Table 2 River Styles principles that support the understanding of fluvial geomorphology and guide sustainable river management in the Bislak Catchment and more widely in the Philippines

Capacity for adjustment

• Whether the river can adjust laterally, vertically, or both

• Where the river is likely to adjust, i.e. the spatial distribution of bank erosion

• Where the river is confined and less able (or unable) to adjust

• Where sediments will be deposited (aggrade) or eroded (degrade) in the channel

• Whether the channel can shift (migrate, avulse) and where this might occur

• Land-use planning (e.g., where not to build infrastructure or developments)

• Identification of hazardous buffer zones (flood- and erosion-risk)

• Providing ‘erodible corridors’, ‘space to move’, and/or ‘channel migration zones’ guided by a working with nature principle

• Strategic placement of necessary river control structures

River diversity

• Recognizing the diverse types of river, with various rates of adjustment, and behaviour

• Distinct characteristics and hydromorphological attributes

• Whether the reach is sensitive or resilient

• Which reaches (parts of the river) should be prioritized for catchment action planning (e.g., for conservation value), or to maintain sediment sources to prevent downstream degradation

• Different types of reach require different types of interventions

Identifying geomorphic units

• The presence of diverse geomorphic units signifies the types of river styles

• Indicates how the river behaves

• Differentiates erosional or depositional features

• Understanding where different habitats are located (e.g., fishing) and recreational areas

• Areas for sustainable gravel extraction

Pattern of rivers

• Whether the pattern is unique or similar to other patterns in the catchment

• Whether the boundaries between River Styles are gradual or distinct (abrupt)

• How sensitive different reaches are to pattern transitions due to changes in water or sediment supply, from upstream management decisions and climate change impacts (i.e., connectivity and offsite impacts)

Position in catchment and controls

• Whether the reach is a source zone, transfer zone or accumulation zone

• Whether the reach is situated in a low, moderate, or high energy environment

• Possible geologic and tectonic influences

• Policies for extractive activities

• Identification of geomorphic hazards (e.g., landslides, debris flows)

• Floodplain zonation

Tributary-trunk relationships (connectivity)

• Relative fluxes of water and sediment discharge from different parts of the catchment

• Downstream changes in grain size and thus roughness and water depth during high flows

• Land-use planning in vicinity of confluences

Know your catchment

• Regional settings and location influences the differences between catchments

• Locally appropriated management options, including socio-economic considerations and indigenous practices

Nested hierarchical approach

• Range of analyses and approaches that can be undertaken in different scales. Top-down approach on controls on character and behaviour while bottom-up approach on interpretation of the character and behaviour

• Coordination of management approaches from different local and national government agencies