One of the most striking features of California geography to me is the proportion of streams that are not perennial. My upbringing was entirely in humid places, where anything regarded as a "stream" basically always had water in it, at least as far as I looked. But common in any arid place are intermittent or ephemeral streams—where water flowing over the surface is not a given.
For intermittent streams, water may come and go with the seasons. But In especially dry places, these streams become "ephemeral": the water comes rarely, and when it does, it often comes hard. A stream like this may be called a wadi, or an arroyo, or—my favorite, for its other English evocations—a wash.
The wash is crucial to the native ecologies around it, but it poses interesting problems to geomorphologists and engineers. In much of the earth sciences sciences, there's an expectation that landscape systems have some kind of "steady-state," a stable shape or behavior that systems tend towards, which realistically means some kind of dynamic equilibrium. Storms erode a beach, but then the waves and tides slowly build it back up; somewhere between lies a stable equilibrium. The timescales can be longer and more asymmetrical, however. Coastal landscapes respond to daily high tides; forests might respond to monthly wind storms; most landscapes are accustomed to yearly/seasonal change. As the extremity of the forcing events and the period between events gets larger, we must acknowledge that these systems have a "background" behavior that occasionally gets knocked out of sorts, rather than any kind of balance. Chaparral landscapes might have a prototype look and feel, but they are also built to burn every couple decades, after which they spend a year or two looking apocalyptic.
It is around this decadal return period that poses problems to civilization, because it's a timescale that humans don't seem to plan very intelligently for. Yearly is easy to remember (birthdays, seasons, holidays); to remember a once-every-20-years event becomes a task of generational or institutional knowledge. Consider: a huge flood happens, and people retreat from the river for a few years. Then we think, why retreat? The land is fertile and water is close-by if we live near the river. But the flood will come again, and some octogenarian in the back of the room will be yelling that they told us so.
There is a sort of fat tail, or "kurtosis" risk to humans lurking in any kind of landscape prone to sudden, rare, and dramatic events, like storms, fires, earthquakes, and floods; a complacency to the recurrent, but forgettably uncommon, disaster. For its relevance to water and the built environment, I find flooding the most interesting of these. My fascination lies interlinked with the time I spent living just blocks from where the Arroyo Seco meets the Los Angeles River in Northeast Los Angeles.
The Arroyo Seco and LA River are both channelized where they meet, which means that they have been paved over in concrete. In how I've learned to use the term "the wash," it's always in reference to one that's been paved over. Paving does a few things to the river: it fixes its geometry, preventing the river from moving across property lines and flood zones; it also makes the surface of the riverbed smoother, allowing the water to move faster. By accelerating the flow, the channel can carry more water and prevent nearby areas from flooding during heavy rains.
Channelization is (generally) a great flood-prevention strategy, but it has downsides. The concrete disconnects the river flow from its bed, preventing any of the river water from sinking into the aquifer beneath it; similarly, it prevents the river from depositing (or eroding) any sediment on the bed; these combined effects dramatically affect the physical and ecological processes in the riparian area. Accelerating the flow, and preventing any exchange between the water and the landscape brings a torrent of dirty water downstream. In Los Angeles, this all ultimately flows out to the ocean at Long Beach, and is the reason why LA-area surfers know not to go for an ocean dip within a couple days of a rain. The Tijuana River, along with most streams in Southern California, is also channelized, but it empties out into a "natural" green wetland area before it reaches the ocean: the fast-moving water from the channelized portion has the potential to rapidly erode the wetland, and dump all of the contaminants that it has collected on its route to its destination.
Despite channelization, life finds a way. And people do, too—the Los Angeles River is, perhaps, the most celebrated (in the sense of celebrity) flood control infrastructure on the planet. The whole city needs the wash to keep its role as a flood control measure, but some want to see it work as park, a social focal point, an ecosystem, too. Some like it as it is. Water flows downstream and life seems to follow it. Jenny Odell writes:
For intermittent streams, water may come and go with the seasons. But In especially dry places, these streams become "ephemeral": the water comes rarely, and when it does, it often comes hard. A stream like this may be called a wadi, or an arroyo, or—my favorite, for its other English evocations—a wash.
