Listed below are the members of HydroLogics team who are ready, willing and able to help clients with the toughest water resources management problems.

Daniel P. Sheer
Casey Caldwell
James Limbrunner
Tony Pulokas
Samuel Lebherz

Steven Nebiker
Dean Randall
Megan Rivera
Michael Sheer


Daniel P. Sheer, Ph.D., P.E.

Daniel P. Sheer is the founder and President Emeritus of HydroLogics.  Dr. Sheer has devoted his professional career to improving water management.  After receiving his Ph.D with honors from the Johns Hopkins University in 1974, he became the Planning Engineer, and then the Technical Director of the Interstate Commission on the Potomac River Basin.  In these capacities, he designed the technical work plan for the Washington Metropolitan Area 208 Plan (water quality management), and led the technical development effort that provided a long term water supply solution for the same region.  He was the first Director of CO-OP, the new institution designated to implement that plan.
In 1985 Dr. Sheer founded Water Resources Management, Inc., now renamed HydroLogics.  He has been directly involved in the majority of HydroLogics' projects, and was instrumental in the creation of the Southern Nevada Water Authority and the Kansas River Water Assurance District.  For the past decade, Dr. Sheer has been closely involved in planning and operations for the Everglades, Lake Okeechobee, the Everglades Agricultural Area and the Lower East Coast through contracts with the South Florida Water Management District.  He has directed the modeling of the Delaware, Susquehanna, and NYC water supply systems, and is currently engaged in modeling the Apalachicola-Chattahoochee-Flint and Alabama-Coosa-Tallapoosa Basins for the Atlanta Regional Commission and the South Saskatchewan River Basin in Alberta.
Dr. Sheer has done pioneering work in the development of water resources modeling technology and the use of Computer Aided Negotiation and Operations Exercises.  His work on HydroLogics' OASIS modeling system led to a U.S. Patent.  He has received Best Journal Paper citations from both AWWA and ASCE, was a founding member of the National Research Council's Water Science and Technology Board, and serves on the NRC's Committee to review the Florida Keys Carrying Capacity Study.

Dean Randall, Ph.D., P.E.

Dean Randall, Senior Engineer, has developed, written and used water resource-related models, making them represent reality, since 1974.  These models have taken into account many aspects of water resources management, including stream hydrology and hydraulics, floodplain analysis, ground water flow and contaminant transport, and storm water management.  At HydroLogics his modeling has all focused on operations of river basins, water supply systems, and hydropower systems.

Dr. Randall's specialty is using operations research techniques in writing models that water managers can use in making planning and operating decisions.  His early work at HydroLogics included building models for the Mid-Pacific Region (Sacramento) of the Bureau of Reclamation, the Southern Nevada supply system, the Eastern Irrigation District (Alberta), the Savannah River, and the Yellow River (China).  He led HydroLogics' original development of the modeling system, OASIS, which integrated optimization in the model.  He has been the lead modeler in many HydroLogics' projects; since 1998 these have nearly all focused on the application of OASIS.  These include several models in South Florida, models of several river basins (Delaware, Susquehanna, Kansas, Roanoke, and the Apalachicola-Chattahoochee-Flint system).  He has also used the Regional Simulation Model developed by the South Florida Water Management District.

Tony Pulokas, P.E.

Tony Pulokas, Senior Engineer, joined HydroLogics in 1996. Since then, he has been the primary developer of OASIS, HydroLogics' generalized modeling tool.   He has developed the Operations Control Language (OCL) from a novel idea into a powerful, fully featured tool in action.  He has also worked to make several existing computer models (such as groundwater, unsteady-flow, and water-quality models) integrate with OASIS.  Mr. Pulokas has been involved in the application of OASIS to studies of many water systems, including Alameda County Water District, Zone 7 Water District, the CVP/SWP, the Stanislaus River, and the New York City watershed.  One of the most demanding applications he worked on was a simulation of PG&E's hydroelectric system, which required the development of an efficient way of simulating real-world decision making that spans a long time range.

Before coming to HydroLogics, Mr. Pulokas was an intern at the Hydrologic Engineering Center of the U.S. Army Corps of Engineers, where he developed models of water supply reservoirs in Arizona using HEC-5 and a spreadsheet-based model of his own design.  As an intern at the Water Resources Division of the U.S. Geological Survey, he worked on the verification of an unsteady flow model (FEQ) being applied in DuPage County, Illinois.  For his master's thesis at the University of California-Davis, Mr. Pulokas analyzed the reliability of a reservoir system for the maintenance of a riparian vegetation corridor in Arizona, using an intermittent synthetic flow model.

