Exploring the Big Island of Hawaii
The Hamakua coast on the north east shore of Hawaii Island features steep volcanic cliffs divided by deep fertile valleys. Prominent among them is the Waipio Valley, almost a mile wide and six miles long. The valley once the home of Hawaiian kings has historical and cultural significance. On a Thanksgiving Day 2012 hike I descended one of the steepest public roads in the United States (25% grade) to explore the unique ecosystem along the valley floor.
The mouth of the Waipio opens to the Pacific Ocean, the towering enclosing cliffs are nearly 2,000 feet high, there are a hundred waterfalls and the valley creates it’s own hydrologic cycle. The physical movement of water through the environment can be observed in the atmosphere, the land and sea at Waipio.
Evaporation. When water changes from a liquid to a gas the primary force behind it is solar radiation. The water cycle involves the exchange of heat, which results in evaporative cooling of forests and oceans. 86% of the global evaporation occurs from the oceans.
Water Vapor. Water in its gaseous state is invisible but in heavy concentrations it can be visualized as a mist. A warming planet could allow water molecules to attain a greater height in a more humid upper atmosphere and even into the exosphere where the accelerated loss of hydrogen to space is possible.
Condensation. The transformation of water vapor to liquid water droplets in the air, creating suspended clouds and fog.
Transpiration. Plants absorb moisture through their root system which then travels capillaries within the stem or stalk to be expelled by leaf cells as water vapor. Only a small portion of the water that plants absorb are retained in the plants.
Precipitation. Water may fall to the Earth as rain, snow, hail, sleet or fog dripping
Interception. Not all precipitation that falls from the sky reaches the ground. Every object that ‘gets wet”, the trees, leaves, organic mass and man made structures intercept the rainfall, releasing it back to the atmosphere by evaporation.
Infiltration. Infiltration is the flow of water from the surface into the ground. Once infiltrated, the water becomes soil moisture or ground water.
Percolation. The movement of water through the soil, geologic formations in the Earth’s crust and conduits to subterrainiun reservoirs. Water is always moving, although sometimes very slowly.
Gravity. The prime moving force of ground water is gravity.
Cleansing. The water cycle purifies the water and air, replenishes the land with fresh water and transports minerals around the planet.
Runoff. The total flow from a drainage basin or watershed that accumulates in channels, surface streams and rivers is measured as the base flow.
Runoff. The flow of water over land and beneath the Earth is the method that sediment and biogeochemicals are transported from one location to another. Nitrates from fertilizer washed out of agricultural fields are causing eutrofication of lakes and waterways around the planet. Sediments that are carried in free flowing rivers are impeded by dams which cause silting in reservoirs.
Storage. A fundamental characteristic of the planetary water cycle is that it has no beginning and it has no end. Water is stored in the atmosphere, on the surface of the Earth and underground while continuously moving through these mediums and cycling through various processes. On average, water in the atmosphere is renewed every 16 days. Soil moisture is replaced about every year. The residence time in rivers is 2 to 6 months while in lakes it is about 17 years. Oceans can store water for over 3,000 years.
Human Activities that alter the water cycle include:
- alteration of the chemical composition of the atmosphere
- construction of dams
- deforestation and afforestation
- removal of ground water from wells
- water abstraction from rivers
The Waipio Valley is an unspoiled slice of old Hawaii. Development has not intruded on this pristine native habitat nor is it likely it ever will. Other ecosystems around the planet are not so fortunate. Learn what challenges face your water future.