Indigenous technical knowledge for bank erosion and flood management

Transcription

1 2017 APEC Typhoon Symposium, May 2 4, 2017, GIS NTU Convention Center, Taipei Indigenous technical knowledge for bank erosion and flood management Hao Zhang 1) and Hajime Nakagawa 2) 1) Associate Professor, Natural Science Cluster, Research and Education Faculty, Kochi University 2) Professor and Director, Disaster Prevention Research Institute, Kyoto University *This research is funded by JST/JICA SATREPS Program on Disaster Prevention/Mitigation Measures against Floods and Storm Surges in Bangladesh

2 Indigenous knowledge Understandings, skills and philosophies developed by local communities with long histories and experiences of interaction with their natural surroundings Importance in the disaster risks clarification, disaster preparedness, disaster mitigation and disaster related policies/plans implementation Low cost, environment friendly Based on empiricism and in shortage of systematical validation

3 Bandalling Typical indigenous technical knowledge used in the Indian subcontinent for domestic navigation enhancement in low water periods, which may be simply described as a vertical screen mounted on a frame. Bank protection and new land creation. Bandalling immediately downstream of the Jamuna Bridge Unstable river bank New land July, 2008 July, 2009

4 July, 2009 Bandalling immediately upstream of the Jamuna Bridge July, 2008 Jan, July,

5 Severe bank erosion and potential flood Why Bandalling Revetment Traditional countermeasures Groyne Bandalling Traditional countermeasures

6 Sediment deposition experiments Unit: cm Ujigawa Open Laboratory, Kyoto Univ.

7 Suspended sediment deposition Revetment Groyne Effective in promotion of sediment deposition Bandalling structure

8 Flow velocity on water surface Groyne Bandalling structure

9 Flow velocity along longitudinal sections Groyne Bandalling structure

10 Flow velocity along transverse sections Groyne Bandalling structure

11 Impermeable Groynes Upstream Bandalling Structures Suspended sediment concentration Bay AB Impermeable Groynes Mainstream Bay BC Bandalling Structures Downstream

12 Suspended sediment concentration Groyne Bandalling structure

13 Movable bed experiments Unit: cm Ujigawa Open Laboratory, Kyoto Univ.

14 Erosion Deposition Deposition area is wider in non submerged case Deposition height is larger in submerged case Bed deformation No Bandalling structure Non submerged Submerged

15 Flow structure along longitudinal cross section Non submerged y=8cm Submerged y=8cm Downward overtopping flow is unique to the submerged case

16 Flow structure along transverse cross section Non submerged In front of A Behind A In front of B Submerged In front of A Behind A In front of B Flowseparationisseverer incaseofnon submerged case

17 Sediment concentration at z=4cm Non submerged Submerged

18 Sediment concentration along longitudinal cross section Non submerged Concentration decreasing from upstream bay to downstream bay Submerged Concentration in front of the structure> behind the structure

19 Conclusions Bandalling effective in promoting suspended sediment deposition along channel bank Upward flow passing the lower part of Bandalling structure provides sediment supply and keeps sediment in suspension Horizontal/vertical vortices result in sediment deposition and mainstream bay exchanges Downward flow is unique to submerged case Control of the upward/downward flow Ratio of the upper impermeable part to the lower permeable part and spacing between two consecutive structures

20 Thank you for your kind attention! Contact Dr. Zhang (Assoc. Prof.) for further information at *This research is funded by JST/JICA SATREPS Program on Disaster Prevention/Mitigation Measures against Floods and Storm Surges in Bangladesh