Yauger Park: The 6-Million-Gallon Machine Hiding in Plain Sight

The Hook: A Park Designed to Drown

Image Credit: Reddit u/CoverSad9809

As another “atmospheric river” slams into the Pacific Northwest, bringing inches of rain and the threat of catastrophic flooding, most eyes are on the rivers: the Deschutes, the Nisqually, the Chehalis. But in the heart of West Olympia, hidden directly behind the mesmerizing concrete curves of a popular skate park, a massive invisible engine is roaring to life.

Yauger Park is not just a place to kickflip or walk your dog. It is a massive Regional Stormwater Facility masquerading as public green space. It is the primary defense line for 150 acres of impervious concrete—specifically the sprawling Capital Mall complex—preventing that toxic, oil-slicked runoff from destroying the delicate ecosystem of Black Lake.

To the casual observer, the ponds look full; often dangerously so. To an engineer, the system is performing a complex hydraulic ballet, managing millions of gallons of water using gravity, biology, and 30,000 cubic yards of strategically excavated earth. The image above, captured by a local resident during a previous historic storm event, serves as a textbook example of the system at near-capacity, doing exactly what it was designed to do: hold the line.

*Video Credit: OLYTV3 (City of Olympia Official Channel)*

Technical Deep Dive: The “Hybrid Wetpond-Wetland”

The core technology at Yauger Park is what civil engineers call a Hybrid Wetpond-Wetland System. It is not a simple hole in the ground (a detention pond); it is a multi-stage water treatment facility designed to mimic the filtration capacity of a natural estuary, but condensed into a high-efficiency urban footprint.

1. The Inlet and Forebay: The Kinetic Brake

Water enters the system from the surrounding commercial highlands (Cooper Point Road and the Mall). It doesn’t just splash in. It hits a Forebay.

• Function: Energy dissipation and sediment settling.
• The Physics: As water rushes in from storm drains, its velocity is high, carrying heavy loads of sand, tire particles, and trash. The forebay widens the flow path, drastically reducing velocity ($v$). According to the continuity equation, as Area ($A$) increases, Velocity ($v$) drops: $Q = A \cdot v \rightarrow v = \frac{Q}{A}$ This rapid deceleration allows heavier particles (specific gravity > 2.65) to drop out of suspension via Stokes Law before they can clog the sensitive wetland plants further downstream. The forebay essentially acts as a “mud trap,” capturing the worst of the urban runoff.

2. The Cells: A Biological Reactor

The water then moves into a series of wetland cells. This is where the “Tech” meets biology.

• Capacity Calculation: The project involved roughly 30,000 cubic yards of excavation.
  • $30,000 \text{ yd}^3 \times 27 \text{ ft}^3/\text{yd}^3 = 810,000 \text{ ft}^3$
  • $810,000 \text{ ft}^3 \times 7.48 \text{ gallons/ft}^3 \approx 6,058,800 \text{ gallons}$
  • The Scale: This facility can hold over 6 million gallons of storm surge at peak capacity. That is equivalent to roughly 9 Olympic-sized swimming pools of contaminated water sitting just yards away from a residential neighborhood.

3. The Outlet: Gravity as the Pump

There are no mechanical pumps at Yauger Park. The entire system relies on a precisely graded hydraulic head. Water flows from cell to cell via gravity, eventually passing through a flow control structure that limits the release rate into Black Lake Ditch. This mimics the natural hydrology of a forest, releasing water slowly over days rather than hours, preventing the “flashy” flows that cause downstream bank erosion.

The Biology of Filtration: More Than Just Weeds

While the excavators built the container, the plants do the actual work. Yauger Park utilizes a specific palette of Pacific Northwest native hydrophytes, essentially turning the park into a localized wastewater treatment plant.

The Plant Palette

The system relies on robust species that can survive both drought (summer) and inundation (winter):

• Slough Sedge (Carex obnupta): The workhorse of PNW wetlands. Its dense root mats are exceptional at trapping fine sediments that escape the forebay.
• Hardstem Bulrush (Schoenoplectus acutus): These tall, reed-like plants provide surface area for periphyton—a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus—to attach.
• Small-fruiting Bulrush (Scirpus microcarpus): Adds biodiversity and further root mass.

The Mechanism: Phytoremediation

The plants don’t just sit there; they actively remediate the water through three primary mechanisms:

1. Rhizofiltration: The roots physically trap suspended solids.
2. Phytodegradation: The plants release enzymes that help break down complex organic pollutants like Polycyclic Aromatic Hydrocarbons (PAHs) found in oil and gasoline.
3. Nutrient Uptake: The plants absorb dissolved nitrates and phosphates (from fertilizer runoff) to fuel their growth, effectively stripping these eutrophication-causing agents from the water before they reach Black Lake.
4. Microbial Symbiosis: The most critical work is done by bacteria living on the plant roots. These microbes consume the hydrocarbons, converting toxic oil runoff into harmless byproducts like carbon dioxide and water.

