Because of a lack of flow in many streams due to water diversion or habitat change, three problems have risen: The lack of rapids lessens airration, the slower water speed raises water temperatures and also allows faster sediment buildup in possible breeding grounds for certain fish.

Most streams in hawaii, because of the above reasons do not flow regularly into the ocean like they normally would. A slower water flow means that sand banks always block the entrance of the river/ stream mouth to the ocean and the only time that they open is when a big rain comes. When this happens, sediment that would have normally been flushed out slowly comes out all at once, blanketing and killing nearby reefs.

Many native amphidromous fish species are not adapted to restricted water flows, higher temperatures and low oxygen levels, causing them to not complete their life cycle of returning from the ocean to streams and rivers.

In some local streams, large-diameter pipes have been installed to accomodate for the constant sand banks, but they themselves, if not cleared frequently, can be themselves clogged as fast as overnight.

My idea: Large-diameter pipes by themselves leave maintenance problems, but install a pressure or tidal activated valve and it will clean itself. Even with a tidal difference of only two feet, enough pressure can provide a rush of water flow that would serve different purposes:

The sudden rush of water in and out would: airrate the incoming water, clear the pipe of sand and debris, provide a more constant unsettling of sediment, allow for amphidromous fish life cycles.

It's a large pipe with a valve activated by tides or pressure that connects locked streams to the ocean. It is self-cleaning and improves stream conditions for native wildlife.

When enough pressure difference is detected or tides are determined, the valve opens and a small tidal wave is created. it's like a laxative for a constipated stream.
-- twitch, Nov 20 2006

Totally not seeing how tides (a seawater phenomenon) will help freshwater streams. You've either got to install pumps, which would risk harming the fish populations, as well as get clogged in turn, or use seawater, which would kill many of the fish outright, as well as be impractical above sea level.

Some dams in the mainland US are using artificial flooding to mimic the seasonal floods which carry silt downstream, and refresh local water habitats. I wonder if that is what you are groping towards?
-- DrCurry, Nov 20 2006


Streams were originally affected by tidal swells before roads and bridges and water diversions were installed. It is just a restoration of a natural occurance. The native amphidromous fish are tolerant of both full salt and fresh water. They are actually dependant on water flow cycles: if they don't detect water flow cycles that can take the eggs out to sea, they won't mate.

It was also my observation of the recent Japan earthquake which caused 3 foot tidal swells, sucking water in and out of the stream.

You don't have to intall pumps, you are just waiting for sea level height differences to open the valve. For instance: The valve is closed after being opened during low tide and water rushes from the stream out to the ocean. The level of the stream and ocean are now low. The valve closes again, and time is allowed to pass. High tide comes and the ocean water level is now two feet above the stream water level. When this difference is detected, the valve automatically opens to release a torrent of water into the stream. (these streams are salt, brakish and fresh water, depending on the water height. salt water rises, brakish in the middle and fresh water sinks to the bottom).
-- twitch, Nov 20 2006


yeah, it does seem like my anno is more clear. call it a second draft.
-- twitch, Nov 21 2006


that idea does make sense too I must say. Constant flow (although restricted much at times) would encourage aeration as long as the flow was allowed to splash, which, mechanically, would pose little challenge.
-- twitch, Nov 22 2006


Why do the unmaintained pipes get blocked? Presumably either from stream gravel, or more likely ocean sand carried in on high tide. How does the valve avoid the blockage?
-- bungston, Nov 23 2006


//it's like a laxative for a constipated stream.//

More like an enema.
-- SledDog, Nov 23 2006


Sand blocks pipes coming in with wave action and high tides. It should be mechanically simple to allow a valve to open with some sand blockage, allowing water to slowly take the sand out to sea or into the stream.

I've never really known what an enema is.. I never cared to look it up. And i'm not going to look it up after this anno although I AM tempted. Lazy.
-- twitch, Nov 23 2006



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