Sediment Mitigation

When our watershed is degraded, bare soil results. Every time it rains, some of that soil washes downstream and ends up on coral reef. High sediment burdens create unhealthy coral, which in turn stresses the entire reef ecosystem.  In Pelekane Bay, where heavy silt run-off over the past few decades has been trapped, corals are buried in sediment, and the rich diversity of fish and invertebrates associated with the reef are absent.
Makeahua Stream

Sediment washing downstream after a heavy rain. Makeahua Stream, leading into Pelekane Bay.

On the Kawaihae watershed, which feeds into Pelekane Bay, we have been attacking the problem of erosion with a multi-pronged approach:

• Restoring native forest along two stream corridors:  to date, we have installed more than 35,000 native trees, shrubs, herbs and grasses. These plants will not only hold the soil, but will also capture and store rainfall.

• Control of feral goats: we constructed 18 miles of goat-proof fence around the lower 6,600 acre watershed of Pelekane Bay, and have removed the goats from the area.  This will allow vegetation to recover, and will decrease the amount of bare soil on the watershed.

KWP crew planting

The KWP crew planting on the Kawaihae watershed.

• Installation of sediment check dams and erosion control fabric: in the most severely damaged areas, we have constructed simple rock dams wrapped in plastic to slow down overland flows during storms.  The sediment being carried in the run-off can then settle out, preventing it from damaging downstream ocean environments.

Building a sediment check dam (L) and installing rolls of erosion control fabric (R).

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