As summer approaches in Santa Cruz, we’re excited to embrace the sun, fun, and nearly limitless outdoor recreation opportunities that our fair weather supports. It can be easy to forget that just four short months ago, our community was being drenched in heavy rains, our riverbanks were filling, and the sun was nowhere to be seen. 

Heavy winter rains brought by chains of atmospheric rivers can fill the San Lorenzo River and, in the most serious cases, overtop the river’s banks, cause landslides, flood homes and businesses, close roads, and cut electricity for neighborhoods throughout the region. While a river rising past flood stage can bring plenty of stress and damage during a winter storm, these events can also have plenty of positive effects on our watershed. Flooding plays an important role in the aquatic ecosystem and our watershed’s health.

Let’s explore how the San Lorenzo River’s streamside plants, animals, and water quality benefit from occasional flood events. 

Plants: Our native plants have existed alongside floods for millennia Seeds of some native riparian species(sycamore, for example), sprout most successfully when saturated and covered by water, which only happens during the wettest winters. Round seeds of the California buckeye tree have evolved to roll or wash downhill into creeks and to float, supporting seed dispersal and germination. High river flows flush fine sediments and minerals downstream, and as the river recedes those rich minerals are left behind, enriching the soil for native plants. Many native riparian species have underground root tubers that allow them to thrive in wetter-than-average conditions, outcompeting introduced plant species and using their root systems to hold soil in place, reducing erosion.  

Animals: No need to fear that all the tadpoles and other small critters get washed into the ocean during flood events! Most aquatic animals lay their eggs after the storm season passes, so their juvenile life stages have the spring, summer, and fall to develop into adults that can find shelter out of the river channel during high winter flows. Steelhead trout and salmon benefit from especially high water levels so they can swim further up small creeks to find suitable habitat for laying eggs. Wetland and marsh areas stay wetter for a longer time period after flooding, supporting amphibians like frogs, newts, and salamanders, as well as their food web. 

Water Quality: Like a sponge, healthy soils soak up a LOT of water and release it slowly. Large rain events recharge our groundwater, which is needed to provide local drinking water and to create the springs that form our creeks. When groundwater levels are high, we also see higher summer base flows in the San Lorenzo River – which means more water for people and nature to enjoy when it is hot and dry! The force of high river flow events also flushes away pollution and excess sediment, which improves the habitat and makes our river healthier and cleaner. 

Impacts from floods and huge rainstorms are not to be taken lightly, especially through the lens of our human community’s safety and infrastructure. Preparing for flooding before big storms hit, such as by packing an emergency kit, creating an emergency plan, and knowing where to get information about emergency conditions, can help us live in harmony with a dynamic neighbor like the San Lorenzo River. From an ecological perspective, floods are a natural process that can positively affect watershed health and provide a source of life for plants, animals, and people.  

High flows on the San Lorenzo River in Santa Cruz, CA – January 2023

You can help support a healthy watershed! Maintain your personal vehicles to prevent chemicals from leaking onto our roadways, check your sewer lateral pipe or septic system to prevent sewage seep, reduce your water usage, and plant local species to support our soils and our local wildlife. You can also donate to organizations like the Coastal Watershed Council who are dedicated to protecting local rivers and streams for people and planet. We all have a role to play in keeping our river and watershed thriving year round. 

To learn more about the benefits of flooding, watch this presentation that CWC gave at the 2024 State of the San Lorenzo River Symposium!  

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