Lyon Creek: How Erosion is Impacting Three Adjacent Properties
A Visual Timeline of Creek Changes and Their Effects on Mark Garey’s Property, Jang’s Property, and the Downstream Neighbor
Why This Matters: The Environmental and Structural Risks at Lyon Creek
Between November 16, 2021, and January 7, 2022, under two months, Lyon Creek has undergone significant erosion and destabilization, threatening the properties of Mark Garey, Jang (my property), and the downstream neighbor. The creek’s rapid changes are not just a natural phenomenon—they are worsened by flooding from an upstream detention pond and failing drainage systems.
Key Concerns:
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Erosion and Land Stability – The creek is actively cutting into the bank on Mark Garey’s property. The loss of a large tree, whose roots once stabilized the soil, has accelerated erosion. Without intervention, the bank will continue to erode, potentially leading to slope failure, affecting both his property and those downstream.
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Changing Water Flow and Flood Risks – As the creek shifts its course, it alters water velocity and direction, increasing flood risks for all three neighboring properties. Water moves more aggressively, affecting the Garey property, my home, and the downstream neighbor.
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Impacts on Neighboring Properties – Changes in creek flow don’t stop at one property. As erosion continues at the Garey site, more sediment and debris are carried downstream, potentially clogging culverts see the pictures and videos and increasing flood hazards for everyone along the creek. All 3 of our properties and in danger of a landslide as our two houses are on top of steep slopes.
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Infrastructure Vulnerability – The upstream and downstream culverts are critical for controlling creek flow. If erosion continues unchecked, these culverts may become blocked or structurally compromised, worsening flooding and environmental damage for all three properties.
This page provides a visual timeline to illustrate the increasing risks to the community and why immediate action is necessary.
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Before the Changes: Lyon Creek in Springtime 2020
Before the erosion intensified, Lyon Creek was a stable, slow-moving stream with dense vegetation helping to anchor the soil and prevent major changes in the creek’s path. Lyon Creek in springtime, when vegetation stabilized the banks, reducing erosion. The contrast with later photos highlights the damage that followed. Notice that the large tree in the middle is still standing. In the spring and the summer, it is hard to hear the trickle of the shallow stream and to see it.
Upstream Contributors: The Detention Pond & Flooding Drain
While seasonal rains contribute to creek fluctuations, flooding from upstream infrastructure failures is making the situation worse.
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The Detention Pond (Upstream) is Overflowing
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Designed to control stormwater flow, this pond has been overwhelmed by heavy rain, sending high-velocity water into Lyon Creek.
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Instead of regulating flow, it releases surges of water, accelerating erosion and forcing the creek to cut deeper into its banks.
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The upstream detention pond is overflowing, sending excessive water into Lyon Creek and eroding the banks of all three properties.
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Mark Gareys parcel is on the corner noted by the yellow arrow.
Cedar Way Dam upstream from proposed development
Mountlake Terrace Detention Pond view when not flooded
March 16, 2025 Video taken when it is not raining. Vantage point from filming north to south from 44th street. Mark Garey's property is in viewing range.
Notice the cage free of water
From the top of the cage is likely 10-12 feet down the bottom of the hill. The next pictures shows the entire hill filled in with water. Do you see the cage?
The cage if covered and flooded
The water runs quickly down the hill to Lake Forest Park, Mark Garey's property. The water doesn't top at the property line as FEMA shows. This pictures from the City of the Mountlake Terrace.
FEMA Flood Map
The map has a teal color shape highlighting the flood zone. You will notice it ends exactly on the border of Lake Forest Park. However, Mountlake Terrace is higher in elevation, so it is not logical that all of the water would stop promptly at the border. Gravity pulls the water downhill to Garey's property.
Flooded Drain on Garey’s Property
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A storm drain on the Garey property, meant to handle runoff, is failing to drain properly and is flooding instead. This suggests the property’s water management system is overwhelmed, contributing to instability.
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A storm drain on Mark Garey’s property is backing up, flooding the area and worsening soil saturation.
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Corner of 205th St and Cedar way, Dec 27, 2022
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This is the north side of the property where the water enters the property.
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Across the bottom street, Cedar Way/44th, you can see the water pooling, yet it hasn't rained that much. Look at the photo below.
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Picture that is across the street about 25 feet from the Garey Property from the above picture.
March 16, 2025 There hasn't been much rain, yet look at this large puddle. Garey's property elevation drops lower than the road.
Rapid Erosion: November 16, 2021 - January 7, 2022
Just under 2 months, Lyon Creek dramatically changed, eroding its banks and shifting closer to structures on all three properties.
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Visual Organization:
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Left Column → 1 Mark Garey’s Property (proposed house site)
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Middle Column → 2 Jang’s Property (my house)
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Right Column → 3 The Downstream Neighbor’s Property
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Markers to Track Changes:
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Point A & Point B: Vantage points for key before-and-after images.
