Glen Ellen Creek, viewed from the backyard of a client property.

As winter rains approach, protecting your landscape and property from flooding starts with understanding your environment and implementing thoughtful design. Here, we explore three critical elements: reading the land, the role of wetlands, and the importance of a well-designed drainage system.

One of the hardest classes in Landscape Architecture was grading and drainage. It started with a simple challenge, creating a 2% slope on all paths ways. Easy you might think but depending on the distance it could be a challenge. Then we’d have a flat surface such as a large parking area or patio, now we would have to grade for drains. Suddenly this easy to picture exercise became infinitely complex.

But why should you as a homeowner, here in Sonoma County worry about grading and drainage? Well there’s a few reasons, first ensuring water flows away from your home, retaining walls and pools is crucial to avoid structural damage. This is the perfect time of year to start observing where water pools. Are there any safety issues? Do your downspouts dig trenches next to your foundation? Is there a seasonal creek in your yard? Yes the last one is a common issue many of my client face in the winter.

Reading the Land: Flood Plains and Historical Floods

Okay let’s start with doing our homework. With a topography map and some historical data we can look at your property and see how likely it is to be in the path of a big flood. We call these zones flood plains, they’re normally broken up into 10 year, 25 year, 50 year and 100 year. The more frequent the flooding the less of a surprise, it’s normally the 100 year flood that will take homeowners unaware and do the most damage.

Flood plains are nature’s way of managing excess rainwater, and understanding their role is essential for any property owner or designer. Flood plains are low-lying areas adjacent to rivers and streams that absorb overflow during heavy rains. While these areas offer rich, fertile soil for agriculture, they are also at higher risk for seasonal flooding.

In Sonoma County, historical floods have repeatedly highlighted the importance of recognizing flood-prone zones. The 2019 Russian River flood, for instance, caused widespread damage, with water levels rising over 45 feet. These events underline the need for homeowners to investigate historical flood data and FEMA flood maps to determine their property’s risk.

When designing such areas, consider how water naturally moves across the land. Observe the slopes, soil types, and vegetation, as these elements provide clues about where water will pool or flow. This knowledge allows for proactive design choices, such as siting structures on elevated ground or creating channels to direct water away from key areas.

In one of our Glen Ellen projects that was adjacent to the creek we had a designated area that would flood seasonally. Then we build up berms and denser plantings to slow any extreme floods. The house itself was also built up on a raised foundation with the ground floor being all concrete incase of that once in a 100-year storm.

While we can’t always know what mother nature will throw at us. Taking the time to look at past information and plan accordingly can help homeowners be prepared.

Wetlands and Their Role in Reducing Flooding

Now that we’ve looked at historical areas of flooding let’s talk about the natural ecosystems of riparian areas (riverlands). Before we decided to build in this wonderful area, there was a water system in place that could handle extreme fluctuations in rainfall.

Wetlands, often referred to as nature's sponge, play a vital role in managing excess rainfall. These ecosystems absorb and slow down stormwater, reducing the intensity and speed of runoff. By acting as a buffer, wetlands help prevent downstream flooding and protect properties from water damage.

In Sonoma County, wetlands along the Laguna de Santa Rosa offer a natural solution to heavy rains. They not only mitigate flooding but also filter pollutants, recharge groundwater, and support biodiversity. Protecting or restoring wetlands on or near your property can significantly reduce the need for extensive artificial drainage systems.

For properties not adjacent to wetlands, consider mimicking their functionality by incorporating rain gardens and bioswales into your landscape. These features capture rainwater, allow it to infiltrate slowly into the soil, and support native plants that thrive in wet conditions. These strategies not only manage stormwater but also enhance your landscape’s beauty and ecological value.

