Hydrologic Observatory: The Susquehanna River Basin (SRB) is the largest tributary to the Chesapeake Bay. Without this flow the estuary could not sustain its extraordinary diversity and productivity of aquatic life. The dilemma of our water-resource legacy is to balance the competing societal and environmental needs placed on the Susquehanna's freshwater resources. In 2002, Penn State took the leadership role in forming a consortium of scientists, policy makers, and stakeholders drawn from 30 universities as well as from federal and state agencies to design and implement the Susquehanna River Basin Hydrologic Observing System (SRBHOS) (www.srbhos.psu.edu). SRBHOS has been initiated to address "How do humans and climate impact the sustainability of the water resources within large river basins? What role do large rivers play in the global climate system?". Overview of Research: This proposed research plan will advance the SRBHOS science agenda by investigating the three research themes: (1) Assessment of the significance of the regional water table, its role as a lower boundary condition to soil moisture, and the impact of water table status on hydrologic extremes (floods, droughts). We propose to develop the concept of a subsurface boundary layer (SBL), which we define as the depth beneath the land surface for which the local atmosphere and land-surface processes will affect the local flow of groundwater to streams. An algorithm will be developed to map the SBL using the SRBHOS digital data. (2) Integrated models that include vegetation water and energy dynamics will improve hydrologic forecasts at the basin-scale and are critical to resolving the relative importance of recharge to the shallow groundwater table and transpiration of soil moisture (3) Macropores have a significant affect on the hydroclimatic performance of watersheds during wet and dry cycles. We intend to develop new parameterization strategies to correct the regional soils database for macropore flow based on the Shale Hills testbed. Currently soil classification only considers "matrix" properties (conductivity and water holding capacity). Finally, this research will attempt to demonstrate how a unification of modeling, existing digital data, and new data collection strategies will advance our understanding of river basin water resources and support the design of hydrologic observatories. Intellectual Merit: The present proposal will unify early SRBHOS science efforts and address how a physical model and a-priori data can be used to promote scientific collaborations that: (1) will aid the SRBHOS community in formulating hypotheses and potential scenarios for hydrologic change within the basin; (2) will promote the development of new data-driven algorithms that enhance our ability to represent and predict water cycle dynamics; and (3) that will support a scientifically-based design for the future observatory's sensor network. Addressing these issues will aid SRBHOS scientists in assessing climate and human feedbacks across multiple scales as well as physiographical and ecological conditions. The tools developed in this research will contribute to improving our understanding of the roles of terrain, ecology, and geology in partitioning water and energy across the complex environmental systems that make up the SRB. Broader Impacts: This proposed research will be disseminated broadly to the academic, state, and federal SRBHOS partners through a Susquehanna Data and Modeling Symposium, which will be organized by the PIs in conjunction with the Chesapeake Research Consortium. Funds requested in this proposal for the symposium will be leveraged with others sources of funding to maximize our ability to invite national leaders in river basin modeling and data systems to review the proposed tools developed in this research as well as contribute their own expertise and tools to the SRBHOS community modeling effort. All software and data resources developed in this project are dedicated to the "open source" framework and shared through the Chesapeake Community Modeling Program. Additionally, this research effort will exploit basin-wide collaborations such as the currently pending Susquehanna REU to promote undergraduate education and to recruit demographically and geographically diverse students currently underrepresented in hydrologic science.
