Energy and landscapes
Water
Water is a powerful dynamic substance able to absorb, transfer, transform, and release vast amounts of energy. In consortium with biodiversity and in particular, complex plant systems, water dissipates and distributes the energy from the sun and gravitational forces.
In a healthy landscape, water infiltrates the soil and is retained. Water buffers temperature extremes and supports the plant growth essential for production, biodiversity, and biological activity soils. In a degraded landscape, water runs off and is rapidly lost from the system, taking valuable topsoil on its way.
If we wish to repair landscapes for environmental and farming enterprise outcomes, we need a good understanding of the forces that govern the movement, storage and cycling of water from small to global scales. Sunlight and gravity power the system, driving carbon, nutrient and water cycling through their interaction with plants.
Photosynthesis
Photosynthesis is how plants convert solar energy into chemical energy, the products of which feed all the other kingdoms of life on planet Earth. Plants are the primary producers in the food chain. The rest of us are consumers. Photosynthesis uses sunshine and water to convert CO2 into glucose (C6 H12O6), a carbohydrate which then provides the plant with the fuel it needs to build the complex organic molecules needed for it to grow and produce biomass. These carbohydrates (or sugars) feed and nourish the rest of the food chain, including the microbiome in the soil, livestock, wildlife and people.
Photosynthesis is an energy intensive process, which generates heat. A primary function of evapotranspiration is to keep this process cool, so that it operates as efficiently as possible. For every water molecule used in photosynthesis, roughly 100 molecules are used to keep the process cool. As such, without water readily available for the plant to use, photosynthesis would not be possible.
Gravity
Every landscape has slopes and undulations, and this means gravity is always at play. The form and condition of our landscapes is very much determined by how gravity, compelling water downhill, interacts with rock, soil, and plants.
In any landscape, surface water driven by gravity will concentrate towards a flow path and eventually drain to the lowest point in the landscape. The precise drainage location is known as the re-entry point.
Gravity plays a huge role in the erosion of landscapes by water. This erosion is influenced by four major factors:
Speed
The speed of water has an exponential effect on its erosive power. Water that is three times as fast has nine times the energy. The speed of flow is highly influenced by the three factors below.
Plant cover and surface roughness
Surface cover affects the energy of flow through what’s referred to as ‘roughness’. Examples of roughness include trees, shrubs, tussocks, reeds and submerged plants, sticks, logs, and rocks. Anything that water rubs up against or bumps into will slow it down.
The more ‘roughness’ in the system, the slower the flow. Friction is a major factor, but it is also partly due to the water-on-water principle: water is de-energised when it bumps into itself. Turbulence is created when water bumps into a surface or into itself, which dissipates energy.
When we remove roughness, for example through loss of native vegetation, pasture cover or woody debris in streams, water speeds up. In keeping with the ratio mentioned above, if roughness in a landscape is reduced by 1/3, water will flow over those surfaces three times as fast.
By contrast, natural infrastructure and nature-based solutions aim to improve surface roughness and slow the movement of water in the landscape. Greater surface roughness, primarily through the presence of plants, slows the flow of water and protects soil structure and plant health.
Amount
More water means more energy for a system to manage. The amount of water travelling through the system is influenced by factors such as catchment size and composition. The surface area available for water to flow over can significantly affect water’s energy at a given location. Confined areas lead to concentrated, high-energy flows with erosive potential. When spread over a larger surface area, water slows down, and energy is dissipated.
Slope
The gradient of a slope can be characterised as gentle, moderate, or steep. The steeper the slope, the faster water flows, influencing the energy of water moving through the system. Where the gradient of a slope decreases, the energy of water also reduces, slowing the flow. Surface roughness, amount of water flowing over a given point, and slope all interact to determine the erosive power of water.