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Tools for assessing hydrologic challenges and restoration potential of reservoir deltas: case studies from Southern California

Citation

Havstad, Emma (2020), Tools for assessing hydrologic challenges and restoration potential of reservoir deltas: case studies from Southern California, Dryad, Dataset, https://doi.org/10.7280/D10Q29

Abstract

California has lost nearly all its natural riparian ecosystems. Reservoir deltas represent an under-explored opportunity to restore these lost riparian forests across the west. However, flood magnitude, duration, frequency, timing, and rate of change are all modified along reservoir deltas, with varying impacts on key riparian species that support wildlife. I analyzed daily water elevation data from five reservoirs as case study sites and combined hydrologic and topographic data to delineate areas where riparian vegetation could become established. I compiled plant height data from a wide range of riparian restoration projects to evaluate the ability of riparian species to resist flood mortality. Finally, a case study illustrates challenges and lessons learned to guide future projects. Four of the five sites, while hydrologically highly modified, have portions of the drawdown zone where forest re-planting could be a feasible approach to expanding available habitat. Using these case studies, I developed a stepwise decision tree for integrating hydrologic data into site selection and restoration design. The framework illustrated in this report can be easily replicated to identify additional locations across the state where restoration has a higher likelihood of success and where additional data collection can further refine techniques.

Methods

Data from 23 River Partners restoration project sites in 8 counties across California were included in this dataset (Figure 4), representing a range of soil types and environmental conditions. Projects had been planted in 11 different years ranging from 2003 to 2018, representing a variety of precipitation and climate conditions. Plant propagules were either seed (ex., Quercus spp.), 18-inch cuttings buried to 12-inches (ex., Salix spp.), or one-gallon container plants. During the establishment phase, plants were maintained using horticultural restoration methods including highly aggressive mechanical or chemical weed control, and frequent supplemental watering using drip or flood irrigation based on soil conditions and evapotranspiration demand.  Height measurements were taken in 12 different years from 2005 to 2020, within 12 to 43 months after planting.

To select plants for measurement, we randomly established 20m x 50m monitoring plots in each restoration project at a rate of one plot per 5-20 acres. Plots were at least 10 meters from the project boundary, and oriented with the long axis (50m) facing north. All trees and shrubs within the plot were measured. Height was measured by placing a Stadia rod at the plant base and recording the tallest branch height.

Usage Notes

Please see attached ReadMe file.

Other datasets referenced here are publicly available:

Department of Water Resources. (2019). Daily SWP Reservoir Elevation and Storage Data. https://data.ca.gov/dataset/daily-swp-reservoir-elevation-and-storage-data [accessed on Nov 16, 2019]

U.S. Geological Survey. 2018. Digital Elevation Model - USGS National Map 3DEP Downloadable Data Collection: U.S. Geological Survey. https://portal.opentopography.org/usgsDataset?jobId=usgs1588274974053

Funding

River Partners