Some people walk in the rain, others just get wet.
~ Roger Miller
“If you want to understand hydrology, go stand in the woods in the rain,” he instructed. We looked at our environmental engineering professor as if he was crazy, but over the next few weeks, most of us tried it.
Once I was used to being a little wet and got over feeling stupid, I started to notice things. Water pooled on my raincoat and hat, and ran in rivulets to spill onto the ground. The rain fell in splatters on the dirt and splashed off the leaves. Some soaked into the ground, but much of it either pooled in depressions, like those caused by my boots, or flowed over the surface to merge into small rills flowing downhill. I followed one set of rills and watched them combine with others to form bigger and bigger flows that moved the dirt and pine needles downstream. The soil squished under my feet, becoming mud as it absorbed the water.
The flows collected in a small stream that formed a channel roiled with water, soil and debris. Where it flattened, the soil and debris would settle out, only to be moved further if higher water intruded. The multiple streams combined into bigger and bigger streams moving down to the river.
I watched the river roll past and noticed the sticks and leaves, and occasional piece of trash, carried in the flow. Where the stream higher up was mostly clear, the river here was brown with mud. After the rain, the water receded, leaving a film of silt and debris in its wake.
In developed areas, we try to contain the water to keep it civilized and out of our way. We build curbs, storm drains, ditches and channels to move the water away from us. The storm water carries downstream all our urban and suburban debris, along with spilled fuel and chemicals, and applied herbicides, fertilizers and road salt.
Recently, in Florida, Houston and other places, we have been shown how rain and storm water don’t always comply with our desire to control them. They have their own ways, and our attempts can be futile. However, some engineers and planners are exploring the idea of using nature’s own systems to manage water, as opposed to our regimented controls.
Diana Budds reports, “Keeping rainwater close to the site where it lands helps alleviate these pressures on storm water infrastructure, which ultimately makes it more resilient.” Several cities have adopted a strategy they’ve nicknamed, ‘Making Room for the River,’ “which means giving the rivers and waterways room to breathe. This required giving more space to the rivers so they could meander and swell naturally and take on extra water during storms. But these areas were also turned into parks and public amenities for all the other days when flooding isn’t an issue.”
The key in urban areas is to improve permeability, so that more water seeps into the ground, replenishing the groundwater. This mimics the natural systems, as reported by Diana Budds, “A few of the tools in the green infrastructure kit? Infiltration ponds, rain gardens, bioswales, permeable pavement, open space, and green roofs. The more of these natural systems cities adopt, the less they have to rely on heavy engineering, which can fail, requires maintenance and constant upkeep, and is expensive to operate. What’s more, traditional infrastructure was built to specifications that are now in flux, as climate change makes rainfall and storms less predictable.” Others are considering floodable forests, wetland gardens and transforming some traffic lanes into bioswales, which are landscaping elements designed to collect storm water then let it slowly percolate back into the earth.
Another issue with our water management practices is control of sediment associated with streams and rivers. Dams collect sediment historically provided by rivers and deprive downstream areas of the materials that build up the marshes and wetlands that act as a buffer against rising seas. “It’s almost like it’s the food — the nutrients, minerals, and vitamins — these systems need to grow and adapt, and we are starving them of that,” says Robin Grossinger, a senior scientist with the San Francisco Estuary Institute. As reported by Jim Robbins, “Wetlands — including marshes, sea grass beds, estuaries, and mangroves — are remarkably rich and productive ecosystems, providing nesting habitat and nurseries for fish, birds, and other wildlife.”
Sediment removal has another impact, too. Coastlines are defined by the sediment discharged by rivers. The shallow water and resulting marshes or other habitat protect the coast line from storm waters and disperse the energy of incoming waves.
Ellen Wulfhorst reports, “Many low-lying coastal regions in the United States face erosion and rising sea levels, linked to climate change, but the Mississippi delta is particularly vulnerable because it is sinking as well.” She continues, “Deprived of silt and fresh water, and sliced by hundreds of miles of deeply dredged shipping channels, the shrinking wetlands are growing less effective as natural barriers to storm surges from hurricanes, putting the area at higher risk of devastation.”
Brett Milligan, an assistant professor of landscape architecture at the University of California – Davis, feels that rather than consider sediment a waste product, people should consider a “sediment-shed” — akin to a watershed — “and how this precious resource can be utilized.”
In many states and countries, old dams are being removed to restore salmon runs, and this also releases the pent-up sediments. Some dams have been designed to pass sediments through their structures, as well. Jim Robbins notes, “Dam removal has taken back the trapped sediment and distributed it downstream, causing the riverine ecosystem to be rebuilt and transformed. Massive quantities of silt, sand, and gravel have been carried to the coast, resurrecting a wetlands ecosystem long deprived of sediment.”
Robbins also notes that “There are, however, ways to restore the flow of sediments that do not involve dam removal. Sometimes sediment is simply dug up and moved or channeled around the dam in pipes or sluices. Bank stabilization structures can be removed in the river sections where sediment is needed so that more sediment can enter the river and flow downstream.”
As an engineer, much of my training was about how to control nature. However, when I stood in the rain, got wet and got a little smarter, I understood a little more about how all things in nature are connected. The real challenge is to connect with nature rather than fight it. Take a walk in the rain and see for yourself.
If there is magic on this planet, it is contained in water.
~ Loren Eisley
Diana Budds, The Cities of the 21st Century Will be Defined by Water, September 5, 2017, Co. Design Daily Newsletter
Jim Robbins, Why the World’s Rivers Are Losing Sediment and Why It Matters, June 20, 2017 YaleEnvironment360
Ellen Wulfhorst, Fight, flee, or wait and see? Locals face hard choices as Louisiana coast recedes, Jul 5, 2017, Reuters Intel,Thomson Reuters Foundation