Flooding in the Pacific Northwest seems to have gotten worse over the last couple of decades, which unfortunately makes sense given the increase in climate change impacts, the increase in urban development, and the region’s numerous and intricate waterways. Different parts of the Pacific Northwest have seen increases in river flooding and coastal flooding, with Seattle seeing three times as many coastal flood days in recent years compared to the 1950s. Whatcom County in Washington also experienced catastrophic flooding in November 2021 that resulted in millions of dollars in damage. In December 2023, at least two people died in Oregon after yet another atmospheric river hit Oregon and Washington and resulted in more flooding. There are a few reasons why flooding has increased but there are ways we can reduce the potential injuries or death, property damage, and environmental harm.
Types of Flooding and Their Causes
There are a few different types of flooding that occur and different reasons as to why they might happen. Fluvial flooding is the most common type and is a flood that occurs in and around lakes, streams, or rivers. It could either be overbank flooding, when the water rises over the edges of a river, stream, or lake, or flash flooding, when a high volume of water moves at a high speed with little warning through an existing riverbed. Pluvial flooding is when increased rainfall creates a flood independent of a nearby body of water and can happen anywhere. Coastal flooding is the influx of seawater into coastal land, often caused by high tides, storm surges, and tsunamis, and can clog stormwater drains, flood streets, and affect freshwater supplies. King Tides are particularly dangerous, as these tides are the highest astronomical tides of the year and can worsen or compound flood risks.
All three types of flooding are influenced by climate change, with increased rainfall, rising ocean levels, and an increase in more devastating natural disasters like hurricanes have resulted in more flooding events. Flooding isn’t always directly because of climate change though, as it’s a complex process with many different interrelated factors. These factors include impermeable surfaces, development and urbanization of the area, tree cover, the presence of native vegetation, soil types, the topography and geology of river beds, and clearcut forests. Heavier precipitation as a result of climate change has also resulted in more floods, as evidenced by the recent upticks in atmospheric rivers in regions like the Pacific Northwest. Higher sea levels are, understandably, resulting in more coastal flooding events.
Impervious Surfaces as a Direct Result of Urban Development
Urbanization and development play a huge role in flooding, as anthropological impervious surfaces have a huge effect on the local watersheds and groundwater. King County Code (the county where Seattle, WA is) defines an impervious surface as “a hard surface area which either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development, and/or a hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development.”
Basically, impervious surfaces like paved roads and parking lots result in water not having space to go and prevent rainwater from being absorbed into the water table to slowly seep into streams and rivers or replenish groundwater aquifers. This, in turn, causes groundwater tables to be used far more quickly than they can be recharged and for more puddles or larger bodies of standing water. Development and impervious surfaces can also alter the capacity of nearby streams and rivers, increasing flooding, erosion, and sediment/debris obstruction.
Stormwater Pollution
Flooding isn’t the only issue at play when discussing impervious surfaces and increased urbanization. Stormwater from impervious surfaces like roads also increases runoff/nonpoint pollution, which has incredibly far-reaching effects. One chemical in particular from toxic runoff has been killing coho salmon in the Puget Sound for decades and scientists were only recently able to identify it as 6PPD-quinone, a chemical found in car tires. This chemical isn’t the only thing found in stormwater runoff either, as literally anything dumped or dropped on the ground or in a gutter could end up there as well. Pesticides, like garden fertilizers, cigarette butts, used motor oil, pet waste, and more have all ended up in stormwater systems and can cause all sorts of damage.
Water from the Woods
The above video highlights the importance of forests in water management and how healthy forest ecosystems can help regulate seasonal river flows. Ecological forestry and sustainable practices can help with the increase in winter flooding and the increase in summer droughts we’ve been seeing over the last few years. Clear-cutting forests for development, logging, or any other reason can have numerous effects on the environment, including how often or how big a flood could be.
It’s not difficult to make the connections between the effects of increased urbanization, the related rise in flooding and pollution, and the effects that wildlife are feeling. As we (the royal we as humans) continue to increase the number of impervious surfaces, clear more forests, and all around affect the water cycle at large, we have a much larger impact on our local ecosystems and planet. In a time where we are already experiencing water crises, exponential extinction rates, and increased natural disasters, we cannot afford to indiscriminately develop more land. Intentional and sustainable development, fixing existing issues in developments and impervious surfaces, developing solutions and sustainable alternatives, and providing safe and affordable housing are ways in which we can safely move forward in caring for the planet and people.
