Dynamic river basins and hypsometric analyses: implications to land management and prioritization in Bohol, Central Philippines

ABSTRACT

The study presented a method of characterizing landform dynamics that integrates a divide stability metric and hypsometric analysis. Chi (χ) - a proxy for steady-state river channel elevation - indicated a drainage divide stability. Simultaneously, the hypsometric analysis provided information on a basin's geologic development stage and erosion proneness. The study used a 30 m SRTM digital elevation data, the DivideTool/TopoToolbox of MATLAB, and the SWAT model. The tool computed χ values following the stream network, enabled the selection of divide sections, extracted channel head's χ values, determined divide stability by predicting migration direction for unstable divides, and produced histograms of χ values for each divide section. Equal χ values at the channel heads of opposing river networks indicated a stable divide. In contrast, a difference in χ values suggested an unstable divide and a potential to migrate from low χ values towards the divide's high χ values side. The study proposed the mean χ difference (χ_md) metric to indicate the degree of divide mobility. Meanwhile, the SWAT model defined the basins and subbasins and set the hypsometric analysis parameters. Each subbasin's hypsometric integral (HI) was used to create a continuous surface of HI values. The combination of χ_md and HI analysis revealed nine subbasins with highly mobile divides and high erosional areas, identifying them as high-priority conservation zones. River basin characterization can utilize the new approach to target areas for location-specific land and water conservation measures and other developmental goals.

KEYWORDS:

• Drainage divide
• χ map
• hypsometric analysis
• geologic development
• land management and prioritization

Acknowledgments

The authors are grateful to the USGS-SRTM for the free DEM data (https://www.usgs.gov/centers/eros) and to the developers of DivideTools/TopoToolbox for the free and open-source program for the analysis of digital elevation models (https://topotoolbox.wordpress.com/topotoolbox/), and the Soil and Water Assessment Tool (SWAT)-watershed delineator, a free hydrologic model (https://swat.tamu.edu/). The corresponding author appreciates the scholarship program through the Engineering Research and Development for Technology - Department of Science and Technology (ERDT-DOST).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Engineering Research and Development for Technology - Department of Science and Technology (ERDT-DOST), Philippines: [Grant Number none].