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Introduction

This study tracks salt-marsh recovery across eleven tidal creeks on the lower estuary, focusing on how sediment supply and channel width shape the return of native cordgrass after levee removal. Field crews revisited each creek twice a season for three years, logging elevation, salinity and canopy cover at fixed stakes.

Data Methods

Transects were laid perpendicular to each creek and sampled with a one-metre quadrat every four metres. Elevation came from RTK survey; salinity from monthly grab samples read on a bench refractometer.

We interviewed twenty-two shellfish growers and two drainage districts about the trade-offs they weigh when a levee is breached on purpose. Most described a two-year window of uncertainty before mudflat elevation stabilised and their leases became workable again.

Growers in the upper reach reported the fastest turnaround, largely because the creek there carries a heavier suspended load in winter. Those on the seaward edge waited longer and lost a full harvest cycle in the process.

A smaller group had already restored parcels privately and served as informal advisors to neighbours, circulating hand-drawn maps of where the marsh took hold first.

Drainage district staff were more cautious. Their concern was not the marsh itself but the pumps behind it: a wider tidal prism changes how long the outfall gates stay shut on a spring tide, and nobody had modelled that at the creek scale before the first breach went in.

Two districts have since installed pressure loggers on the landward side and share the readings monthly with the growers' co-operative, which has quietly become the most reliable record we have.

Analysis

Recovery rate correlated most strongly with winter suspended-sediment load, then with distance to the nearest intact marsh seed bank. Channel width mattered less than expected once sediment supply was controlled for.

Creeks narrower than six metres trapped fine material quickly but drained poorly, producing patchy canopy with bare hollows that persisted into the third year of monitoring.

Conclusion

Where sediment is plentiful, marsh returns on its own within four seasons and planting adds little. Where it is scarce, thin-layer placement before the breach is the difference between a marsh and a mudflat.

We recommend that any future breach be paired with two winters of suspended-load sampling, and that funding for planting be released only after the second reading. The cost of waiting is one season; the cost of planting into a sediment-starved creek is the whole parcel.