河流改道-地理边界条件与其它因素解析课件.ppt

1、Louisianas Coastal Land Loss:A Regional Geology ProblemMississippi Delta Land Loss and GainUSGS Crustal Downwarping Compaction-Dewatering of Young Deposits Faulting Decreasing Sediment Supply-Increasing AccommodationKey Geologic Factors in Land LossPost-Glacial Alluvium and Deltaic Sediments=60.500

2、km2Post-Glacial Alluvium and Deltaic Sediments=60.500 km2Based on 325 USACE boreholes from Blum et al.(2008)braided stream depositsLower Mississippi Valley and DeltaMagnitude of Post-Glacial DepositionTotal storage=1860-2300 km3 or 2790-3450 BT of sedimentStorage rate=230-290 MT/yr over 12,000 yr po

3、st-glacial period Balize Delta 100 m ThickData courtesy of USGS Baton RougeData courtesy of USGS Baton Rouge230-290 MT/yrSatelliteobservationsTide-gaugeobservationsfrom IPCC 2007 1mm/yr1.7 2.0 mm/yr3.0 mm/yrCoastal Plain GPS Vertical VelocitiesCoastal Plain ElevationsProjected Submergence:2000 vs 21

4、00Projected future land loss of 10,500-13,500 km2 The Louisiana Coast in 2100?New accommodation 12-16 km3(Requires 18-24 BT to fill accommodation)Projected future land loss of 10,500-13,500 km2 1400-1800 km2with 50%ofsedimentload The Louisiana Coast in 2100?Fundamental Questions:River Diversions How

5、 are the sediments partitioned within the coastal-shelf system?What is the sediment retention capability in the delta and adjacent marshland?What are the important processes linked to sediment transport to the delta-marsh-offshore?Primary Physical Process Data Collection SitesDelta ADCPBig Hog Bayou

6、 Cross-Channel ADCP SitePartitioning of Discharge:Wax Lake DeltaHurricane IsaacDelta Side-Looking ADCPTropical Storm LeeSeptember 4,2011Primary Physical Process Data Collection SitesDelta ADCPWax Lake Outlet ADCP,Current Speed(cm/s)Marsh Accretion Study SiteMarsh Grass Pushed Over by Water from Big

7、Hog BayouSediment AccretionRising Flood and Cold Fronts Form Synergistic Sediment Delivery ProcessesCold Front Modulation of Sediment Transport Prefrontal:Onshore Winds Water Level Set-Up Onshore Sediment Transport Postfrontal:Offshore Winds Water Level Set-Down Offshore Sediment TransportBig Hog Ba

8、you,Side-Looking ADCP,Current Speed(cm/s)Water Level Demeaned and Offset with Wind SpeedPrefrontal ConditionsPostfrontal ConditionsProject Results Suggest:Placement of River Diversions in Landward Parts of Interdistributary Basins Will Maximize Sediment Retention Through Landward Suspended Sediment Transport by Cold-Front-Related Processes.