Archive for the ‘Oakland streams and water’ Category

Oddball Lake Merritt

16 September 2019

Oakland has several major, permanent streams crossing it from the hills to the Bay. Then it has Lake Merritt, formerly known as San Antonio Slough — an arm of the sea extending more than a mile inland from the shore.

What makes it so exceptional?

I have a theory, based on the last million years or so of geologic history plus some of the latest research.

First of all, we need to ignore the Lake Merritt we know today:

. . . and think of Oakland as it originally existed. This is an excerpt from the “Bache map” of 1857, a survey of the waters surrounding the newborn city of Oakland and its neighboring town of Brooklyn painstakingly made by the U.S. Coast Survey. It covers the same area as the Google Earth clip above. It’s a fat 1200-pixel image worth zooming in on (or study the full-size scan from Wikipedia).

“San Antonio Creek” was the inlet that led to the existing landing at Brooklyn. It had a central channel, just a couple hundred yards wide, that was deep enough for ships, and the rest was tidal mudflats or treacherous shallows. The slough extending to the north — today’s Lake Merritt — had strong tidal currents and a very shallow mouth. Small craft could use it when the tide was high, and duck hunters were a common presence there, but for serious commerce it was useless, and Oakland’s landing at the foot of Broadway was little better.

Back then, San Antonio Slough had a wider mouth lined with wetlands, with terraces roughly 25 feet high on either side. Later the mouth got filled in leaving the narrow passage we know today . . .

. . . but if you look for it, for instance down 10th Street past the museum and auditorium, you can get a sense of its original width.

My theory starts with taking the mind back into recent geologic history — the dozens of ice ages that have occurred regularly for the last 2-plus million years. When the ice caps were at their largest, the sea sat hundreds of feet lower than today. Except for the Golden Gate itself, the whole Bay was dry land, and all of our creeks ran out far beyond today’s shoreline to join the combined Sacramento-San Joaquin River. Today’s Lake Merritt, then, is a drowned stream valley — a term east coast geologists know well, but seldom used around here.

For clarity’s sake I will use the name Merritt Creek for the stream that occupied that valley during glacial times. Glen Echo Creek ran into Merritt Creek down a swale where the north arm of Lake Merritt sits today.

The eastern arm of today’s lake was where three creeks joined: Pleasant Valley, Wildwood and Indian Gulch (Trestle Glen) Creeks. You know, let’s call the drowned valley Pleasant Valley, because it surely was one. The late Pleistocene creatures and vegetation there I will leave to your imagination.

Three more smaller streams also drained into Merritt Creek: “Kaiser Creek” at 20th Street, “Adams Point Creek” at Perkins Street and Park Boulevard Creek at the E. 18th Street landing.

Here they all are on the watershed maps from the Alameda Country Flood Control District.

And if you adjust this map in your mind by subtracting the sea, Merritt Creek also received input from 14th Avenue and 23rd Avenue Creeks (that is, the rest of San Antonio Creek).

My argument is that Merritt Creek is a drowned valley today, instead of an ordinary creek like the rest of Oakland’s streams, because it cut down deeper than other creeks. I can cite three reasons for that.

First, Merritt Creek had the largest watershed between San Pablo and San Leandro, thus it had the greatest water-gathering power in the area — especially during glacial times. And as the watershed map shows, the stream network is well organized, capable of delivering stormwater in a big flush. It didn’t dribble across a wide coastal plain like Temescal and Sausal Creeks on either side. Whereas those creeks spread out their floodwaters on the plain and slowed their flows (depositing their sediment across the landscape), Merritt Creek was confined between elevated banks and couldn’t slow down. It was better equipped to cut into the exposed floor of the Bay.

Second, Merritt Creek drained a large area of hard bedrock: the Franciscan sandstone, shown in blue on the geologic map, that underlies the hills of Piedmont. I argue that this substrate didn’t generate as much mud or clay as its neighbors and made the stream network less prone to clogging.

Third, unlike Oakland’s other major streams, Merritt Creek’s watershed didn’t cross the Hayward fault and was not affected by it. This is an intricate subject I plan to address in future posts as well as my book. Briefly, the fault messes with streams as its sides slip past each other. Headwaters in the hills get slowly cut off from their downstream reaches. Streams get stretched and snap, interrupting their natural evolution into well-organized networks like Merritt Creek’s. The head of one stream gets grafted onto the stem of another stream, and the transportation of sediment from hill to bay — the basic function of streams — is stymied and randomized.

Maybe this argument is easier to read in a simple image, a shaded digital elevation model of central Oakland. The fault line is obvious, as is the integrity of Merritt Creek. Temescal and Sausal Creeks reach around Merritt Creek’s drainage, like hands holding a bowl, and cross the fault with disruptions you can explore on the AC Flood Control District site.

