Welcome to Liberty Station
At Liberty Station in San Diego, the NTC Boat Channel is a tidal waterway shaped by both natural processes and human modification. Originally the mouth of the San Diego River, this area collected sediments carried downstream, forming deltas and wetlands along the edge of San Diego Bay. When the U.S. Navy built the Naval Training Center in the 1920s, the river was redirected and the boat channel was dredged through the old floodplain deposits. Today, the channel functions like a small estuary, where tidal waters from the bay mix with stormwater draining from the city. This EarthCache invites you to explore how tides, sediment, and contamination influence coastal waterways.
The Formation of the NTC Boat Channel
The channel sits on what was once the natural outlet of the San Diego River. Over thousands of years, floods carried sand, silt, and clay downstream, gradually building up a delta where the river met the bay. Tides from the Pacific Ocean pushed salt water inland, creating a shifting mix of freshwater and saltwater. In the 20th century, the Navy reshaped the landscape. A straight, wide waterway was cut through the river’s old deltaic sediments to create training areas for small craft. This excavation created the 54-acre boat channel, about 5,000 feet long and 500 to 800 feet wide.
Sediment Buildup & Contamination
The boat channel’s slow-moving water makes it a natural trap for fine sediments. Metals like copper, lead, and zinc, along with persistent pesticides such as chlordane and DDT, accumulated in the mud over decades of urban stormwater runoff and Navy use. In 2018, about 31,000 cubic yards of contaminated sediment were dredged from the channel to reduce ecological risk. This shows how tidal channels can serve as both important habitats and as long-term sinks for pollutants.
Erosion & Bank Stability
Erosion along the NTC Boat Channel varies depending on water flow, bank composition, and vegetation cover. Areas exposed to stronger tidal currents or wave action often show undercut banks, slumping soil, or exposed roots, while sections with dense vegetation or protective rip-rap remain more stable. Human modifications, such as straightening the channel or reinforcing certain banks, have altered natural erosion patterns, concentrating sediment deposition in some areas while preventing it in others. Observing these differences helps illustrate how natural processes and human interventions interact to shape the channel’s ongoing geomorphology.
To manage erosion, both natural features and human interventions play important roles. Some examples of natural erosion prevention observed along the channel include:
Natural Erosion Prevention Types:
- Dense vegetation along the banks, which stabilizes soil and absorbs wave energy
- Marshy areas and wetland plants that slow water flow and trap sediments
- Gravel or cobble deposits that protect banks from undercutting by currents
- Reef-building creatures, such as mussels or oysters, that slow currents
Human-Made Erosion Prevention Types:
- Rip-rap or rock armoring along vulnerable banks
- Reinforced or straightened channel sections to direct water flow
- Dredged and reshaped banks designed to minimize slumping
- Vegetation plantings specifically installed to stabilize soil
The Bay-to-Bay Dream
For nearly a century, San Diego planners have imagined extending the NTC Boat Channel into a full Bay-to-Bay connection, linking San Diego Bay to the San Diego River and Mission Bay. The idea first appeared in city plans in the 1920s and was revived in the 1970s. The canal would allow kayaks, canoes, and small boats to travel from one bay to the other, with parks and pathways along the route. Although it has never been built, partly due to environmental concerns about wetlands and endangered species, the concept highlights the intersection of geology, hydrology, and urban planning. If realized, it would permanently alter the way sediment and tides move through this part of San Diego.
Tasks for This EarthCache
To log this EarthCache, visit the site and answer the following questions. Send your answers via Geocaching or email.
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Include "NTC Boat Channel - Liberty Station - GCBC6DE" on the first line of your message.
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Look at the channel and its banks. Which features appear natural and which seem human-made? Based on your observations, would you consider this channel as primarily shaped by natural processes or human activity?
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Describe the water in front of you. Is it clear or murky? What does this indicate about the effectiveness of sediment cleanup programs?
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Examine the channel bank in front of you. Are there any signs of erosion? What natural and artificial features seem to be helping prevent erosion in this area?
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Imagine if this boat channel were extended to connect San Diego Bay with Mission Bay. Describe how this change might affect tidal flow, sediment movement, and deposition patterns. What potential problems might arise if the channel were extended in this way?
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In your log, attach a photo of yourself or a personal item at the posted coordinates with the channel in the background. (Note: photos predating the publication of this EarthCache are not accepted.)
Works Cited
https://www.sandiego.gov/sites/default/files/legacy/planning/community/profiles/midwaypacifichwycorridor/pdf/pebaytobay.pdf
https://media.defense.gov/2022/Mar/22/2002960990/-1/-1/0/SD201709_REMEDIAL_ACTION_IRSITE12_BOAT_CHANNEL_SEDIMENTS.PDF
https://www.waterboards.ca.gov/about_us/performance_report_1617/plan_assess/tmdl_outcomes/r9_navy_boatchannel_metals_pesticides.pdf
https://www.sandiegouniontribune.com/2022/09/27/once-tainted-by-ddt-navys-former-ntc-boat-channel-is-now-clean-and-ready-to-become-part-of-liberty-station/
https://www.waterboards.ca.gov/about_us/docs/performance_report/fy1718/rb9_ntc_boat_channel.pdf
https://en.wikipedia.org/wiki/Erosion_control
https://libertystation.com/
https://chatgpt.com/
AI Content Disclosure: Portions of the descriptive text on this page were created with the assistance of artificial intelligence tools. All content has been carefully reviewed, verified, and edited by the EarthCache owner to ensure accuracy and clarity.