Connectivity & Socio-Hydrogemorphic Vulnerability of the Oregon Coast


Transdisciplinary Co-Authors: Jasmine King, Rosemary Pazdral, & Emerson Web

Primary Questions:

  1. Do hydrological regimes influence the morphology of estuaries?

  2. How do social and natural sources of sediment production change over time?

  3. How can vulnerability, especially related to coastal flooding, be defined in watersheds, estuaries, and Oregon coastal communities? How do the vulnerabilities in these individual systems sum to landscape-wide vulnerability?

Motivation: Human and natural systems are highly connected along the Oregon coast. The ocean, estuaries, and watersheds provide essential ecosystem services to coastal communities, including flood protection, water availability, and economic opportunities. Industries that utilize the local natural resources, namely timber, fishing, and recreation, provide the primary sources of revenue in the region. Due to the interconnectedness of coastal Oregon socio-ecological systems, impacts of climate and land-use changes on the conditions of natural systems are also likely to disrupt local social systems. Human reliance on ecosystem services may place coastal communities in vulnerable states via physical, social, and economic avenues. From a hydrogeomorphic standpoint, small, mountainous rivers drain the Oregon Coast Range, transporting sediment to estuaries. Within estuaries, a fraction of this material accumulates in coastal wetlands, which provide critical flood protection for adjacent communities. Thus, variability in streamflow regimes likely influences estuarine morphology but in poorly understood ways. From a social standpoint, human land-use practices and policy decision-making that have led to changing logging practices, diking, culverts, and restoration projects also had substantial impacts on freshwater conditions and estuarine morphology, but relationships need to be elucidated.

Investigative Approach: We present a pilot study comparing three coastal Oregon watersheds with varying responses to climate and land-use changes. The Nehalem, Alsea, and Coquille watersheds were selected as study locations to determine the relative importance of different drivers of socio-ecological vulnerability, as these systems span the Oregon coast and exhibit key differences in estuarine and watershed morphology, and land-use history. Changes in salt marsh morphology over the last century are characterized by both vertical (measured by excess 210Pb and a Bayesian model) and horizontal (measured by aerial photograph analysis) sediment accumulation rates. Chemical characteristics (e.g., carbon, titanium, bromine) are analyzed through time to approximate sediment source. We characterize the hydrological regimes of each watershed using three rate-of-change metrics: flashiness, streamflow recession, and dynamic basin storage. The hydrological regime analysis relies on spatially- and temporally- explicit precipitation and hydrological data. Additionally, we are characterizing and comparing each watershed based on hydrogeomorphic parameters, which are first-order controls on the storage-discharge relationship. These include basin size, predominant basin lithology, and the spatial distribution of topographical features (i.e., slope, gradient, elevation, drainage density, and valley floodplain area).

To connect changes with estuarine and watershed morphology with human land use practices, a sample of Oregon statewide forest and coastal policies, U.S. federal environmental policies, and local policies are identified and characterized chronologically. Additionally, histories of land-use practices such as logging, splash damming, and diking have been characterized alongside policy histories to provide an in-depth picture of how land-use practices have changed over the last century. To describe the effects of both human and natural system changes on coastal communities, a vulnerability index is constructed using American Community Survey data for Census Subdivisions situated within the Alsea, Nehalem, and Coquille systems.

Connectivity between the estuaries and watersheds for Nehlaem, Alsea, and Coquille will be assessed by: 1) comparison of estuarine characteristics with hydrologic regimes, and 2) time series comparisons between salt marsh sediment accumulation and changes in discharge record and the histories of human land-use and policies. Vulnerability of each system will be assessed by characterizing the physical vulnerability within the watersheds and estuaries, and the socio-economic vulnerability within the coastal communities of each system.    

Status: My team members and I completed this research as part of our fellowships in the National Science Foundation Research Traineeship program in Risk and Uncertainty Quantification in Marine Systems. We presented this research at the AGU Fall Meeting 2020 (virtually)