The wash is crucial to the native ecologies around it, but it poses interesting problems to geomorphologists and engineers. In much of the earth sciences sciences, there's an expectation that landscape systems have some kind of "steady-state," a stable shape or behavior that systems tend towards, which realistically means some kind of dynamic equilibrium. Storms erode a beach, but then the waves and tides slowly build it back up; somewhere between lies a stable equilibrium. The timescales can be longer and more asymmetrical, however. Coastal landscapes respond to daily high tides; forests might respond to monthly wind storms; most landscapes are accustomed to yearly/seasonal change. As the extremity of the forcing events and the period between events gets larger, we must acknowledge that these systems have a "background" behavior that occasionally gets knocked out of sorts, rather than any kind of balance. Chaparral landscapes might have a prototype look and feel, but they are also built to burn every couple decades, after which they spend a year or two looking apocalyptic.
It is around this decadal return period that poses problems to civilization, because it's a timescale that humans don't seem to plan very intelligently for. Yearly is easy to remember (birthdays, seasons, holidays); to remember a once-every-20-years event becomes a task of generational or institutional knowledge. Consider: a huge flood happens, and people retreat from the river for a few years. Then we think, why retreat? The land is fertile and water is close-by if we live near the river. But the flood will come again, and some octogenarian in the back of the room will be yelling that they told us so.
There is a sort of fat tail, or "kurtosis" risk to humans lurking in any kind of landscape prone to sudden, rare, and dramatic events, like storms, fires, earthquakes, and floods; a complacency to the recurrent, but forgettably uncommon, disaster. For its relevance to water and the built environment, I find flooding the most interesting of these. My fascination lies interlinked with the time I spent living just blocks from where the Arroyo Seco meets the Los Angeles River in Northeast Los Angeles.
The Arroyo Seco and LA River are both channelized where they meet, which means that they have been paved over in concrete. In how I've learned to use the term "the wash," it's always in reference to one that's been paved over. Paving does a few things to the river: it fixes its geometry, preventing the river from moving across property lines and flood zones; it also makes the surface of the riverbed smoother, allowing the water to move faster. By accelerating the flow, the channel can carry more water and prevent nearby areas from flooding during heavy rains.
Channelization is (generally) a great flood-prevention strategy, but it has downsides. The concrete disconnects the river flow from its bed, preventing any of the river water from sinking into the aquifer beneath it; similarly, it prevents the river from depositing (or eroding) any sediment on the bed; these combined effects dramatically affect the physical and ecological processes in the riparian area. Accelerating the flow, and preventing any exchange between the water and the landscape brings a torrent of dirty water downstream. In Los Angeles, this all ultimately flows out to the ocean at Long Beach, and is the reason why LA-area surfers know not to go for an ocean dip within a couple days of a rain. The Tijuana River, along with most streams in Southern California, is also channelized, but it empties out into a "natural" green wetland area before it reaches the ocean: the fast-moving water from the channelized portion has the potential to rapidly erode the wetland, and dump all of the contaminants that it has collected on its route to its destination.
Despite channelization, life finds a way. And people do, too—the Los Angeles River is, perhaps, the most celebrated (in the sense of celebrity) flood control infrastructure on the planet. The whole city needs the wash to keep its role as a flood control measure, but some want to see it work as park, a social focal point, an ecosystem, too. Some like it as it is. Water flows downstream and life seems to follow it. Jenny Odell writes:
I realized why it was so hard to define what a creek is. It’s not only that in some places it feels indistinguishable from infrastructure. It’s that a creek is just one form of water that needs to go somewhere, and water always needs to go somewhere.
I love the wash as it is, for all its flood-prevention utility; I hate the wash, for paving over tender soils; I love the wash, for its bizarre concrete shapes; I hate the wash, for causing us to lose so much of our precious water; I love the wash, for its drama and power in the arid landscape. We need to un-pave some of our urban environments, for the long-term sustainability of our groundwater and surface ecology, but the mythos of the wash will persist. The FOVICKS site states, "there simply is no going back to a dirt bottom river without removing the town around it."
Ian and I have been noodling on the architectural ramifications of water infrastructure for a little while, and the wash is a perfect candidate for further scrutiny. Is the wash conceptualized as a natural space? As infrastructural? (akin to a freeway overpass?) What else can it be? How do we experience its length and scale and variety? How do we aestheticize its vast concrete expanses and careful geometry, with grasses yet poking through? How is its value—or "revitalization" used as a tool for real estate valuation? How does it work, by itself and with the rest of the territory around it? Is the wash always downstream or upstream of something else? I prefer to think it can be a site of its own.
Intermittent,
Lukas