Tuesday, September 23, 2014

The Long Arm of Hurricane Norbert Goes to Work at Tucson Audubon's Ecosystem Restoration Sites

Most all of us in southern Arizona experienced first-hand the powerful remnants of Hurricane Norbert during that soggy second week this September. The steady and unrelenting rain led to flash flooding of highways, houses and everything else in its path, including Tucson Audubon's restoration areas in Marana and southeast Tucson.

Simpson Farm the day after the September 8th flood (Marana, AZ)

When the field crew arrived for work at our Simpson Farm restoration project near Marana on the morning of September 9th, they were greeted by a rare and sobering site: the Santa Cruz River, normally tamed and contained by man-made channelization and diversions along its entire course from Tucson to Simpson Farm, had flooded. Big time. Irrigation lines were tossed about at random, hulking debris piles stood against anything above-ground in neatly arranged Jenga-like stacks and, to the crew's dismay, dozens of meticulously planted and nurtured native restoration plants had been buried. Floodwaters had also re-contoured many areas of the site, carving out access roads and rendering them impassable in places, and completely filling in arroyos and depressions.

Field crew veteran Dan Lehman surveys the deluge at Simpson Farm

The Santa Cruz River receding from Norbert-strength at Trico Road,
 Marana, AZ. Simpson Farm begins on the other side of the bridge.

Stakes marking spots where native restoration plants
were planted in 2013-at ground level

Suddenly, a site that on average receives considerably less rainfall per year than Tucson had become a series of lakes. Despite the buried plants and general chaos that the flood created, we couldn't help but revel in this blessing of immense moisture--delivered free of charge by Mother Nature, irrigating better than we could ever hope to. As we carefully dug out our buried plants and realized that most of them were probably going to be just fine, our dismay turned to hope. As of September 22, the rare sight of standing water persists in many spots at Simpson Farm, and most of those buried plants look great.

The locals were out in full force after the flood: checkered
gartersnake at Simpson Farm. Dozens of newly hatched and adult
 Couch's spade-foot toads were also out enjoying the plentiful puddles.

Back in town, the leftovers of Norbert produced similar but thankfully less catastrophic flooding at our urban restoration project along Atturbury Wash.  The Atturbury Wash-David Lyman Nature Preserve is a narrow swath of intact desert wash ecosystem located within Lincoln City Park, near Davis-Monthan Air Force Base. This restoration project is a two-pronged endeavor combining dozens of stream restoration structures which increase on-site moisture and reduce channel incision with over 900 native restoration plantings to revegetate areas denuded by decades of off-road vehicles and heavy equipment use.

Demonstration area at Atturbury Wash in 2012,
before the project began

The same area in May, 2014

July, 2104
The stream restoration structures installed along Atturbury Wash and its tributaries are intended to work with the natural process of flooding, but every built object has its limits. The flooding from a 1.5" storm in late July coupled with the 2.5" that Norbert dished out in early September pushed some structures beyond their limits.

Gully-plug, unplugged

Boulder vane unraveling after flood

Despite the failure of some of the structures, most of them weathered the floods quite well and have performed admirably. We've watched incised and degraded channels aggrade (fill-in), have seen more moisture and increased vegetation along the washes, and, during two storms, have even witnessed Atturbury Wash itself flood over its banks and irrigate its water starved flood plain for the first time in quite a long time. Due to this flooding we've seen an unprecedented response from annuals like common sunflower (Helianthus annuus) and tansy aster (Macranthera spp.), as well as perennials like blue palo verde (Parkinsonia florida) and burroweed (Isocoma tenuisecta).

Tell-tale flood debris shows us that the Wash over-topped its
 banks and irrigated its floodplain

A one-rock dam, 1 of dozens at the site, successfully trapping
 sediment, slowing flows, and aggrading this tributary to
 Atturbury Wash

We were pretty concerned about one area of the site where an incised wash was threatening to cut back ("headcut") into the nearby hiking trail. The one-rock dam that had been initially installed to stop this from happening had failed in a flood last August, and the worst seemed imminent.

One-rock dam failing at headcut

So we set out to remedy the problem. Developed by stream restoration guru Bill Zeedyk after ancient farming structures on the Zuni Pueblo, a Zuni bowl creates an energy-dissipating plunge-pool that stops a head-cutting wash from progressing up stream and further degrading an area.

Zuni bowl under construction. That's our dependable volunteer
 Stuart Lueders on the right; he and another awesome and equally-
dependable volunteer, Bill Sievers, completed this Zuni bowl that day

The same structure going strong in September after 3
 major flood events, including Norbert's wrath.

None of our successes at Atturbury Wash would've been possible without the incredible help of 100s of volunteers over the past 2 years. We'll be holding 3-4 more volunteer events this season at the Wash, so please come on down to lend a hand and learn about stream restoration, native plants, and much more. You can check our Events Calendar or contact me for more information.

Hope to see you out there!

-Andy Bennett
Tucson Audubon Restoration Staff

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