Watershed Management Plans


watershed1A Watershed Management Plan is a process to develop a strategy to address flooding issues and protect and improve water quality and natural resources Interflow is on the forefront of using the latest tools and database technologies to organize data and to analyze watersheds efficiently and accurately. With experience evaluating over 20 watersheds throughout Florida, Interflow’s engineers and hydrologists are experts in solving a full array of complex water resource issues.

Typical steps in the watershed planning process are summarized below.


In this step in the watershed management plan, modelers identify and collect all of the relevant available information, e.g. as-built/construction plan information, existing stormwater inventory, existing models, gage information, high water marks, land use and soils mapping, field surveys, and photographs. This information is compiled into a database for the model development phase of the watershed management plan. Interflow is experienced in using the latest database structures to efficiently organize and analyze the existing data to develop a watershed model.

Phase 1
Phase 2
Phase 3
Phase 4



The watershed inventory leads into the development of the watershed model. The model development strategy is vital to having a model that is defensible and accurate. Therefore Interflow uses the latest science and technology to conceptualize the important flow processes and represent them accurately in the model setup. We have a number of modeling tools at our disposal, which allows us to tailor our approaches to each watershed’s unique characteristics and to the specific needs of our clients. GIS tools such as the ArcHydro toolset and in-house ArcGIS tools/methodologies allow us to develop model parameters accurately and efficiently. Along with the model development, the calibration of the model is crucial. Interflow’s team of experienced engineers are highly educated and well versed in calibrating watershed models in a multitude of modeling platforms.


Floodplain mapping is a very crucial step of a watershed management plan and can be a very time intensive process if an appropriate methodology to develop the floodplain is lacking. Interflow’s team of engineers has experience mapping floodplains with differing level of detail, as well as, numerous different types of floodplain models. Our engineers realize that different models require different methodologies to map the floodplain accurately and efficiently, e.g. the methodology to map the floodplain for a cross section based model may not efficiently map the floodplain for a node/link model. We have developed methodologies utilizing the tools within ArcGIS to accurately map floodplains through channel segments that should be interpolated from the upstream to the downstream in order to map the floodplain correctly.


floodroadThe floodplain analysis provides the information to easily identify flood prone areas for a watershed. The floodplain information is then used to characterize the levels of service provided by the existing stormwater infrastructure, based on the simulated depth and/or duration of flooding in streets and other improvements serviced by that infrastructure.

The areas that do not meet the desired level of service iare areas that will be evaluated during the Alternative Analysis phase of the watershed management plan.

ALTERNATIVE ANALYSISpropsedwatershedchart

The previous steps in the watershed management plan have identified the flood prone areas and the issues within the watershed. The next step is to analyze Best Management Practice Alternatives using the model as a planning tool to run “what if” scenarios. This is a process that involves identifying and evaluating the alternatives for solving flooding problems and water quality issues. Alternatives are evaluated based on cost effectiveness and other considerations such as public input and permitting considerations. Interflow’s team of engineers is experienced in solving complex water resource problems with innovative cost effective solutions.