Earth Matters: Native plants can combat flooding on L.I.

Earth Matters: Native plants can combat flooding on L.I.

By Lynn Capuano

It’s been nearly two weeks of practically constant rain and snow across California, causing flooding, levee breaks and evacuations. At least 17 people have died and the property destruction is incomprehensible. The rainfall has exceeded average rainfall for nearly all parts of the state by 400 to 600 percent. With more rain in the forecast, flooding and more property damage are assured because the ground cannot absorb any more water.

Like a sponge, the available undeveloped land is saturated. Further rainfall will not be soaked up by the soil, but will pool and follow the path of least resistance, unleashing flooding and other harm as it flows. Creeks and rivers are overwhelmed and cannot contain all the water that is falling.

While scientists and others discuss how this is another example of the climate change impact of fossil fuels, we should be thinking about how we can prepare for a similar event here on Long Island. Superstorm Sandy is recent history, and we should all understand that weather patterns of the past are just that, the past. What we will experience going forward is much more unpredictable. We do know storms will be more severe and the risk of flooding and drought are much higher. Interestingly, a response to both is the same: improve the land’s capacity to absorb water.

In a flood, the land’s ability to absorb water is critical to minimizing flooding. If the water is soaked up by the land, then it cannot pool in places and cause flooding. In a time of drought, reservoirs of water in the ground are critical for providing needed water both to people and plants. The capacity to absorb water is affected by the quality and nature of the land.

Developed land, or land where soil is no longer exposed and plants do not grow, does not absorb water at all. The only exception to this is streets, parking lots or other paved surfaces that are paved with permeable material that allows the water to seep in and be absorbed by the soil underneath.

While undeveloped land will absorb more water than developed land, where the water runs off the surface, not all undeveloped land is equal.

A standard lawn will not absorb as much rain as a yard full of native plants. A yard of grass will flood in heavy rainfall because the grass, and its root system, cannot take in as much water as other plants like trees and native plants. Instead of drawing in water through its root system and helping it disburse into the soil, a lawn will let water pool on the surface and cause flooding. In some cases, depending on the health of the soil in which the grass is planted, the root system may be so weak that the entire top layer washes away in heavy rain.

This has to do with the health of the soil and whether the plants are helping to hold the soil in place. The soil under chemically treated lawns is not as healthy as soil left alone and fed with fallen leaves and populated by various insects and invertebrates. It is more susceptible to having its top layer eroded by rain. Soil that is full of native plants and trees and fed by organic matter will stay in place and will fill itself with water, allowing more and more to flow deeper underground.

Yards planted with native plants can absorb many times as much water as a lawn, thereby reducing the risk of flooding and also storing more water for use during a drought. Native plants can do this because of deeper root systems that can draw water deep into the ground. They are also better able to store water and use the water made available. One study demonstrated that the soil under a mix of native trees absorbed water 67 times faster than soil under grass. The root systems create pathways for the water and the soil can hold the water, making it available to the plants when needed.

We are not immune from the risks of flooding as our neighbors in Queens and on Long Island can attest to. In this highly developed area there are not a lot of open spaces where the rain can be absorbed. With the runoff from all the paved areas needing to find somewhere to go, the sewers and the open land can be overwhelmed.

We can help by installing plants that can handle both heavy rain and drought. Plants that are native to this area are best suited to thrive in our changing climate. They are most adept at mitigating any extreme weather we experience. There is plenty of information online and through talks and webinars sponsored by the Town, library and many community organizations. Local nurseries can also help. As an added bonus, these plants often will also attract pollinators and birds, bringing an extra layer of beauty and health to your yard.

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