Creating a sediment budget in a data poor context: an example from eastern indonesia

Abstract

Sediment budgets are useful in informing catchment management, however the resources and data required to create a sediment budget may be prohibitive, particularly in developing countries. This paper presents a multidisciplinary approach to an investigation of sediment sources and the creation of a first‐order sediment budget for a catchment in eastern ndonesia: a data‐poor region in the wet‐dry tropics with high sediment production rates and a population largely dependent on subsistence agriculture. The approach integrates results from geospatial analysis and key informant interviews and radionuclide tracers. Free software and imagery were used to demonstrate that geospatial analysis can be achieved without high costs. Surface soil erosion rates were mapped using the Revised Universal Soil Loss Equation, and subsoil sediment sources were digitised from high‐resolution imagery. Key informant interviews identified additional gully erosion, not detected through spatial analysis. Radionuclide tracers ¹³⁷s, ²¹⁰b_(ex) and ²³⁹u were used to determine the relative contributions of surface soil to sediment. The main sediment sources in the Kambaniru catchment were surface soils (31%), channel change (22%), gully erosion (8%), and landslides (1%), with an estimated annual sediment load of 1 440 000 t yr⁻¹ at the weir. This sediment budget showed subsoils were a major source of sediment, which contradicts assumptions that underpin Indonesian catchment management policies. The geospatial, interview and field methods were effective in identifying, mapping and quantifying subsoil sediment sources, and can readily be applied in areas where data are scarce and technical skills are low. Radionuclide tracers provide essential information but are expensive.

Key words:

• sediment budget
• sediment sources
• GIS
• radionuclides
• RUSLE
• mixed methods
• wet‐dry tropics
• Indonesia

Acknowledgements

The authors would like to thank AINSE Ltd for providing financial assistance (Award No. ALNGRA11073 and ALNSTU10084), and Australian Nuclear Science and Technology Organisation for analysis of radionuclide tracers, particularly David Child, Henk Heijnis, Michael Hotchkis and Atun Zawadzki. The first author acknowledges the support of a Prime Ministers Asia Australia Endeavour Award and an Australian Postgraduate Award. Thanks go to Umbu Ndjurumanna and Hanne Sang Ara for extensive field assistance, and we are grateful for the time and knowledge of interview respondents. All interviews were conducted with Charles Darwin University Human Research Ethics Committee approval #H12077. Guy Boggs provided invaluable advice over the course of the project. We acknowledge the contribution of Penny Wurm, Muhammad Nawaz and two anonymous reviewers for critical and constructive comments on the manuscript.

Additional information

Notes on contributors

Sarah E. Hobgen

Sarah E. Hobgen, Bronwyn A. Myers, Rohan P Fisher, Research Institute for Environment and Livelihoods, Charles Darwin University, Darwin 0909, Northern Territory, Australia

E‐mail: [email protected]; [email protected]; [email protected]

Robert J. Wasson

Robert J. Wasson, Institute of Water Policy, Lee Kuan Yew School of Public Policy, National University of Singapore, 469C Bukit Timah Road, Level 2, Wing A, Singapore 259772

E‐mail: [email protected]