I was recently on a hike with the Sonoma Land Trust that covered the work they’ve been doing with wetland reclamation. Sonoma Land Trust's wetland restoration initiatives have significantly contributed to flood mitigation in Sonoma County. A 2012 study on lower Sonoma Creek indicated that while isolated projects might not substantially reduce flooding, a comprehensive, watershed-wide approach could offer notable flood reduction and habitat restoration benefits. The study recommended transitioning flood-prone lands to flood-compatible uses, such as acquiring easements for seasonal flooding and restoring tidal wetlands.

In line with these recommendations, Sonoma Land Trust has undertaken large-scale wetland restoration projects, including the Sears Point Tidal Wetland Restoration. By reintroducing tidal flows to previously diked areas, these efforts have revitalized natural hydrological processes, enabling wetlands to absorb and slow down stormwater. This natural absorption reduces the velocity and volume of runoff, thereby decreasing the risk and severity of downstream flooding.

Moreover, the restoration of tidal wetlands serves as a buffer against sea-level rise and storm surges, providing a resilient defense that protects both ecosystems and human communities from flooding. By integrating wetland restoration into flood management strategies, Sonoma Land Trust effectively leverages nature-based solutions to enhance regional flood resilience.

For more detailed information on these initiatives, please visit Sonoma Land Trust's official website: https://sonomalandtrust.org.

Drainage: How a Good Drain Design Can Keep Your Property Protected

The backbone of flood prevention on a smaller scale starts with your property. Proper drainage designs ensure that water flows away from structures, prevents pooling in unwanted areas, and minimizes soil erosion. When done right you can minimize your part in your community’s storm water issues and increase the health of your own land.

Or course we would suggest hiring a professional landscape contractor to help you with this next step. However I’m a firm believer in knowing how something works so you can ask for what you need. Taking photos of areas where water pools and having observations during heavy rains can help when you’re talking to an installer in the middle of summer.

Key Components of Effective Drainage Systems:

Grading and Sloping: Ensure the land slopes away from your home or structures to prevent water from collecting around foundations.
Gutters and Downspouts: Direct roof runoff to safe areas, such as drainage pipes or rain gardens, to prevent erosion near the house.
French Drains: These systems use perforated pipes surrounded by gravel to divert water underground, particularly useful in areas with heavy clay soil like Sonoma County’s Adobe clay.
Permeable Surfaces: Replace impermeable surfaces like concrete with permeable pavers to allow water to soak into the ground.

The following is how we would go about working out a new drainage plan for your property. Steps 1-2 are a must for homeowners whether you plan to DIY or hire a designer / installer.

Step 1: Assess Your Property

Observe Water Movement: After a rainfall, note where water pools or flows.
Identify Problem Areas: Look for low spots, foundation puddling, and erosion-prone zones. Ideally photography or video the areas during a hard rain.
Analyze Soil Type: Sandy soils drain quickly, while clay soils may retain water and require additional solutions.

Step 2: Create a Drainage Plan

Map Your Property: Draw a rough map showing slopes, structures, and problem areas.
Plan Water Flow: Identify paths to redirect water safely toward storm drains, swales, or natural runoff areas.
Select Features: Decide on drainage components based on your property’s needs, such as French drains for subsurface water or bioswales for surface runoff.

Now we enter the Installation part.

Step 3: Regrade the Land

Ensure Proper Slopes: Grade the ground to create a minimum slope of 1 inch per 10 feet away from the house. Ideally a 2-5% slope where at all possible
Build Berms: Use soil mounds or walls to divert water around structures.

Step 4: Install Gutters and Downspouts

Clean Existing Gutters: Clear debris to ensure proper water flow.
Extend Downspouts: Add extensions or splash blocks to redirect water at least 5 feet from the foundation.

Step 5: Implement Surface Drainage

Create Swales: Shallow channels lined with grass or gravel to guide water.
Install Catch Basins: Place them in low spots to collect water and connect them to underground pipes.

Step 6: Add Subsurface Drainage

Dig Trenches: Excavate trenches for French drains or pipe systems.
Install Drainpipes: Use perforated pipes wrapped in fabric to prevent clogging and backfill with gravel.

