The confluence of the Broadkill River, Canary Creek, and the Lewes-Rehoboth Canal with Delaware Bay at Roosevelt Inlet

DE - Charting the Course for Delaware's Waterway Management Using Geospatial Tools

The State of Delaware is responsible for maintaining most of its navigable waterways, from tributaries to the Delaware River and Bay to the Inland Bays along the state’s ocean coast. Dredging activities are often needed to maintain adequate depths of water in these waterways and can support beach sand replenishment and coastal hazard mitigation if strategically emplaced.

September 19, 2018

To optimize state funds to support maintenance of its coastal channels and beneficial use of sediment, the Department of Natural Resources and Environmental Control (DNREC) contracted us to develop a tool that supports a data-driven approach to prioritize dredge projects for its Shoreline and Waterway Management program.

We developed a tool to organize historical data to assist in visualization and assessment of waterways. Historical bathymetric survey data, navigational data, channel markers, centerlines, usage, and dredge history were researched. Once we assessed the data for each waterway, we developed a channel-specific survey plan that included details about the waterways, recommended survey lines for data acquisition, targeted depths based on usage and access, and nearby control monuments for use in future data acquisition efforts.

To catalogue and visualize the data, our team designed a geodatabase, parsing the data by channel. Most waterways in the geodatabase contain hydrographic sounding points with XYZ information collected over a period of several years by various sources. Other data layers include waterway centerlines, buoys and channel markers, federal navigational channel limits, and NOAA navigational charts. This geodatabase provided the first centralized repository of data for use by different groups within DNREC, improving their responsiveness to requests and inquiries as well as assisting their own survey group while in the field.

Geodatabase showing shoaling and scour within Indian River Bay Channel  

Using the survey plans and historical data, waterways were prioritized for hydrographic surveying based on age of existing data, waterway utilization and anticipated need for future dredging. Ten of the 37 total waterways DNREC maintains were identified for baseline data collection. The selected waterways included: Little Assawoman Bay, Assawoman Canal, Dirickson Creek, two sections of Indian River, Lewes-Rehoboth Canal, Little River, Mispillion River, MurderkillRiver and Rehoboth Bay Channel.

Once priority waterways were identified, we collected and added hydrographic survey data to the data holdings in the geodatabase. The geodatabase provides DNREC with a holistic view of the coastal waterways and allows for data-driven decision making to maximize the efficient use of available funding each year. At the same time, by having the data parsed by waterway, DNREC can also consider detailed assessments of a single channel or area to evaluate trends over time, facilitating identification of channel shifts, shoaling, scour, or other changes that may require additional monitoring or intervention.

The geodatabase now serves as a regional management tool for assessing the condition of channels to prioritize dredging of state-maintained and some federally authorized waterways in Delaware. It has also become an integral central data repository supporting field work and crews, coordination with other agencies, response to external data requests, performance calculations of estimated dredge volumes, development of channel designs, and response to constituents’ concerns regarding navigational challenges encountered in situ.

While in-person meetings are limited due to COVID-19, the tool is key in enabling quick access to data, resulting in rapid response and coordination between field and office staff for waterway management operations.As a result, the tool has improved efficiency and collaboration in DNREC’s waterway management operations state-wide.

Analysis for estimates of dredged volumes required to attain target depth in Dirickson Creek (figure from Sierra Davis, NOAA Coastal Management Fellow to DNREC)

See Coastal GeoTools 2021 - FINAL PROGRAM (February 8-11, 2021)

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