Effects of the Suwannee River Sill on the - University of Florida

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					 Effects of the Suwannee River Sill on the
            Okefenokee Swamp
        Hydrological Environment

 Cynthia S. Loftin USGS-BRD Maine Cooperative
         Fish and Wildlife Research Unit
            University of Maine, Orono

Wiley M. Kitchens USGS-BRD Florida Cooperative
         Fish and Wildlife Research Unit
         University of Florida, Gainesville
         Georgia

                Atlanta

                   Macon
                             Savannah



  Tallahassee              Jacksonville



     Okefenokee
National Wildlife Refuge
    Project Objective:
Has the Suwannee River sill
 affected the Okefenokee
   Swamp hydrological
environment and vegetation
       distributions?
       Water Control
        Structures




                        Main Channel
                       Suwannee River
Sill
                                Aquatic Prairie



Forested Swamp              Herbaceous Prairie




Smilax spp. and shrubs   Upland Pine Forest
                                  Sill Area
                             Average Conditions




                 Sill Area, Dry Conditions


 Main Channel,
Suwannee River
Sill Ditch, Dry Conditions
Processes Affecting the Okefenokee Landscape
        and the Scale of those Effects
                 1cm   1m           1km              1000km

            4                                                         10,000 years
                                               landscape
            3                                                         1000 years
                                            forest
            2                                            Drought      100 years
                          patch stand
                                            Logging
Duration of  1                                                        10 years
Disturbance 0             canopy
or Landscape       leaf                     Hydrology Change          Year
Component -1                     Fire                                 Month
(Log Years) -2                                           Hurricanes
                                                                      Day
            -3                      Thunderstorms                     Hour
            -4
            -5
                                                                      Minute
            -6
                  -4        -2          0            2       4

                          Space (Log Kilometers)
Hydrological         Physical         Vegetation
 Features          Environment         History


           Species’
                            Manipulative
         Hydrological
                             Processes
         Environment

                  Comparisons:
                 HYDRO-MODEL
                  Map Overlays
                 Species’ Models


     Landscape Patterns    Suwannee Sill
       and Processes         Effects
                       Hydrological Features
                             Weather,
                            Water Level,
                               Flow



Physical Environment
    Topography,
   Peat Thickness
Vegetation          1952 BW
                     Photos
 History


      Pre-logging
        Surveys

                    1990 Imagery




     1977 CIR
      Photos
        Species’
Hydrological Environments
 Manipulative Processes
1891-1897   Suwannee Canal
1889-1942   Logging
1950s       Peat Mining
1960-1962   Suwannee Sill
            Construction
              Flow Features and Directions
               During Average Conditions




Suwannee
 River Sill
                       Daily Water Depths
                    in Swamp Basins (1993)
      2.25

      1.75           West

Water 1.25
Depth                East                Central
 (m) 0.75
                Northeast
      0.25
                Southeast
      -0.25
              JAN   MAR     MAY   JULY   SEPT      NOV
                              Month
Swamp Topographic
   Surface and
 Hydrologic Basins
    HYDRO-MODEL Steps
       Water Depth
         + Rain
         + Inflow
          - Outflow
           - Evapotranspiration
+   Ground Surface Elevation/Roughness
    Flow Direction Calculation
    Amount of Water to Move
    Water Movement
                                   Model Simulations
                  2.25
                          Northeast
                  1.75

                  1.25

                  0.75
Water Depth (m)




                  0.25                                         no sill
                                                               with sill
                  -0.25
                                                               no outflow
                    2.5     West                               75% ET
                                                               150% ET
                     2

                    1.5

                     1

                    0.5

                     0
                          1980     1985          1990   1994
                                          Year
          Annual Average Water Depth
                  1941-1995


        SCFSP


Water
Depth
 (m)

        SCRA




                    Year
 Areas Affected by
Model Manipulations
                   Inflow
                  Outflow
                               ET
                     Sill




                       ET
               Sill (upper basin)


             Outflow
               ET       ET
                   Areas Affected by Sill Operation

        Extended hydroperiod
            in high water
             conditions


                                                   Flow direction
Extended hydroperiod                                 reversal in
     in low water                                 very high water
      conditions                                  level conditions

      Reduced
     hydroperiod




                    Increased outflow in
                      very high water
                      level conditions
            70                                             Vegetation Composition
            60                                                  of Okefenokee
            50                                             National Wildlife Refuge
  Percent



            40                                                    1890-1990
            30
            20
                                                                  Upland Pine
            10                                                    Wet Forest
            0                                                     Shrub
                 1890   1952          1977       1990             Prairie
                           Year


                                                        Vegetation Type in 1990
                               Vegetation Type   Sill    South-    East-             North-
Regional Comparison                in 1952       Area     west    Central   North     east
   of Changes in
 Vegetation Types,               Wet Forest      WF       WF, S    WF, S        WF    WF
                                   (WF)
  Before and After                 Shrub         WF       S, WF      S          WF   S, WF
  Sill Construction                 (S)
                                   Prairie       WF         S        S          WF     S
                                    (P)
            Proportion and Size of Wildfires by 5-Year Intervals
                               (1855-1993)
                 60

                 50

                 40

                 30

                 20

                 10

                  0

             210000
             180000
             150000
Area (ha)
             120000
                                            Sill Construction
              90000
              60000
              30000
                  0
                      ~
                      ~
                   55

                   25

                   35

                   45

                   55

                   65

                   75

                   85

                   95
                 18

                 19

                 19

                 19

                 19

                 19

                 19

                 19

                 19

                              5-Year Interval
Vegetation Succession in Okefenokee Swamp

                        Prairie
                                  Prairie-Shrub-Swamp
   Prairie-
   Shrub-          Shrub-Swamp
   Cypress


  Shrub-Cypress-Swamp                  Bay-Shrub-Swamp



  Cypress-
     Bay-       Mixed Blackgum Swamp
  Blackgum                               Bay-Swamp
   Swamp
                                  no fire
                                  moderate fire
                                  severe fire + logging
                                  1977      1990
           Summary Points
• The Suwannee River sill is increasing
  flooding depth and duration in 18% of
  the refuge, primarily during periods of
  abundant precipitation.
• Although fire management may be
  affecting fire distributions, the sill has
  little effect of the swamp fire regime.
           Summary Points
              (continued)

• The observed changes result from
  logging, fire management, hydrologic
  manipulations, and vegetation
  succession.
• The role of these processes as the
  primary driver of change is influenced
  by the location within the swamp.
     Acknowledgements
Okefenokee National Wildlife Refuge,
    USFWS-Region 4, USGS-BRD,
N. Ansay, J. Aufmuth, J. Brookshire,
 C. Depkin, D. Evenson, J. Kitchens,
     J. Loftin, D. O’Neill, P. Owen,
L. Pearlstine, B. Rasberry, K. Williges

				
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