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

ISHIKAWA Yoshiharu Evaluating the effects of forest thinning on suspended sediment sources and transports in headwater catchments NAM Sooyoun ID: 10539703... In the plantation forest

Supervisor : Dr GOMI Takashi

Co- Supervisor : Dr ISHIKAWA Yoshiharu

Evaluating the effects of forest thinning

on suspended sediment sources and transports

in headwater catchments

NAM Sooyoun ID: 10539703

 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

- 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

 Importance on forest thinning

JAPAN

• Sources of picture : http://blog.daum.net/cbj8944/17051699 • Sources of picture : http://blog.daum.net/baekseokhandle/8004232

KOREA

 Forest management in headwater catchments

Suspended sediment* yield(SSY) can be accelerated

(* Sand, silt, and clay particles less than 2 mm in diameter; Gomi et al., 2005)

Thinning

 Hydrological process and sediment transport

Before timber harvesting

 Conceptual framework and objectives

For identifying effects on forest thinning

(1) Estimation SS transports using TSS in the thinning and

reference catchments

(2) Examination response of changes in Q-SSC during

the storm events

(3) Identification Cs-134 activity within headwater catchments

- Most of previous studies focused on clear and partial cuttings

- Although forest thinning had been extensively conducted,

effects of forest thinning were not investigated

I evaluated the effects of forest thinning

on suspended sediment sources and transports

in headwater catchments

 Two headwater catchments

 Forest thinning operation

Post-thinning

Pre-thinning Thinning catchment

During-thinning During-thinning Post-thinning

50 % Line thinning

 Forest thinning operation

skid trail

Machine for drugged timbers

 Paired catchment analysis

Before forest thinning

Gamma spectrometry

were determined by a gamma spectrometry

 Daily runoff and turbidity in the pre- and post-thinning periods

Pre-thinning Post-thinning

 Results of paired catchment analysis

TSS (Total SS yield) in the thinning catchment was

5 times greater than that in the reference catchment

 Hysteresis pattern in the pre-thinning period

 Hysteresis pattern in the post-thinning period

Stage 1

Stage 3

Stage 2

Anti-clockwise hysteresis indicated on SS sources occurred toward hillslope

 Percentage of hysteresis pattern in the pre- and thinning periods

post-Anti-clockwise hysteresis pattern was increased

from 0 to 18%

Thinning

 Summary of findings using SSC-Q hysteresis

 Cs-134 activity on the hillslope

 Greater amount of Cs134 activity was accumulated in

5 cm depth of soil

Integrated SS sampler

Liner sampler

 Amount of transported SS in stream channel

 Mean weight of integrated SS in the catchment

: Thinning (0.6 kg km-2) > Reference (0.1 kg km-2)

Integrated SS sampler

0 1 2

Reference catchment

Thinning catchment

 Radionuclide activity of transported SS

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 5 cm in soil depth

Reference catchment

Contribution of hillsolpe sediment

 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

nd clay particles less than 2 mm

in diameter; Gomi et al., 2005)

 Methods of soil erosion and suspended sediment

Parshall flume Water depth probe

Turbidity

Water sampler

Liner sampler

Soil sample Integrated SS sampler

Phillips et al (2000) “Time-integrated sampler”

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

(Mizugaki et al., 2008)

Transported SS

Mean 114% Mean 297%

>

Clearcut

Random thinning

Impacts of forest management on SS yields

SS yields in clearcut were greater than ones in random

thinning due to soil disturbance (Grant and Wolff,1991)

Clearcut

Random Thinning

Effects on skid trails with heavy machine on SS yields

SS yields by skid trail with heavy machine were greater than

ones with no skid trail with heavy machine (Meghan, 1972 )

Strip thinning

Random thinning

Skid trail Heavy machine

Strip thinning with skid trail and heavy machine

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

Infiltration

Recovered

Runoff Overland flow

 Hypothetical changes in SSY

Gomi et al., 2005