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Rancho Ortega Blog discusses matters of public interest in South Orange County, including the communities of San Juan Capistrano, Ladera Ranch and Rancho Mission Viejo.

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The Role of Sienna Botanica Riverine System and the Horno Water Quality Basin in the Ladera Ranch Ecosystem

Residents of Ladera Ranch have noticed the construction work underway in the greenbelt along Sienna Parkway.  This two and a half mile long greenbelt starts in northern Ladera Ranch near Town Green Park and ends south of the community near Covenant Hills.  The riverine system is home to a meandering walkway along a man-made creek bed, complete with bridges, dotted by pocket parks and shaded by mature tree canopies.  What many people don’t know is that this greenbelt, officially called the Sienna Botanica Riverine System, is a sophisticated ecologically friendly water filtration system that carries community water runoff down to Horno Water Quality Basin while filtering out much of the man-made pollutants along the way.  Some of that water is recycled and returned to the community for use in irrigation, while the remainder flows out into the Pacific Ocean.  Silt filtered from the runoff water is deposited in the Sienna Botanica swale and from time to time, the system needs maintenance.  It is the removal of the silt and the re-grading of the swale that workers are doing now.  The system is all the more impressive when you consider the alternatives.  Absent a bio-filtration system like Sienna Botanica, cleaning runoff water requires either a chemical treatment plant or the decision to allow all of those pollutants to flow into the ocean.

Sienna Botanica Riverine System, as viewed from Sienna Parkway. (Image credit: Google Maps Street View)

Before the development of Ladera Ranch, this filtration process was performed naturally by El Horno Creek.  When homes and streets replaced the natural creek system, the Sienna Botanica Riverine System was designed to fulfill the same environmental purpose in a similarly natural way.  Residents might not realize the function of the Sienna system because the natural looking greenbelt hides a complex system of inlets, pipe and flow interceptors that regulate how much water can enter the creekbed.  In addition, there are 100 miles of buried French drains that collect water from Ladera’s many canyons and return that water to the system as well.  Once there, the water flows slowly downhill — the system was designed on about a 1% grade, so the water moves at a trickle.  Because Ladera Ranch is built on hilly terrain, that near-flat grade was achieved by building terraces connected by “drops” — man-made waterfalls, if you will.  Once the water completes its journey down the riverine system at its end point near Covenant Hills, the filtered water is allowed to flow into the Horno Water Quality Basin, first by entering a silt-collection holding bay and then by flowing through three settling ponds.

Horno Water Quality Basin (original image credit: Google Maps)

After the water leaves the settling ponds, the Santa Margarita Water District has the ability to pump some of that water back up into two reservoirs for reuse in the community.  Where are those reservoirs you ask?  Under Mission Hills Park in Covenant Hills.  When your kids are playing on the playground equipment there, they are on top of the recycled water reservoir.  And when you are using the putting green at Mission Hills Park, you are standing on the top of the domestic water reservoir.

Overhead View of the Two Underground Reservoirs at Mission Hills Park in Covenant Hills, Ladera Ranch (image credit: Google Maps)

The water that is not pumped to the reservoir for irrigation is allowed to continue down El Horno Creek as it joins the larger San Juan Creek system until it ultimately flows out into the Pacific Ocean at Doheny State Beach.  Much of the information in this article came from the “Focus on Ladera Ranch” video entitled “Up the Creek.”  Unfortunately, the video does not permit embedding, but it is a short and very interesting look at Ladera’s sophisticated and natural water bio-filtration system.

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