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2D Hydrodynamic Modeling for Evaluating Restoration Potential of a Vernal Pool Complex

  • Author(s): Fryjoff-Hung, Anna Franciska
  • Advisor(s): Viers, Joshua H
  • et al.
Abstract

Vernal pool landscapes are rare and highly modified. The Merced Vernal Pools and Grassland Reserve consists of 6,500 protected acres, preserving sensitive vernal pool habitat and organisms. The Reserve contains a number of modified stock ponds that have caused extensive alteration of the historic landscape to capture and retain water for longer periods than the seasonal wetland complexes dispersed throughout the site. Using a combination of empirical data and 2D hydrodynamic modeling, our project seeks to better understand how water moves throughout the UC Merced Vernal Pools and Grassland Reserve in order to evaluate the feasibility of potential hydrological restoration activities and develop a better understanding of potential management strategies. This study aims to assess the feasibility of restoring or enhancing existing natural vernal pool complexes through increased inundation by reconnecting historical channels via small alterations in previously modified terrain.

A 2D hydrodynamic model was developed using HEC-RAS rain-on-grid methodology to assess the restorative potential of a vernal pool complex at Avocet Pond in the Merced Vernal Pools and Grassland Reserve. In this currently modified system, levees disconnect natural channels and reroute overland flows into the stock pond which behaves as a reservoir, removing water from downstream landscape processes. Increased inundation to natural habitats benefits native vernal pool species whose life histories are integrally tied to finite and variable hydroperiods. Invasive plant and animal species may be reduced through the reduction of perennial stock pond hydroperiods and increased inundation and hydrologic connectivity of wetland features. Base case hydroecological conditions were established as the formative basis for evaluating the benefit of various restoration scenarios. Proposed restoration scenarios implemented simple terrain modifications such as small breaks in conveyance levees or notching stock pond berms. Model simulations suggest that historical flow paths can be reconnected through minimal terrain alteration resulting in increased inundation to wetlands and other downstream environments and reduction of overall stock pond inflows and hydroperiod. Results of this study will serve as a demonstration of landscape scale restoration of a vernal pool grassland habitat that has been altered through past land uses so that similar restoration assessment methodology can be implemented on other preserved lands in the state.

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