Another more scientifically phrased argument was just published in the journal Earth Surface Processes and Landforms. The paper is based on the example of the Dead Sea, where human intervention has been lowering the world’s saltiest lake. A team of geologists took that as an analog of the glacial cycle and asked how the streams feeding the Dead Sea have responded. The bigger, wetter streams cut down into the land, keeping up their deliveries of sediment as the water recedes, while the piddly streams give up and stay behind. Reading the abstract, I immediately thought of our creeks and the exceptional one whose drowned valley is, for the moment, our little mediterranean sea, our miniature San Francisco Bay, named Lake Merritt.

You know how the Pleistocene was, full of large beasts that have slouched off into extinction: mastodons, giant ground sloths, sabertooth cats, dire wolves and so on. There were monsters around then.

And today we have three monsters around the lake. Have you seen them? The newest one is named Makkeweks, inspired by Ohlone stories, and lives in Snow Park.

Makkeweks joins the newly restored Mid-Century Monster (here as seen in 2005) . . .

. . . and the original, the one and only Fairyland Dragon.

Think of the Pleistocene when you visit them.

Stream surgery in Dimond Canyon

26 November 2018

Last week was a treat, as the long-awaited start of the annual rains cleared away the thick smoke from the distant Camp Fire. On Tuesday, the air still smoky, I took an afternoon to check in on a few of our streams at their dry-season minimum. Then on Saturday I came back. In Dimond Canyon Park, the new improved Sausal Creek was especially impressive in its reawakening.

In truth, it was never asleep. We did cosmetic surgery on it without anesthesia. Now, as the rainy season proceeds, we need to watch the bandages.

Sausal Creek has had a lot of work done in Dimond Park. The streambed in the park proper, west of the swimming pool, was cleaned out in 2015 and planted in willows — fitting for a creek of its name. In just two rainy seasons, they’ve grown at a prodigious rate.

Now the stream is mostly hidden, but that’s good. To be pleasing for fish, the water needs shade — that keeps the water cool, able to hold more oxygen — and the new thicket keeps out most of the people and their dogs (although I did see a housecat perched on the rocks).

On Tuesday there was precious little water there. It was like everything was holding its breath.

Saturday I could hear the water long before I saw it. A wonderful sound. Even the sterile new section, built after daylighting a stretch that was culverted in 1952, felt like it was ready to burgeon.

Here, just downstream from El Centro Avenue, I could walk up the streambed on Tuesday. . .

. . . but not on Saturday.

The latest surgery is higher up the stream, in Dimond Canyon proper. It involves three watershed wounds, carved by undesirable runoff from the streets around the canyon. Too much sediment washes into the creek for the rainbow trout who live there (I had no idea they’d survived all this time).

Remediating the effects of heavy runoff isn’t a job done by eyeball with a shovel and wheelbarrow. It’s work that calls for heavy equipment, done with surgical care and designed by geotechnical pros. It’s supposed to last as long as the land itself. It’s supposed to heal over with real vegetation and fool the wildlife.

At this site, the object is to keep runoff from carving a gully down the slope. When runoff is modest, it can soak through the channels of stones at the top left and trickle downhill gradually. In a heavier rainstorm, the channels will guide the water aside instead of dumping it all straight down.

The ground is covered with geofabric, a coarse burlap, and strewn with seeds ready to sprout and offer the slope more protection. More substantial native plants, like dogwood, will be added.

The most ambitious part of the project gave a makeover to a long gully reaching the creek from a street drain on San Luis Avenue. This is just the bottom end, below the Old Cañon Trail.

It was ugly. Now it’s raw — the work was finished in September. But it held up fine during last week’s rain, so far so good. The snag of tree roots in the front is meant to be there; dead wood is part of a thriving ecosystem. More shrubs will go along the streambanks where the stakes are.

This site is where the most hard-core work was done. A storm drain from the end of Benevides Avenue unavoidably dumps a lot of water here, so the site is strongly fortified without turning it into concrete.

The plastic pipe directs the runoff onto an energy-dispersing boulder pile. The pipe can be repaired as needed without tearing up the rest of the slope. And if you look closely you’ll see thin sticks standing around the outlet. Those whips are going to grow into trees.

On Saturday this too was a cheerful scene. Some of the whips are already showing leaves.

Over the next few years, let’s watch as the creekside patiently recovers. News, background info and opportunities for the public to help are all at sausalcreek.org.

