Section 10 of the Rivers and Harbors Act of 1899 predates the Clean Water Act by three quarters of a century, and it is still doing work. On a navigable water it applies alongside Section 404, and it asks different questions.
Not legal advice. Navigability determinations and permit decisions belong to the Corps district with jurisdiction.
What it regulates
Section 10 requires authorisation for work or structures in, over, or under navigable waters of the United States, and for any activity that would excavate, fill, or alter the course, condition, or capacity of such a water.
Two differences from Section 404 matter:
The protected interest is navigation, not water quality. The question a reviewer is asking is whether the work obstructs, endangers, or interferes with navigation.
It catches things that place no fill. A pile driven into the bed, a pier, a mooring dolphin, an intake, an aerial cable crossing over the water, a floating structure — none of these need be a discharge of fill, and all can require Section 10 authorisation.
So a project can need Section 10 and not Section 404, need both, or need only 404 on a non-navigable water.
What “navigable” means here
Not what it means colloquially. Navigable waters of the United States for Section 10 purposes is a specific legal category, broadly covering waters that are currently used, have been used in the past, or are susceptible to use for interstate or foreign commerce, plus waters subject to the ebb and flow of the tide.
Two things follow:
Historical use counts. A river that carried commercial traffic a century ago and carries none today can still be navigable in the legal sense.
Tidal waters are included up to the head of tide, which brings in a great deal of coastal and estuarine water that would not be navigable in any practical sense.
The Corps district maintains determinations of navigability for waters in its area. Ask rather than assume.
How it works in practice
On a navigable water where the project also involves fill, the Corps generally processes both authorisations together. One application, one review, one decision covering both authorities. You will see the permit reference both statutes.
Nationwide permits are written to cover both where applicable, so a project fitting a general permit does not usually face two separate processes.
The place it matters is where Section 10 applies and Section 404 does not — work in a navigable water that places no fill. That is where a project team tracking only the Clean Water Act can miss the requirement entirely.
What Section 10 review looks at
Because the interest is navigation, the questions differ:
- Does the work obstruct the navigable channel, or reduce its usable width or depth?
- Is it a hazard, including to small craft?
- Does it need marking, lighting, or notice to mariners?
- Does it affect authorised federal projects — a maintained navigation channel, a federal breakwater, an anchorage?
- What are the effects on the water’s capacity or course?
The Corps also applies a broader public interest review, which considers navigation alongside conservation, economics, aesthetics, wetlands, fish and wildlife, flood hazards, recreation, water quality, and other factors.
Where this bites on erosion work
Berth and quay protection. Almost always navigable, and armor placed in a berth pocket occupies space in a working navigation area. Depth, extents, and the effect on declared depths all come into it. See scour at marine piles and dolphins.
Bridge protection on a navigable river. Both authorities apply. Armor around a pier in a navigation span raises the question of whether it encroaches on the channel.
Subsea pipelines and cables, and the protection placed over them, in navigable or tidal water. Anchoring, trawling, and charted depths are all navigation interests. See subsea free spans.
Coastal and estuarine bank protection below the head of tide, which is a much larger area than most people assume.
Any work near a federal navigation project. Maintained channels have their own constraints, and armor placed at or near the edge of one gets careful attention.
The practical questions to settle early
- Is this water navigable for Section 10 purposes? Ask the district.
- Is it tidal? If so, assume Section 10 until told otherwise.
- Is there a federal navigation project nearby, and what are its limits?
- What are the charted and declared depths, and does the work affect them?
- Does anything project above the bed into the water column?
- Will the finished work need marking or charting?
- Does the Coast Guard have an interest? Bridges over navigable waters and aids to navigation involve them separately.
Documentation it tends to require
Beyond the usual: plan and section drawings showing the work relative to the navigation channel, existing and proposed bed elevations, the relationship to any federal project, and often a survey establishing the channel limits.
For armor specifically, the extents and the finished elevation are the numbers a Section 10 reviewer cares about, because those determine whether the work encroaches or shoals.
Where to go next
- Permitting in-water erosion work for the overview
- Section 404 of the Clean Water Act for the fill authority
- State coastal zone approvals for the coastal layer
- Marine and ports and offshore and subsea for the applications
- Assembling the submittal package
- The permitting hub for the rest