Logjam controls on channel:floodplain interactions in wooded catchments and their role in the formation of multi-channel patterns

The role of wood in the formation and maintenance of complex dynamic floodplain surfaces is important andto date has received relatively limited attention compared to in-channel habitat processes. This paperexplores the role of logjams as important agents of channel:floodplain interaction. We draw on a specificcase study as well as examples from the literature to show that although the processes of interaction differ,the resulting dynamic floodplain patchwork is a common feature of rivers with logjams. In addition, wecontend that the presence of logjams is an important factor in the evolution and maintenance of multiplechannel patterns in both montane and lowland river environments. These observations have importantimplications for the definition of reference targets for river restoration.The specific results of this research show:1) The presence of a range of types of multiple channel network dissecting the floodplains of low orderchannels that are strongly associated with the presence of logjams.2) The relatively rapid formation of floodplain channels following logjam formation.3) The dynamic nature of logjams within headwater channels on both seasonal and annual timescales thatlead to a highly dynamic habitat mosaic on the floodplain surface.4) An increased frequency of overbank flooding and high rates of floodplain sediment accumulationupstream of logjams and along floodplain channel networks that create the complex topographyobserved in the case study forested floodplains

Basin-scale ice motion and deformation in the Weddell Sea during winter

Ice motion in the Weddell Sea is examined for the period 19 August (Day 232) to 12 October (Day 286) 1986 using the tracks of four Argos buoys deployed during the Winter Weddell Sea Project 1986 (WWSP 86). Two were SPRI/BAS buoys, launched in December 1985 and March 1986 in the south-east and north-west Weddell Sea. The others were part of a mesoscale array deployed in the Maud Rise area by H. Hoeber of the Meteorologisches Institut der Universität Hamburg, during the WWSP 86 cruise of FS Polarstern. The four buoys operated together for 44 d, comprising a basin-scale quadrilateral from which the differential kinematic parameters of divergence, vorticity, shear, and stretch were extracted, as well as the large-scale pattern of motion. It is found that most deformation episodes were associated with atmospheric forcing events

Periodic Motions in Weddell Sea Pack Ice

Position data from an Argos-tracked buoy deployed in the southern Weddell Sea in the austral summer of 1986 are analysed to determine important time-scales of variation of sea-ice motion in the seasonal sea-ice zone. Quality control and pre-processing of raw buoy data are discussed. Processed position data are subjected to time- and frequency-domain analyses. These highlight the importance of diurnal and semi-diurnal periodicities in the buoy motion. These preferred periodicities are associated with tidal forcing rather than wind forcing or inertial oscillations. Periodograms of the longitudinal component of buoy motion indicate that the power of the 24 h tidal component drops dramatically around day 130 in 1986. The possible causes of this are discussed and it is concluded that internal resistance within the sea-ice field may have increased at that time.</jats:p

Periodic motions in Weddell Sea pack ice

Position data from an Argos-tracked buoy deployed in the southern Weddell Sea in the austral summer of 1986 are analysed to determine important time-scales of variation of sea-ice motion in the seasonal sea-ice zone. Quality control and pre-processing of raw buoy data are discussed. Processed position data are subjected to time- and frequency-domain analyses. These highlight the importance of diurnal and semi-diurnal periodicities in the buoy motion. These preferred periodicities are associated with tidal forcing rather than wind forcing or inertial oscillations. Periodograms of the longitudinal component of buoy motion indicate that the power of the 24 h tidal component drops dramatically around day 130 in 1986. The possible causes of this are discussed and it is concluded that internal resistance within the sea-ice field may have increased at that time

Basin-Scale Ice Motion and Deformation in the Weddell Sea During Winter

Ice motion in the Weddell Sea is examined for the period 19 August (Day 232) to 12 October (Day 286) 1986 using the tracks of four Argos buoys deployed during the Winter Weddell Sea Project 1986 (WWSP 86). Two were SPRI/BAS buoys, launched in December 1985 and March 1986 in the south-east and north-west Weddell Sea. The others were part of a mesoscale array deployed in the Maud Rise area by H. Hoeber of the Meteorologisches Institut der Universität Hamburg, during the WWSP 86 cruise of FS Polarstern. The four buoys operated together for 44 d, comprising a basin-scale quadrilateral from which the differential kinematic parameters of divergence, vorticity, shear, and stretch were extracted, as well as the large-scale pattern of motion. It is found that most deformation episodes were associated with atmospheric forcing events.</jats:p