The water cycle on Maui involves all parts of the geography from Mauka to Makai.
Water Transit pathways Mauka to Makai start at the highest peaks with the “water harvesters”. The slopes are the watersheds, are “rain catchers”, and the soils are “water absorbers”, and the forests are “water regulators”, Water vapor is transported to the islands over thousands of miles of warm oceans. Evaporation from the ocean’s surface accumulates and rises up into a column of water vapor. These vapor columns are moved along with the weather and winds. This river of water vapor is sometimes called an “atmospheric river”, or “sky-river”. This continuous process is like a virtual conveyer belt bringing precious H2O to us.
Our Mountains Harvest the Water: Our tallest volcanic peaks are perfectly situated to stand in the path of the balmy trade winds and reach into the saturated sky river. Water vapor saturated air, is forced up the slopes of Haleakalā and Hale Mahina, and becomes cooled due to the effects of “adiabatic cooling”. Water vapor condenses directly on the vegetation of the high forests and on the rocks.
About the Mauna (mountains): Hale Mahina is more commonly known as the West Maui Mountains. The name “Hale Mahina” means House of the Moon, named after Hina, a lunar goddess. And “Haleakalā” means House of the sun. Another name for Hale Mahina is “Kahālāwai”, which means House of Water. Mauna Kahālāwai is home to unique native species and ecosystems that exist nowhere else in the world Source: https://www.maunakahalawai.org/mauna-kahalawai-west-maui-mountains
Water droplets form and begin to trickle downward, some of these fall into the cracks and continues their journey downward through underground soils and rock layers. Many lava tubes and rock layers were formed on the volcano’s slopes, and these serve as conduits for the waters to flow. These streamlets join together and become larger streams that find ancient pathways through soil and stone and moves downhill towards the sea. Some of this water accumulates in dikes, which are rocky reservoirs, and some make it down to the aquifer near sea level.
Clouds form on the slopes and create rain. Rainclouds are a common sight on our mountain slopes because of the orographic effect. Orographic rain occurs when the moist air flowing up and over the mountain slopes is cooled so that clouds form and eventually rain falls. At higher elevations in Hawaii, we get a temperature inversion, known as the trade wind inversion layer. This is caused by air descending and warming from higher up in the atmosphere. The trade wind inversion layer occurs at approximately 6,000 feet (1,800 m) above sea level. Above this layer, trade-wind-produced clouds cannot rise. This inversion layer tends to cap our mountain clouds. This is why the clouds often wrap around the peak of our mountains like a kind of of Lei. And this is why we often can have a great view from the top of Haleakalā while there is a thick layer of clouds below. Most of the rain on the 10,028 foot high Haleakalā falls around the middle elevations. On Hale Mahina, clouds often reach all the way up the highest peaks (“Pu’u Kukui” elevation 5,787′) and create the most rain near the summits.
Wettest places on Earth: Hawaii’s most famous “wettest spot” is Mount Wai’ale’ale on Kauai. Which is commonly thought of as one of the wettest places on earth. Maui’s best-known wettest spot is Pu’u Kukui. But Maui has one even wetter place than that right on Haleakalā, it is a little-known perched wetland known as “Big Bog” with and average 30-year rainfall of 404 inches or 10,300 mm per year. Unfortunately, there has been a marked decrease in precipitation at the location since 1990.
When the rains fall on the slopes it saturates into the top soil where it feeds plants and when there is too much to be absorbed, the rain flows over the ground into gullies, and gulches. Ancient Ephemeral Streambeds spring to life and the water flows seaward. Sometimes streams will disappear into lava tubes and reappear again down slope. Sometimes they are waylaid by perched wetlands, pools, and bogs. Strong rains can quickly build into torrents that flow quickly down the mountain. Steep gulches and ravines and the occasional waterfalls along their way.
Huge watersheds feed into narrow gulches, and the streams swell with the water from billions of rain droplets moving together. Watersheds of thousands of acres often feed into narrow gulches a few dozen feet wide. Once on the move the torrent can become a flood, and gains energy as it flows faster down the steep gradient. The water now scours the hillsides and brings along soil and stones, carving the gulches deeper and rolling the pohaku over millions of times grinding the stone smooth and tearing away the soils. Water once energized is a force of nature, that is irresistible, and has the power to transform and carve the landscape.
Water alters the landscape:
Water tears at the sides of the mountain and changes the landscape in spectacular ways. Masses of debris from the mountain slopes is brought to the seashore, and dumped at the foot of the mountain at the shoreline. Thousands of years of depositions form the coastal flood plains and fill the valleys that join our island together in the central valley.
