Geomorphology of the fluvial-estuarine transition zone, lower Neuse River, North Carolina

The fluvial-estuarine transition zone (FETZ) of the Neuse River, North Carolina features a river corridor that conveys flow in a complex of active, backflooded, and high-flow channels, floodplain depressions, and wetlands. Hydrological connectivity among these occurs at median discharges and stages, with some connectivity at even lower stages. Water exchange can occur in any direction, and at high stages the complex effectively stores water within the valley bottom and eventually conveys it to the estuary along both slow and more rapid paths. The geomorphology of the FETZ is unique compared to the estuary, or to the fluvial reaches upstream. It has been shaped by Holocene and contemporary sea-level rise, as shown by signatures of the leading edge of encroaching backwater effects. The FETZ can accommodate extreme flows from upstream, and extraordinary storm surges from downstream (as illustrated by Hurricane Florence). In the lower Neuse-and in fluvial-to-estuary transitions of other coastal plain rivers-options for geomorphological adaptation are limited. Landscape slopes and relief are low, channels are close to base level, sediment inputs are low, and banks have high resistance relative to hydraulic forces. Limited potential exists for changes in channel depth, width, or lateral migration. Adaptations are dominated by the formation of multiple channels, water storage in wetlands and floodplain depressions, increased frequency of overbank flow (compared to upstream), and adjustments of roughness via vegetation, woody debris, multiple channels, and flow through wetlands.

Automated summary

The fluvial-estuarine transition zone (FETZ) of the Neuse River in North Carolina features a complex river corridor with unique geomorphological characteristics, shaped by Holocene and contemporary sea-level rise. It can accommodate extreme flows and storm surges, with limited options for geomorphological adaptation due to low landscape slopes and relief, close channels to base level, low sediment inputs, and high bank resistance. Adaptations in the FETZ include formation of multiple channels, water storage in wetlands and floodplain depressions, increased overbank flow frequency, and adjustments of roughness via vegetation and woody debris.