Contextual History: The Black Lake Crisis

Why build a 6-million-gallon sponge next to a skate park?

In the late 1990s and 2000s, Olympia faced a reckoning. The rapid development of the Westside—specifically the “impervious surface” explosion of malls, auto rows, and parking lots—had broken the natural water cycle. Rain that used to soak into the ground was now flash-flooding into Black Lake, carrying a cocktail of:

• Zinc: Leaching from galvanized roofs and tire wear.
• Copper: Sheared off from brake pads every time a car stops at a light.
• Petroleum Hydrocarbons: Dripping from thousands of crankcases.

Black Lake was choking. Algae blooms were becoming common/toxic. The city needed a retrofit solution that didn’t just “store” water but cleaned it. The traditional solution would have been a massive underground concrete vault—expensive, ugly, and offering no community value.

Instead, the city opted for a “Green Stormwater Infrastructure” (GSI) approach. Yauger Park, a low-lying area, was identified as the perfect point in the basin. The renovation (completed around 2010-2011) was a massive civil engineering undertaking. It required moving earth on a scale rarely seen for a “park project.” The result was a dual-use facility: recreation on the dry days, critical infrastructure on the wet ones.

The Maintenance Reality: It’s Not “Set and Forget”

One of the biggest misconceptions about green infrastructure is that it is self-sustaining. It isn’t. An engineered wetland is a machine, and like any machine, it requires maintenance.

The Sediment Cycle

The forebay is designed to fill up. Every 5 to 10 years, depending on storm severity, the city must bring in heavy equipment to dredge the accumulated “muck.” If they don’t, the forebay loses capacity, the velocity doesn’t drop, and the sediment blasts into the wetland cells, smothering the plants.

• The Cost of Cleanup: Dredging a facility of this size is a major operation, often costing hundreds of thousands of dollars in mobilization, testing (the sediment is often classified as hazardous waste due to the pollutants), and disposal.

Vegetation Management

If the cattails and balrushes grow too thick, they can create “short circuits”—paths of least resistance where water channels swiftly through the vegetation without being treated. Conversely, if invasive species like Reed Canary Grass take over, they can choke the system entirely. City crews must monitor and manage the “green machine” to ensure it operates at peak hydraulic efficiency.

Analysis: Green vs. Gray Infrastructure

How does Yauger Park compare to the traditional “Gray” solution (concrete vaults and pipes)?

Feature	Yauger Park (Green)	Concrete Vault (Gray)
Capital Cost	Lower (Check specific project data, typically 20-30% less)	High (Concrete is expensive)
Maintenance	High (Vegetation, dredging, invasive species)	Low (Vactor truck pumping)
Lifespan	Indefinite (Self-renewing if maintained)	50-75 Years (Concrete degrades)
Co-Benefits	Wildlife habitat, recreation, cooling effect	None (It’s buried)
Adaptability	High (Plants adapt to climate)	Low (Fixed volume)

The “Green” approach wins on capital cost and community value, but it imposes a perpetual “gardening” tax on the city’s Public Works department. It trades upfront concrete costs for long-term labor costs.

Forward-Looking Analysis: The Atmospheric River Test

The design standards of 2010 are being tested by the climate reality of 2025.

The “New Normal” of Hydrology

Civil engineering uses “return periods” (e.g., the 100-year storm) to design infrastructure. However, atmospheric rivers are compressing these timelines. A “100-year storm” is happening every 5 years.

• The Challenge: If the incoming flow rate ($Q_{in}$) exceeds the design capacity of the forebay and the flow control structure ($Q_{out}$), the system enters “bypass” mode.
• The Risk: Bypass means untreated water hits Black Lake. During the current atmospheric river event, levels at Yauger are pushing the limits of the design. The photo from u/CoverSad9809 (captured during a separate, past event) illustrates what happens when the system nears its “emergency spillway” capacity.

Resilience and Adaptation

Yauger Park proves that Green Stormwater Infrastructure (GSI) is more resilient than “Gray Infrastructure” (concrete pipes).

1. Self-Healing: The biological elements (plants) grow back and adapt to changing water levels.
2. Scalability: The “cells” can be dredged and replanted to improve efficiency without rebuilding the entire park.

As cities like Olympia face wetter winters, Yauger Park stands as the proof of concept. We don’t need just bigger pipes; we need smarter parks. Places that invite us to play when the sun is out, and save our homes when the sky opens up.

Next time you drive past the skate park on Cooper Point Road, look at the “swamp” in the back. It’s working hard right now so you don’t have to swim to the grocery store.