The sand berm that separates Kaelepulu channel from the bay at Kailua Beach Park prevents the natural exchange of water that a normal estuary would have, and that the Kaelepulu Estuary had in the past.
There are two primary reasons why the berm should be opened on a monthly basis.
1. The City has a legal obligation to keep it open
The City signed a Drainage Agreement in 1963 that states that in return for allowing stormwater to flow into Kaelepulu Pond the City would keep the flow “open to the sea.” It’s a contract and they are not holding up their end of the agreement.
2. For the health of the estuary, the ecosystem, and the community
Regular openings will improve the health of the estuary and increase the ecosystem functions and services it provides to the community.
- Aquatic ecosystems are dependent upon flow to maintain equilibrium. Without flow stagnation occurs with the resultant decrease in oxygen, increase in anaerobic metabolic pathways used by microorganisms, increased bacterial counts, and decreased abundance of fish and invertebrates.
- Opening the berm facilitates the inflow of salt water along the bottom of the estuary and the outflow of fresher waters from the surface of the estuary. This “tractor tread” circulation greatly improves circulation and effective exchange, with resultant increase in salinity to the estuary as a whole.
- Increased salinity (hopefully averaging greater than 20 ppt) will allow existing (but rare) oysters in the system to effectively spawn and reestablish their once-abundant populations in the estuary. As one adult oyster filters about 0.5m^3 water every day, this should greatly improve water quality.
- Human pathogenic bacteria can typically survive in salinities up to about 15ppt as this is about equal to the “salinity” of human blood. Increasing the salinity to above 20ppt greatly reduces the survivability of human pathogenic bacteria.
- Opening the berm on a regular basis keeps the sand dune lower, decreasing the flood threat from unexpected storm events.
- Opening the berm on a regular monthly basis allows time for inflowing nutrients to be transformed into phytoplankton (~1 week) and then into zooplankton (another week) with huge loads of copepods and rotifers being consumed by juvenile fish in the estuary and/or flowing out into Kailua Bay.
Note: Only opening the berm when there is an active rainfall runoff event short-circuits this nutrient transformation process inherent in estuaries and merely pumps fine sediments and raw nutrients out into the Bay…not good. - Opening the berm on a regular monthly basis, particularly in the spring, allows eggs and larvae produced in the ocean to enter the estuary. In the past, when there have been significant openings during the spring, the following year there is an abundance of certain species. Sometimes in the past this has been sea-horses, papio, mullet, awa, or nehu.
- An open flow from the lake to the ocean will allow the large adult barracuda in the lake to migrate out to the deeper reef habitats they prefer.