A stroll up Indian Gulch, or Trestle Glen

28 August 2017

Once upon a time there was a thriving native encampment near the head of San Antonio Slough, tucked under bountiful oak trees in a valley with a permanent stream. Then the padres of New Spain put the natives behind walls to earn their bread with the sweat of their brows, and a generation later the Mexican rancheros converted them to secular laborers. The valley, which took on the name Indian Gulch after the Indians were gone, has remained significant. The property line between the lands of the Peralta sons, Antonio on the south and Vicente on the north, ran directly up its streambed.

On the map, the valley with its tributaries looks like a long feather, arcing across the bottom of this map from Lake Merritt (the former slough) into the hills of the Piedmont bedrock block.

Today the valley is an Eden of the suburban sort, well worth a walk for its natural and human sights. These sights do not include the stream, now called Trestle Glen Creek and mostly culverted or hidden in back yards.

The lowermost part of the valley, going up Trestle Glen Road, has a very gentle grade, taking well over a mile to climb 100 feet. The sides of the valley rise a good hundred feet on either side.

The stream here is at grade, meaning it has cut down about as far as it can. The ground it has eroded is the sediment of the Fan, not bedrock. See it here on the geologic map.

This stretch of the valley ends just past Norwood Street as we enter bedrock country.

The grade steepens slightly, and the valley walls close in a little. The power line towers in the back of this view sit on bedrock.

Two very unobtrusive footpaths lead from here to either side of the valley where you can encounter the bedrock. The one on the south side is particularly discreet; you might have better luck coming down from Park Boulevard via Elbert Street to see this exposure.

It’s your standard Franciscan metasandstone, the same stuff that was quarried in Piedmont before it incorporated in 1907. There’s also a nice exposure on Trestle Glen Road a little farther up.

By now the valley has gotten distinctly narrower and steeper. Right at the city line at tiny Valant Place, Trestle Glen Road leaves the streambed and climbs up to Park Boulevard. Seen from Valant Place, the valley is a real ravine now.

You can’t walk up the valley any farther; it’s all on private land. But from the Piedmont streets that flank the valley — Indian Road, La Salle Avenue, St. James Drive — you can catch glimpses of the living stream.

The Uptown to Montclair ramble I posted a few weeks ago goes through higher parts of Indian Gulch. But the longest stretch of the unspoiled stream, the western branch, is totally secluded in private hands. That branch is where the rancho boundary went. You can spot it from the 33 bus, on Hampton Street, if you know where to look.

So is this a glen, or is it a gulch? Both terms refer to small, steep-sided valleys with running streams in them. However, a glen is typically wooded — the word comes from the Gaelic — and implies a green, secluded place. A gulch not only has steep sides, but also a steep slope with a rushing mountain stream, and the word is widely used in the Southwest. A gulch is forbidding, but, especially in California, it’s well suited for gold panning. This valley offers both wealth and seclusion today, so I call it a toss-up.

Well water in use

21 August 2017

Once upon a time, we used to produce a lot of our water from local wells, but for the last century we’ve retired them as the aquifers were drawn down or polluted. So I’m always surprised and intrigued to see wells still at work. This is on Willams Street in San Leandro.

The location is a big educational complex comprising John Muir Middle School, San Leandro Adult School, and Woodrow Wilson Elementary. Presumably the well is for watering the grounds, not supplying the drinking fountains.

The water is a remnant of the once-productive San Leandro Cone, a body of sediment full of groundwater supplied by San Leandro Creek. The geologic map shows it as a set of fingers radiating from Lake Chabot, labeled “Qhl.”

Qhl stands for “Quaternary Holocene levees.” The Quaternary Period includes the last 2.6 million years of Earth history, and the Holocene Epoch is the final portion of the Quaternary, the time since the glaciers last melted. I think of the Holocene as the geological present.

Levees form when floods regularly spill over a riverbank — the moment rushing floodwater leaves the river, it slows down and immediately drops most of its sediment load. Repeat this enough times and a low rise builds up on both sides of the river: a pair of levees.

The map explanation says about Qhl, “these deposits are porous and permeable and provide conduits for transport of ground water. . . . Abandoned levee systems have also been mapped.” And that explains the well water of Williams Street — the street runs right down the middle of a former course of San Leandro Creek. Here’s a closeup.

The map shows that the Qhl unit coincides with an extremely gentle rise in the ground about 10 feet high and a quarter-mile across. Natural levees are rare to see, because humans build them up higher for “flood control,” but you’ll easily see the rise if you walk away from Williams Street a couple blocks and look back at it.

So San Leandro Creek once ran this way, must be thousands of years ago. Something perturbed it enough to cut a new streambed in another direction, and this abandoned course filled in. But it still carries water underground.

The northernmost finger of Qhl in the San Leandro Cone leads to the former site of Fitchburg, where a major wellfield once supported East Oakland with groundwater.