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The creek is flowing from left to right, 1 to 3
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Below look at the purple shaded area. The steep slope flanks the westside of the creek . The creek is cutting into the bank, eroding the the vegetation making it vulnerable to landslides. The proposal report states the slope is 5%, which means almost flat. In another part of the proposal it states it is 30%, which is inconsistent and incorrect. You can visit the pics and videos below to see how the creek is cutting into the steep slope and caused the tree to slide and fall over.
Infrastructure Risks: Culverts & Downstream Impacts
On the previous layout of the 3 properties on the top right you will see a sign for the downstrem culvert. Below are pictures. The creek’s rapid changes put key drainage infrastructure at risk:
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Upstream Culvert– As erosion continues, this culvert may become blocked or collapse, disrupting water flow further.
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Downstream Culvert – More sediment and debris are being washed downstream, and the culvert has a lot of debris stacked up. Typically the water level at this culvert is 8 feet below the road. In the last few years, it has been 12-18" below the road. In the last 20 years, the water has flooded over Cedar way. Flood risks are high.
Culvert 2021 - see the debris
Culvert 2022 - see how close to the road
If the erosion, flooding, and infrastructure failures continue, the risks to all three properties will escalate:
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More land loss due to erosion
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Potential slope failure and property damage
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Increased flooding and stormwater runoff issues
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Compromised infrastructure (culverts, drains, and stormwater systems)
Culvert 2022 After the rains
Before the rain and snow
This is a typical day in November 26, 2021 before flooding. This is from vantage point A looking at property #1 notice the width of the creek and the immediate tree that is currently standing and alive holding up the west slope.
After the first rain
December 11, 2022 The banks are now flooded and this is just the beginning. In my 22 years of living here, I have never seen the creek so wide. The snow and rain hit us hard in Seattle from December 25 until January 7, 2022 causing 6 trees to fall because of the flooding of the creek on these 3 properties. This impacts the safety of these 2 houses #2 and #3 who live on the top of the slopes. If there was a house #1 was constructed, not only would they be subject to flooding, landslide, but the trees may also fall on their house.
Timber! The first of many trees falls down
December 25, 2022 With all of the flooding, the tree above in the video was uprooted because the water was raging and toppled this 30ft tall tree. Luckily, the was no house down there, so it didn't fall anyone. However, the property up above is endangered because of the slope erosion.
Examine the flow and you will see later how the creek widens
After the snow - the next day
January 2, 2023 I have never, ever seen the Lyon Creek so full. What is going to happen when all the snow melts?
After the snow and rain - banks are overflowing
January 7, 2022 The width of the creek has widened 300% and creek has risen up 5ft . This water on property #1 is draining properties on the top of the hill of 205th, the water from Mountlake Terrace from 44th and Lyon Creek. Can you imagine how this is hitting the slope and washing away the bank the holds up a house on top. Now there is no tree to hold in the slope. Plus disrupting the gravel and leaving silt everywhere making it unfriendly to salmon.
Listen to the creek, its much faster, taller and wider.
As you look downstream, Lyon Creek is flooding
Look at the increased width of Lyon Creek
January 7, this perspective is walking on 37th on property 2 walking towards property 3. Look at all the trunks of the trees submerged. All those blue cylinders with new plants are also underwater.
Holy Flooding!
The rain without better drainage and increased impervious services and more cut down trees, it will only get worse.
Timber again!
January 7, this tree about 12" width and approximately 30' fell over the road. Fortunately, no one was hurt. 5 more other trees fell too. We are lucky no pedestrians and cars were crushed. Many people walk their dog and jog along 37th. A couple of years before this, and alder tree fell over due the flooding. Many more tall trees may be dislodged and fall over, this is a hazard.
Notice the blue cylinders in the background. King County Conservation District is working with the neighbor to secure the slope and to nurture Lyon Creek by repairing the riparian zone along the stream.
Lots of trees fell over the culvert in the background that is under the concrete barrier. Normally, the water level is 5 feet lower than it is in the picture.
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On the 3 parcel map, this is on property #3 culvert.
Timber! Timber! Timber! Timber! Timber!
We have a flooding problem, lets consider safety first before we let a developer endanger human lives. Take a look at this video to all the trees trunks submerged in water. When it floods more trees will crash down and it might be on the road of the potential house.
Timber! Timber! Timber! Timber! Timber!
We have a flooding problem, lets consider safety first before we let a developer endanger human lives.
Flooding from north to south
In the summer, sometimes, it is hard to see any water. Look at high velocity flow for a normally tiny brook.
Count how many trees are vulnerable to fall down because their roots are getting saturated
Let's take another look at the tree that held up the steep slope
We have a flooding problem, lets consider safety first before we let a developer endanger human lives. Can you see why a neighbor might be conserved about their safety? The next house is the slope too. The tree that fell on the property #1, holds up house #2. What would you do if a builder proposed a house that allowed him to disregard safety hazards and to damage the environment?
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In the SEPA Checklist, the applicant says there is soil and no erosion on the slope.
Can you see why a neighbor might be conserved about their safety? The next house is the slope too.