Step 7: Utilize Permeable Surfaces

Replace Impervious Areas: Swap concrete or asphalt with permeable pavers or gravel.
Install Dry Wells: Create underground storage for excess water to percolate into the soil.

Step 8: Incorporate Eco-Friendly Features

Plant a Rain Garden: Use native plants to absorb and filter runoff.
Build Bioswales: Line them with deep-rooted plants to slow water flow and improve absorption.

Step 9: Regular Maintenance

Inspect Drainage Features: Check for clogs, sediment buildup, or damage.
Clear Debris: Remove leaves, branches, and other obstructions from gutters, drains, and catch basins.
Regrade Annually: Address soil settling or erosion that may alter slopes.

Design is critical here. Hydrological analysis, soil testing, and topographical surveys can inform the placement and sizing of drainage features. Integrating these elements with landscaping not only prevents flooding but also improves the aesthetics and functionality of your outdoor space.

Conclusion

Preparing for the rains requires a deep understanding of your land’s history, the power of natural ecosystems like wetlands, and the impact of thoughtful drainage design. By combining these elements, you can protect your property from flooding while enhancing its natural beauty and sustainability. Whether you’re considering a new project or upgrading your existing landscape, a proactive approach will pay off when the rain arrives.

Ready to safeguard your property and elevate your landscape? Contact us for a design consultation today!

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Sources

100 Year Flood Plain Map
https://permitsonoma.org/x105605
FEMA. “Flood Maps.” FEMA. https://www.fema.gov/flood-maps

EPA. “Green Infrastructure: Mitigate Flooding.” Environmental Protection Agency. https://www.epa.gov/green-infrastructure

Wikipedia Contributors. “2022–2023 California Floods.” Wikipedia. https://en.wikipedia.org/wiki/2022%E2%80%932023_California_floods

American Red Cross. “Flood Safety.” American Red Cross. https://www.redcross.org/get-help/how-to-prepare-for-emergencies/types-of-emergencies/flood.html

Ready.gov. “Floods: Preparedness and Response.” https://www.ready.gov/floods

Express Water Solutions. “Factors to Consider When Designing a Drainage System.” https://www.expresswatersolutions.com/drainage-systems/factors-to-consider-when-designing-a-drainage-system

ArchDaily. “How Cities Are Using Architecture to Combat Flooding.” https://www.archdaily.com/931720

Times UK. “How to Make Our Cities More Spongy and Less Flood-Prone.” The Times. https://www.thetimes.co.uk/article/how-to-make-our-cities-more-spongy-and-less-flood-prone-kqb69nmzb

Better Homes & Gardens. “How to Prep Your Home Before Heavy Rain.” Better Homes & Gardens. https://www.bhg.com/how-to-prep-your-home-before-heavy-rain-8695802

UNEP. “How Climate Change Is Making Record-Breaking Floods the New Normal.” United Nations Environment Programme. https://www.unep.org/news-and-stories/story/how-climate-change-making-record-breaking-floods-new-normal

Building America Solution Center. “Swales, Drains, and Site Grading for Stormwater Control.” https://basc.pnnl.gov/resource-guides/swales-drains-and-site-grading-stormwater-control

The Spruce. “15 DIY Yard Drainage Methods.” https://www.thespruce.com/diy-yard-drainage-methods-5080419

Express Water Solutions. “Factors to Consider When Designing a Drainage System.” https://www.expresswatersolutions.com/drainage-systems/factors-to-consider-when-designing-a-drainage-system

Drainage Connect. “10 Ways to Improve Your Property's Drainage Systems.” https://www.drainageconnect.com/en/blog/post/10-ways-to-improve-your-property-s-drainage-systems

Family Handyman. “How to Achieve Better Yard Drainage.” https://www.familyhandyman.com/project/how-to-achieve-better-yard-drainage

Preparing for Rain: Floods, Wetlands, and Drainage Design