2017/11/16 UNESCO-JASTIP Joint Symposium on Intra-Regional Water Security andDisaster Management@SEDA Hotel, Quezon Phillipines, 15-16 November 2017

Rainfall-Runoff-Inundation Simulation forBasin-wide Flood Hazard Mapping at theBatanghari River in Sumatra, Indonesia
Disaster Prevention Research Institute, Kyoto Univ., Japan
Research Centre for Limnology, LIPI, Indonesia
Asia Pacific Centre for Ecohydrology (APCE), Indonesia
Graduate School of Advanced Integrated Studies (GSIS) in Human Survivability, Kyoto Univ., Japan

Takahiro Sayama1), Apip2), 3), Luki Subehi2)
Kodai Yamamoto1), Kaoru Takara1), 4)

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The Batanghari River Basin

Jambi City, March 15, 2017

The Batanghari River Basin (42,960 km2)

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A Regional Flood Hazard Map

Rainfall-Runoff-Inundation (RRI) ModelInput
Rainfall

1D Diffusion
in RiverSubsurface + Surface
Vertical Infiltration

OutputDischarge

DEM
W. LevelLand CoverInundation
Cross Sec.
2D Diffusion
on Land
Sayama, T. et al. Hydrological Sciences Journal, 2012.

RRI Model is freely available from ICHARM webpage.

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RRI Model Builder

RRI Model is freely available from ICHARM webpage.

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RRI Model Viewer

RRI Model is freely available from ICHARM webpage.

6Landscapes in the Batanghari RB
Tropical Forest in Sumatra

Tree Plantations

7Peatland Area in the Downstream

Land Cover and Hydrologic Cycle
Batanghari River Basin (42,960 km2), Sumatra, Indonesia
Upstream

Downstream
Frequent flooding areas, Wetland

Natural Forest
Peatland Area

Deforestation
Plantation

JambiSumatra

Drying wetland
Peatland fire

1. In Sumatra, 50 % of primary forest has been deforested in the last 25 years (1985-2009)
2. The deforestation has impacted to the increase of CO2 emission and change in thehydrologic cycle, causing flood and drought disasters, soil erosion and drying lands.
3. In the downstream part of the river basin, where large peatland exists, the change in river
flow regime as well as artificial drainage system for creating new farmland has dried the area,leading to frequent fire in the peatland area and haze issue.
9Land-cover land-use Change (LC)

Courtesy by Dr Apip

1990

1997

2005

2015

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Impact of Land Cover Change on Flooding• Based on BNPB data, during the period of 1995 until 2014,
the frequency of flooding in Jambi province had increased
steadily. The most probable reason was forest cover change
and the expansion of plantation crops (Tarigan, 2016).
• Deforestation increases the frequency of flooding.
• Scientific Questions- What are actual changes in hydrologic processes inducedby the land cover changes?
- In humid tropical rainforest / plantation croplands, what

is a dominant runoff process during storm events?
(overland flow / quick subsurface flow? )- How to assess the impact with hydrologic models?
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Three Conditions of Surface / Subsurface Flow in RRI
Surface / subsurface flow conditions(A) Only overland flow
(no infiltration loss, nosubsurface flow)(B) Vertical infiltration+ Infiltration excess
overland flow(C) Saturated subsurface+ Saturation excess overlandflow

Bedrock G.W.
in Mountainous Catchments

12In case of Japanese Forest
Soil depths: 60 – 100 cm
Underlain by granite bedrock(Kiryu Experimental Watershed)

Bedrock G.W.
in Mountainous Catchments
Peter Kienzler, ETH Zurich

13Chris Graham PhD thesis
14Thick Soil Depths in Tropical Climate
Forest mountainous hillslope

Soil depths = 5 m

Jambi

Sekancing Site16

Effects of Soil Depths on G.W. Recharge•

Use HYDRUS-1D: 1D Richards Equation Solver•

Soil Type: Sandy Clay Loam•

Upper Boundary: Atmospheric, Lower Boundary: ψ = 0 m
RainfallRainfallRainfallGroundGround3 Months

1-m Soil

ψ=0mTransient G.W.
G.W. Recharge

5-m Soil

ψ=0m
In case of 1-m Soil:・ High temporal variability in the G.W. recharge
・ With impermeable inclined bedrock,the recharged water becomes subsurface storm flow

G.W. Recharge

In case of 5-m Soil:・ Low temporal variability in the G.W. recharge
・ Hypothesis: no significant fluctuation in the17groundwater tableWell drilling and GW Monitoring
SK-3(0.13) m(2.77) m
HD: 8 mVD: 3 mhard bedrock(0.19) m(2.57 ) m layer
Position water level
HD: 10 m ( 6.16 ) m 2.43 m from thesurface
VD: 3 mSK-2

SK-1
0.05 mhard bedrock layer
Riv

HD: 10 m 5.71 m
VD: 4.7 m

5.57 m

( 5.91) m

Position water level4 m from thesurface

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SK-3

Monitored G.W. Depths

SK-2(2.57 ) m
( 6.16 ) m

SK-1
Riv

5.71 m

( 5.91) m

5.57 m19

SK-3

Monitored G.W. DepthsSK-2(2.57 ) m( 6.16 ) m

SK-1

The groundwater depth (SK-1) increases by
1.5 m within 10 minutes after the peak of rainfall

Riv5.71 m

( 5.91) m

5.57 m

16:00

17:00

18:00

19:00

20:00

21:00

22:00

The groundwater depth (SK-1) ismaintained after the rainfall stops

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Summary• Clear understanding of rainfall-runoff processes in humid tropical forest mountains isrequired for assessing the impact of land cover change on flooding.
• In our experimental hillslope, the soil depth at the slope foot was about 5 m and themountainous groundwater exist in the depths of 3 to 4 m.
• The groundwater table increase by about 1.5 m during some storm events and thendecrease gradually.
• Further studies are needed. Hope to develop a physically-sound element model
incorporated into the Rainfall-Runoff-Inundation (RRI) model.

New Hypothesis?
b) If the soil is characterized by clay,
the G.W. recharge may have high temporal variabilities

5-m Soilwith Claya) Controls of relatively
shallow soil In the upstream ?
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SK-3

Monitored G.W. Levels

SK-2(2.57 ) m( 6.16 ) mSK-1
Riv

5.71 m

( 5.91) m

5.57 m22

Research Projects• The Japan-ASEAN Science, Technology and Innovation Platform (JASTIP) funded by Japan
Science and Technology (JST)• Since FY2015• WP4: Disaster Research Group• Collaborative Research between DPRI, KU and Research Center for Limnology, LIPI
• MEXT KAKENHI (B)• Since FY2016• “Assessing the Impact of Deforestation in Tropical Forest in Sumatra, Indonesia, on
Hydrologic Cycle at the River Basin Scale including Lower Wetland Area” (PI: T.
Sayama)• TOUGOU Project: Integrated Research Program for Advancing Climate Models• Since FY2017• Area Theme D: Integrated Hazard Prediction (PI: Prof. Nakakita, KU)• Hazard Assessment in Asian and Pacific Countries and International Cooperation
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