altimetry-based water levels exhibit annual amplitudes ranging from 4 m in the downstream part to more than 10 m in the upstream part of the Mackenzie Delta. A high overall correlation between the satellite-derived and in situ water heights (R > 0.84) is found for the three altimetry missions. Finally, using altimetry-based water levels and MODIS-derived surface water extents, maps of interpolated water heights over the surface water extents are produced. Results indicate a high variability of the water height magnitude that can reach 10 m compared to the lowest water height in the upstream part of the delta during the flood peak in June. Furthermore, the total surface water volume is estimated and shows an annual variation of approximately 8.5 km3 during the whole study period, with a maximum of 14.4 km3 observed in 2006. The good agreement between the total surface water volume retrievals and in situ river discharges (R= 0.66) allows for validation of this innovative multi-mission approach and highlights the high potential to study the surface water extent dynamics