Lecture11 sediment in watershed (case study on effects of forest thinning on sediment)

Evaluating the effects of forest thinning on suspended sediment sources and transports in headwater catchments NAM Sooyoun ID: 10539703 Supervisor : Dr GOMI Takashi Co- Supervisor : Dr ISHIKAWA Yoshiharu  Forest management and plantation forest - The plantation forest is managed for the dominant part of sustainable timer production • Sources of picture : http://commons.wikimedia.org • Sources of picture : http://www.globalcarbonproject.org  Importance on forest thinning - 27 and 44% of forest in Korea and Japan are plantation forest In the plantation forest, forest thinning is essential for management of timber production JAPAN • Sources of picture : http://blog.daum.net/cbj8944/17051699 KOREA • Sources of picture : http://blog.daum.net/baekseokhandle/8004232  Forest management in headwater catchments Utilization of machine Thinning Soil disturbance Installation of skid trail Suspended sediment* yield(SSY) can be accelerated (* Sand, silt, and clay particles less than mm in diameter; Gomi et al., 2005)  Hydrological process and sediment transport Before timber harvesting After Catchment timber harvesting Overland flow Infiltration Infiltration  Conceptual framework and objectives - Most of previous studies focused on clear and partial cuttings - Although forest thinning had been extensively conducted, Radionuclide effects of forest thinning were not investigated tracer the effects of forest thinning I evaluated (He and Walling, 2003) For identifying effects on forest thinning on suspended sediment sources and transports Sources in headwater catchments (1) Estimation SS transports using TSS in the thinning and reference catchments (2) Examination response of changes in Q-SSC during the storm events SSC-Q hysteresis (3) Identification Cs-134 activity within headwater (Smith and Dragovich, 2009) catchments  Study site  Two headwater catchments K2 -17.1 (Thinning) K3 - 8.9 (Reference)  Area is covered by 40-50 yrs old Japanese cedar and cypress  Mean annual precipitation : 1,239 mm  Altitude range : 90∼290m  Dominant hillslope gradient : 20∼45°  Bedrock : Sedimentary rock  Forest thinning operation Thinning catchment Pre-thinning Post-thinning  Forest thinning operation skid trail Machine for drugged timbers 50 % Line thinning Pre-thinning During-thinning During-thinning Post-thinning Post-thinning  Paired catchment analysis Before forest thinning After forest thinning Thinning Thinned (K2) Reference (K3) Thinned (K2) Reference (K3)  Radionuclide activity of transported SS Low or no Cs-134 Contribution of hillsolpe sediment Hillslope Skid trails High Cs-134 Thinning catchment Reference catchment Dilution of radionuclide activity (by non contaminated soil) was occurred due to soil disturbance from skid trails installation and fine sediment located in more than cm in soil depth  Summary of findings  Total suspended sediment yield (TSS) in the thinning was times greater than that in the reference catchment  Sources of suspended (SS) in the post-thinning period were on skid trail with machine for drugged timbers These sources may affect in anti-clockwise hysteresis pattern  Suspended sediment in stream was transported through skid trails and disturbed soil surface  Summary of findings Thinning Skid trails Thank you for your attention Problem of SS in water resource management Suspended sediment* (SS) transport can be accelerated by soil disturbance (* Sand, silt, a Thinning Soil disturbance nd clay particles less than mm in diameter; Gomi et al., 2005) Increased SS can affect water resource management, par ticularly quality for drinking water (e.g., Ryan, 1991), industry (e.g., Ji et al., 2010), and agriculture (e.g., Matson et al,1997)  Methods of soil erosion and suspended sediment Water sampler Liner sampler Water depth probe Parshall flume Turbidity Integrated SS sampler Soil sample Phillips et al (2000) “Time-integrated sampler” 塩化ビニル製円筒管 ビニル製チューブ　内径4mm 本体寸法 側面図 内径4mm 正面図 採取された浮遊砂試料 内径 φ100 内径 φ100 L=1000 mm Water sample collection for storm event  Characteristic of radionuclides  Past nuclear experiments and accidents of nuclear power plants have related raionuclides to atmosphere (Rogowski and Tamura, 1970; Wakiyama et al., 2010)  Fallout radionuclides strongly attached to litter and surface soil on forested hillslope  Radionuclide tracers have been used identifying sediment sources in agricultural (e.g., Collins et al., 1998) and forested catchments (e.g., Mizugaki et al., 2007)  Examples for radionuclides tracers for SS sources This mixing diagram can explain transported SS is consisted by hillslope plots, truck trail, and stream bank Transported SS (Mizugaki et al., 2008) Impacts of forest management on SS yields > Mean 114% Random thinning Mean 297% Clearcut Clearcut Random Thinning SS yields in clearcut were greater than ones in random thinning due to soil disturbance (Grant and Wolff,1991) Effects on skid trails with heavy machine on SS yields > Mean 46% Mean 28 7% Heavy machine Skid trail No skid trail with hea Skid trail with vy machine heavy machine SS yields by skid trail with heavy machine were greater than ones with no skid trail with heavy machine (Meghan, 1972 ) Strip thinning with skid trail and heavy machine Random thinning Strip thinning Heavy machine Skid trail Strip thinning (> 50%) including installation of skid trail and utilization of heavy machine is conducted for timber investment by saving in working time Conceptual illustration for changes in hydrological process Unmanaged Managed Recovered Overland flow Runoff Overland flow Runoff Infiltration Infiltration Infiltration  Hypothetical changes in SSY Gomi et al., 2005 ... : Sedimentary rock  Forest thinning operation Thinning catchment Pre -thinning Post -thinning  Forest thinning operation skid trail Machine for drugged timbers 50 % Line thinning Pre -thinning. .. Pre -thinning During -thinning During -thinning Post -thinning Post -thinning  Paired catchment analysis Before forest thinning After forest thinning Thinning Thinned (K2) Reference (K3) Thinned (K2)... focused on clear and partial cuttings - Although forest thinning had been extensively conducted, Radionuclide effects of forest thinning were not investigated tracer the effects of forest thinning