Geographic variation in Puget Sound tidal channel planform geometry

• Tidal channel planform scaled with marsh area for 14 Puget Sound salt marshes
• Scaling exponents were uniform among salt marshes for 8 of 9 planform metrics
• Y-intercepts of the scaling relationships were geographically variable
• Channel size correlated positively with tidal range, negatively with wave energy
• Puget Sound salt marshes may already be suffering sea-level rise impacts

Tidal channels are central elements of salt marsh hydrodynamics, sediment dynamics, and habitat. To develop allometric models predicting the number and size of tidal channels that could develop following salt marsh restoration, channels were digitized from aerial photographs of Puget Sound river delta marshes. Salt marsh area was the independent variable for all dependent channel planform metrics. Tidal channel allometry showed similar scaling exponents for channel planform metrics throughout Puget Sound, simplifying comparisons between locations. Y-intercepts of allometric relationships showed geographic variation, which multiple-regression indicated was associated with tidal range and storm significant wave height. Channel size and complexity were positively related to tidal range and negatively related to wave height. Four case studies, each with paired regions of similar tidal range and contrasting wave environments, further indicated wave environment affected channel geometry. Wave-mediated sediment delivery may be the mechanism involved, with wave-sheltered areas experiencing relative sediment deficits, such that some salt marshes in Puget Sound are already suffering sea-level rise impacts that are reflected in their channel network geometry.