Process connectivity in a naturally prograding river delta

Abstract

River deltas are lowland systems that can display high hydrological connectivity. This connectivity can be structural (morphological connections), functional (control of fluxes), and process connectivity (information flow from system drivers to sinks). In this work, we quantify hydrological process connectivity in Wax Lake Delta, coastal Louisiana, by analyzing couplings among external drivers (discharge, tides, and wind) and water levels recorded at five islands and one channel over summer 2014. We quantify process connections with information theory, a branch of mathematics concerned with the communication of information. We represent process connections as a network; variables serve as network nodes and couplings as network links describing the strength, direction, and time scale of information flow. Comparing process connections at long (105 days) and short (10 days) time scales, we show that tides exhibit daily synchronization with water level, with decreasing strength from downstream to upstream, and that tides transfer information as tides transition from spring to neap. Discharge synchronizes with water level and the time scale of its information transfer compares well to physical travel times through the system, computed with a hydrodynamic model. Information transfer and physical transport show similar spatial patterns, although information transfer time scales are larger than physical travel times. Wind events associated with water level setup lead to increased process connectivity with highly variable information transfer time scales. We discuss the information theory results in the context of the hydrologic behavior of the delta, the role of vegetation as a connector/disconnector on islands, and the applicability of process networks as tools for delta modeling results.

How Important Is Connectivity for Surface Water Fluxes? A Generalized Expression for Flow Through Heterogeneous Landscapes

“…The fluvial biogeomorphic succession theory augments a growing focus on large-scale feedbacks in ecology and geosciences (De Lima et al, 2015;Meire et al, 2014;van de Koppel et al, 2015). In particular, there has been a call to better understand how connectivity (used here in the sense of structural connectivity, which describes the physical contiguity of landscape elements such as flow channels) impacts delivery of sediment and nutrients and associated feedbacks in low-gradient landscapes such as floodplains and deltas (Paola et al, 2011;Passalacqua, 2017;Sendrowski & Passalacqua, 2017) and in wastewater treatment wetlands (Sabokrouhiyeh et al, 2016 we quantify the sensitivity of large-scale flow to landscape spatial configuration and develop a relationship that predicts landscape-scale discharge from spatial configuration metrics, flow resistance properties, and water levels.…”

Temporal information partitioning: Characterizing synergy, uniqueness, and redundancy in interacting environmental variables

“…An additional aspect of ecohydrologic behavior is the capacity for many components to simultaneously influence overall system dynamics. In the example where wind speed and temperature are found to provide varying types and magnitudes of information to relative humidity during different time periods, the consideration of other variables such as wind direction [ Sendrowski and Passalacqua , ] or moisture conditions could explain some of these shifting properties. In a companion paper [ Goodwell and Kumar , ], we develop a network‐based approach that uses information partitioning to reveal the nature of time dependencies and ecohydrologic behaviors over the course of a growing season.…”

Connectivity as an emergent property of geomorphic systems

“…() provides an example based on multiple soil moisture datasets. Alternatively, statistical measures that characterize the frequency distributions of connectivity across scales can be used, as Ali and Roy () did for soil moisture and stormflow in a humid temperate forested catchment or Sendrowski and Passalacqua () did for hydrological processes on a delta influenced by river discharge, tides, and wind.…”