Guide to San Francisco Bay Area Creeks
The Urban Dweller's
Guide to Watersheds
Thinking Like a Detective in the Urban Landscape
by: Christopher M. Richard and Janet M. Sowers
Reprinted from California
Coast & Ocean
Wherever you are on earth you are in a watershed. Practically speaking, the watershed is the most useful unit for land
use management and conservation actions of all sorts: it follows the way nature organizes and divides the landscape. Beyond that,
finding your watershed, even in an urban environment, seems to be a very good pathway to deeper understanding of your place in
the world and where it is you call home. The more you study watersheds, the more you see the many ways that life and the land
Just what is a watershed? It's is the portion of a landscape that drains to a particular stream, river, or other
body of water. If rain falls on saturated soil, it will run off downhill. Runoff from all the hillsides in a watershed
eventually will reach the stream or river for which the watershed is named. For example, the American River watershed
is the area between the western ridge of the Lake Tahoe basin and Sacramento; any rainfall will run off into the American River.
Across the ridge to the north of this watershed is the Yuba River watershed; across the ridge to the south is the Cosumnes River
watershed. Of course, just as the American River is a tributary of the Sacramento River, the American River watershed is part
of the Sacramento River watershed. Most watersheds are part of a larger watershed and, in turn, can be subdivided into smaller
The boundaries between watersheds are called divides and generally follow ridge crests. The Great Divide, along the crest
of the Rocky Mountains, separates waters flowing to the Atlantic Ocean from those that flow to the Pacific.
If you live in a city or an urbanized area, you may need to think like a detective to discover your local watershed.
Many creeks have been confined to underground culverts beneath streets and buildings. Although many bigger creeks remain open,
they may run in concrete flood-control channels that bear little resemblance to natural creeks. Still, these altered creeks
define your watershed.
The best tool for discovering your local watershed, and your place in it, is the umbrella. On a rainy day, start on your
front steps; follow the rainwater down across the sidewalk and into the gutter. Which way is the gutter running? Follow it.
Soon you will come to a storm drain. This is where the game gets interesting. Maybe the water just flows back out of a storm
drain across the intersection, or maybe it falls into a culvert. Watch out for traffic, and peek down the drain with a flashlight;
which way does the water run? Look around; is there an apparent downhill? That is probably the direction the culvert runs,
typically under a street. Follow it and listen at each storm drain for the sound of water. Keep following the sound.
Remember that you are following a storm drain, not a sanitary sewer. Look for manhole covers that say "storm drain,"
not "sewer," unless you are in San Francisco, or parts of Sacramento, where the two are combined. With skill, and some luck,
you will find the point where the storm drain spills into a creek. The creek's name is frequently stenciled on the bridge
where the road crosses the creek. The name of that creek is the name of your watershed.
In hilly areas, simply walking downhill is a reliable way to find your local creek -- the creeks are in the bottoms of the
canyons or valleys. But if you live in a flatter area, such as the flatlands of Fremont or along the floors of the San Fernando
and San Gabriel Valleys, you may get fooled. In these areas the creeks built natural levees and actually run across the high
points on the landscape.
Next, find the divide surrounding your watershed. It will be a high point, although in flatlands the difference in elevation
may be barely visible. Back at the gutter, walk upstream from your house. Eventually you will come to a spot where the water
pools in the gutter. Farther still, the water in the gutter begins to flow in the opposite direction; there, you've crossed
your watershed boundary.
Now you will understand where you are in relation to the land and water immediately around you. It's only the first step,
for your little watershed is part of a bigger watershed, and so on. But at this point you may understand a few things that
may have mystified you earlier: why water seeps through a neighbor's basement every winter, for instance. That neighbor's house
may be standing over a culverted creek, or just uphill from one, in the path of groundwater flowing toward the former creek.
Ironically, an open creek might have drained this groundwater – the culvert may be preventing that drainage.
The umbrella is the best tool in your watershed quest, but it's by no means the only one. Look for a line of trees,
in Spanish, an alameda. Alameda County was named for the rows of trees that followed the creeks from the East Bay Hills,
proceeding across the flatlands and down to San Francisco Bay. Many of these rows of trees still cut across the urban landscape,
even where the creeks are today buried in culverts. In northern California these trees are frequently maples, redwoods,
eucalyptuses, and willows; in southern California look for sycamores, cottonwoods, and willows.
There are other clues you can look for. Traveling along many large suburban boulevards, you may be crossing creeks,
or the flood-control channels they have become, without ever noticing, for the crossings do not look much like bridges.
But if you see short stretches of matching high-security fencing on opposite sides of the street, that's a clue. Such fencing
is frequently erected to discourage junior hydrologists from chasing water striders in what remains of the creek
flowing under the road.
Maps are a great help, of course; several types are useful. California State Automobile Association (AAA) maps do a good
job of showing remaining urban creeks in northern California, but sadly, the same is not true in southern California. Even
the northern California AAA maps are not without oddities, such as creeks and roads "rerouted" around the map legend or street
index. The U.S. Geological Survey topographic maps are great, especially in less developed areas. Creeks are clearly marked;
ridge-crest divides between watersheds are also evident. But topo maps are often out of date because, typically, the urban
landscape has been altered since the map was produced. Take a blue marker and highlight the fine blue lines that represent
creeks on the map showing your neighborhood. Then, walk around your neighborhood double-checking what they show. You'll
probably find lots of differences.
If the map you are using shows few actual creeks, still other clues await you. A street that wiggles across the map with
little alignment to the local street grid may be built over or alongside a culvert laid in a creek. Glendale Boulevard,
Laurel Canyon, and the Pasadena Freeway in the Los Angeles area are all good examples, as is 14th Avenue in Oakland.
To get a detailed picture of the storm drain and creek system in a region, you need the storm drain maps from city and
county public works departments. These maps show block-by-block detail of storm drains, and usually the creeks as well.
However, even if your local agency has done a good job of mapping, the maps may be incorrect. Most agencies record only
culverts they build themselves or for which they issue permits to contractors. Culverts built without permits seldom appear
on these maps. Sometimes culverts were not built show up nonetheless on the map because a permit was issued. Where creeks are
the borders between counties, culverts may not be recorded by either county.
Another great resource is old maps. They show the creeks before your neighborhood was built. Central libraries and university
libraries often have map rooms or history rooms with maps of the Spanish land grants, government survey maps from the 1850s,
or real-estate maps from the turn of the century. Aerial photos may be available as well. These are all treasure troves,
rich sources of further information to help you understand your watershed.
So there's a start. Locating your creek and watershed in an urban environment can be a challenging task, but it can be
eye opening. If you're lucky, you may live in an area where someone has published detailed creek and watershed maps. These
are great tools for your quest, but they are no substitute for actually going out with your umbrella to follow your runoff.
You will see how this water, hidden and confined, still nourishes plants and wildlife, and come to appreciate the direct
connection between your home and the natural world.