Steven Nebiker, P.E.

Steven Nebiker, Vice President, joined HydroLogics in 2002. Prior to that, Mr. Nebiker spent most of his professional years with Malcolm Pirnie, Inc., an environmental engineering consulting firm.  His experience covers a broad range of water resources management issues, including water and wastewater treatability studies, water conservation, drought (risk) management, and facilities planning. Since joining HydroLogics, he has led development of a number of system-wide simulation and planning models, including those of the Yadkin and Cape Fear River Basins in North Carolina and the Rivanna River Basin in Virginia.  His efforts have centered on municipal water supply, including real-time drought management for the cities of Asheville, North Carolina and Charlottesville, Virginia.  He has also been involved in the modeling of hydropower operations, and is responsible for the day-to-day scheduling for Dominion Energy in the Roanoke River Basin.   

Megan Wiley Rivera, PhD

Megan Wiley Rivera, President, joined HydroLogics in 2005.  Dr. Rivera is adept at creating and enhancing OASIS models for a range of applications.  Her recent work includes simulating complex hydropower requirements and generation for nine dams on the Chattahoochee River, incorporating canal and floodplain hydraulics into an OASIS model of the Kissimmee Basin, and creating operating rules conditioned on forecasts of basin inflows that simultaneously increase benefits to endangered species and all other users.  

Prior to working at HydroLogics, Dr. Rivera was on the Civil Engineering faculty at The City College of New York.  Her research focused on environmental fluid mechanics with a variety of water quality and biological applications.  She developed and taught courses in Water Quality Modeling, Water Resources, and Fluid Mechanics based on innovative pedagogy.

Casey Caldwell, E.I.T.

Casey Caldwell, Water Resources Engineer, joined HydroLogics in 2008. Prior to that, Mr. Caldwell earned his Master’s degree in Environmental Engineering, with a focus on water resources management and modeling, from the University of North Carolina at Chapel Hill, and previously had worked for a small environmental engineering consulting firm in North Carolina.

Since joining HydroLogics, Mr. Caldwell has been involved in the development of several basin-wide simulation and forecast models using OASIS for the State of North Carolina, including the Neuse, Tar, and Broad Rivers. He has also been the lead modeler on numerous other projects, including a collaborative planning effort on the Duck River in Tennessee, where HydroLogics worked with stakeholders in the basin to assess water supply alternatives, as well as develop a drought management plan. Other project experience includes ongoing risk management support for various municipalities, including Rocky Mount and Raleigh in North Carolina; and the development of water supply models for a pilot program in Tennessee looking at regional solutions to capacity needs and drought mitigation.


James Limbrunner, PE, PhD

James Limbrunner, Senior Engineer, joined HydroLogics in 2008 and has developed an OASIS operations model for use in the hydropower industry.  His background includes experience in environmental site remediation and water supply development.  Dr. Limbrunner’s research interests include stormwater and nonpoint source pollution modeling and management.  His recent research has focused on developing systems formulations and optimization models for the management of nonpoint source pollution at the watershed scale.

A. Michael Sheer

A. Michael Sheer, Vice President, joined HydroLogics in 2005. With degrees in Biology and Agriculture he originally specialized in performance measure development with particular focus on ecological needs. After a 2-year break, he returned to the company in 2010 with a Master’s degree in Public Policy where his work focused on environmental policy. His thesis, available online, examined the political, social, economic, and environmental impacts of the recent expansion of Marcellus Shale natural gas drilling. At

HydroLogics his recent work has involved assisting in Computer Aided Dispute Resolution (CADRe) sessions and modeling the Saskatchewan River Basin for a variety of interested stakeholders. He also possesses an Advanced Training Certification in Conflict Management from the Center for International Development and Conflict Management.

Samuel Lebherz

Samuel Lebherz, Systems Modeler, joined Hydrologics in 2010 after receiving degrees in Environmental Science and Computer Science. He aids in the development of OASIS operations models, and programs custom tools to assist in model creation and use. Projects include a model output visualization tool that automates the process of loading performance measure visuals with model data, and a genetic algorithm wrapper for the OASIS software that tunes model parameters. Recently, Sam has been involved in the programming effort to build a new version of the OASIS GUI.



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