The Kīhei Floodplain:
The Kīhei Floodplain is the product of water flowing and transporting and depositing rock and debris at the foot of the volcano. This creates a floodplain that has a flatter slope. And this becomes an area that slows the fast-flowing flood waters which allows them to shed their load of mud and rock. With each flood more material is delivered to the floodplain, where is continues to build new land into the ocean and become new shoreline. This shoreline building process is known as coastal accretion.
In Hawaii we also have active lava flows directly building new land, and we have the water style eroding the rock and making sands and soil that build up the shoreline areas and coastlines. At the beaches we also have the coral sands that are created by the sea life that also accumulates at the shoreline giving us our white sandy beaches.
This is where coastal wetlands come into play.
Coastal wetlands are the guardians of the sea, and the land. They stand between these environments and the feed off the waterflows coming from both land and sea.
The water from Haleakalā for example flows underground continuously, and the streams flow aboveground occasionally with the storms and flash floods, these often come together on the slopes of the flood plains where the waters have a chance to expand and slow.
The aquifer is an underground layer of water-bearing permeable rock and sediments. In Hawaii our aquifer contains a vast body of groundwater. Groundwater is the result of rain water that has soaked into the ground and filtered down through rocks, sediments, and and crevices down into the aquifer. The aquifer tends to filter the water as it moves through the aquifer as it passes through small gaps and the pores of the rocks. Most debris and particles can be filtered out of groundwater in this way, but other dissolved contaminants remain in the water and are not filtered out., Groundwater is tested for contaminants before it can safely be used for drinking water In the aquifer close to sea level, a layer of fresh groundwater sits on top of a layer of salt water from the ocean. Salt water is denser than fresh water so they are separated by buoyancy. The freshwater sits on top of the salt water, but where the two layers met they mix in a brackish layer.
There are many wells drilled into our aquifer,
and humans extract vast quantities of this natural resource for various purposes including for drinking water and for watering golf courses. Depending on the location of the wells, the quality of the water varies. Many wells have become contaminated from years of toxic chemicals being used for agriculture. Contaminated wells are still often used, but the water usually needs to be filtered before use. Some wells are pumping brackish water that may be unsuitable for drinking, but may still usable for irrigation or industrial uses etc.
The aquifer takes many years to recharge from rainfall, maybe thousands of years in some cases. And we are generally extracting water faster than it can be recharged. The water moves through the aquifer powered by gravity, but it does not flow quickly like a river because it is moving through rock or sediments. And the rate at which the water moves through the aquifer varies depending on the porosity of the material. The result of over extraction of freshwater from the aquifer is that the salt water layer rises. This is called a “rising saltwater table”. And this can bring up the salt water into soils and it can destroy agricultural land as well. The “freshwater lens” of the aquifer, pushes down on the salt water layer, and keeps the salt water table lower, but when the freshwater is reduced there is less hydrostatic pressure holding down the salt layer.
Many coastal wetlands lie n the gulches and streambeds near the ocean. The debris and sediment from the stream and the sea form a barrier wall “puʻuone” like a sand bar or rock dam. This creates natural pools that we call a Muliwai. There are many permanent (perennial) pools that are easily recognizable as wetlands, these become habitats for specialized animal and plant life. There are also Wetlands that are ephemeral and may only appear seasonally, or during and after rains. There are also wetlands that have no visible surface water because the water remains just below the surface. Wet soils of wetlands sustain a multitude of organisms, many of which are unique to that environment. The perennial wetlands are a repository of biodiversity and are a haven for endemic species. Even our ephemeral wetlands are a vital link in the life cycles of many wetland-dependent organisms. And form a key component of these ecosystems.
Many species spend a part of their life-cycle in the wetlands, estuaries, and stream mouths. For example, various oceanic species come to these places to breed or lay eggs, and wait for the occasional breech in the barrier walls from floods, or wait for high tides or waves to overtop the barrier dunes for example.
Water enters the ocean: The journey of rainwater doesn’t stop at the shoreline, it continues to flow into the ocean. Most of us already know that freshwater water flows from the surface in streams and waterfalls and into the ocean, it also percolates through sand dunes and enters the ocean at sea level. But freshwater can also be produced from underwater springs.
Maui is surrounded by thousands of freshwater springs that are in the ocean, some are just offshore, and can be seen bubbling and swirling the water, and some of the springs will be located far offshore and come up quite far away from the shoreline. These springs ware known to the ancient Hawaiians as a viable source of drinking water and the best freshwater springs in the ocean were used as places to collect freshwater.
About Atmospheric Rivers
Hawaiian names for wind, clouds and rain
About The Mauna