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Abstract: Increased flooding frequency and intensity is being experienced all over the world at an alarming rate. Even the most prepared or "hard-engineered" cities are being caught by surprise when they find themselves submerged in flood waters. While it is easy to point a finger at changing temperatures and weather patterns, it is becoming more apparent that the way we have developed and planned (or not planned) our cities is the true culprit. In this post we can examine a recent flooding event in Mendoza, Argentina to reveal some background information on this pressing challenge and some possible solutions using the principles of Green Stormwater Infrastructure and plain common sense that may help mitigate this threat for the future of the city.
When it rains, it pours...and hails too
For those who may call the desert home, there is perhaps no event more beautiful, while at the same time threatening, than a summer rainstorm. The smell of the earth, ozone, and the hint of moisture on the horizon can awaken the senses and compel even the most unmindful to step outside for a moment in anticipation of this rare event. Occurring only a few days per year in some arid regions, desert rainstorms (also known as monsoons in the southwestern U.S.A or aguaceros or diluvios in Mendoza, A.R.) are characteristically intense and can drop a large portion of the annual rainfall in a matter of minutes. Such was the case in Mendoza on November 12, 2020.
What was expected to be rain turned into a violent hailstorm (locally know as granizo or piedras) followed by extreme flooding and overwhelm of nearly every drainage system, especially the acequias. Annually, Mendoza receives approximately 220 mm (about 8.5 inches) of rain, mostly in the warmer months of the year. According to the Diario de Mendoza, between 50-70 mm (about 25% of the annual rainfall) was counted in a matter of one hour due to this aguacero.
Images above: Hail accumulations turning Mendoza into a wintery scene within minutes. The sheer force and volume of the ice severely damaged many trees as it shredded their leaves. Worst of all, I had just cleaned the pool.
It was not long before signs of flooding began to show. Admittedly, I was very excited to finally have the chance to see just how Mendoza's acequias functioned as drainage during storms. Until this point, I had only heard about the overwhelm that tends to happen during rain events. Many people speak of the challenges with trash and debris that accumulate and can clog the waterways, which is a major pain point for managers when discussing the advantages of supporting the urban oasis in Mendoza. As you can see, the acequias are designed to function as irrigation systems as well as stormwater drainage, capturing the runoff from the roads through various curb-cuts. As we can see below, the intensity of this storm was too much and there seems to be more water still on the roadway than in the acequias.
Video above: Footage capturing the intensity of the storm. Audio just doesn't do it justice. Hail, rain, and debris are starting to accumulate rapidly on all surfaces.
Image above: Curb-cuts draining runoff from the roadway into the acequia.
Video above: Roadways draining to acequias. Even with abundant curb cuts, the runoff can't drain fast enough given the intensity of the storm.
Image above: Acequias clogged with trash and debris. Drainage spills back over into the streets causing deep standing water. The tree doesn't seem to mind the extra water.
Once the worst of the storm subsided, there was a flurry of activity outside our home, so of course I had to investigate. The first observation was the deep ponding at the end of the street where a police patrol was stationed. We are not sure if this was for supporting drivers as they went through this deep area or for the news crews that showed up an hour later in front of the house. Either way, we can see that the flooding is due to the acequia being overwhelmed and spilling into the street. As I made my way over to Juan B. Justo, a major arterial in the city, I saw what was more or less a temporary river engulfing the entire street including sidewalks. This same condition was observed throughout the city.
Image above: Acequias overflowing into neighborhood intersection. Police on standby for adventurous drivers.
Video above: Footage of flooding along Juan B. Justo inundating acequias and engulfing sidewalks too.
Video Above: Footage what seems to be a river running down one of Mendoza's most prominent avenues (Emilio Civit). Video credit: Diario de Mendoza
Video above: Violent waters in one of the City's several zanjónes/primary drainages. You can really hear the power of the water. Credit: Diario de Mendoza
Despite the shocking magnitude of the storm and subsequent flooding, the Mendocinos characteristically seemed to take it all in stride with a somewhat self-deprecating shrug of the shoulders indicating "such is life " and dash of humor as evidenced by the onslaught of memes that appeared to be be almost ready-made for just such a moment. As "normal" as they may seem to be here, at closer inspection there are some very clear signs that not only is our climate changing, but that we are affecting the severity of these events without even realizing it.
Meeting highlights with the Department of Irrigation
After witnessing just how bad the flooding can be in Mendoza, I was very curious to learn more about the problem and what kind of solutions, if any, are being developed to address it, especially what kind of conversations are bein had about the acequias. I had the great fortune of coincidentally connecting with the Department of Irrigation (Departamento General de Irrigación) soon after the event regarding other work, and took advantage to learn a bit more about water management in Mendoza.
Image above: Aerial map of the Mendoza province in the basement library of the Department of Irrigation.
Image above left: Author and Dra. Marcela Andino in front of the Department of Irrigation office in Mendoza. Image above right: Author getting a little publicity being the first civilian to meet in the office since the start of the pandemic. Thanks to the generous nature of people like Sergio Terrera (Chief of the Water Library and Historical Archive), Dra. Marcela Andino (Institutional Management Secretary), and Rubén Villodas (Director of Water Management of the Department).
Coupled with some of my own research, here's what I found out:
Trash in the Waterways - Changing a Culture of Littering and Dumping Trash is Key to Alleviating Many Drainage Problems
While many citizens of Mendoza have a working knowledge of the oasis and acequia system, many do not and may not think about or care how their actions of dumping trash in these waterways can affect flooding throughout the entire region, not to mention the negative environmental effects these actions have. It is clear that more public awareness is needed to help change this culture towards one of stewardship and personal responsibility.
Another challenge for the acequias is that they compete against themselves to act as both irrigation channels and drainages. As irrigation channels, they naturally need to move less volume as they extend downstream so they are constructed smaller and more narrow as you go down the hill. Conversely, drainages accumulate more volume as they move downstream and need to maintain or even increase their capacity. While they function well for irrigation, their drainage capacity is limited. As this heritage infrastructure is heavily enmeshed in the city's design and layout, it poses one of the greatest challenges for the consideration of modifying the drainage system.
Image above: Garbage collects in acequias and can cause avoidable flooding problems. Image credit: Diario El Sol Mendoza
Water Management - Compartmentalized Management Is Challenging For Coordination
Mendoza's water management is quite complicated and so to is its hydrology, topography, and infrastructure. While one can quite literally devote a career to trying to make sense of them all, and there are many excellent examples of these people in Mendoza, what is most important to understand about water management here and how it can be challenging is that there is no one organization that governs an entire watershed nor one that manages the water from the reservoir to its final destination. As it stands, there is the Department of Irrigation that is charged with delivering water from the reservoir to several key points throughout the region - usually at the periphery of a city. At each of these points, the water management then changes hands to a local entity, known as Channel Inspectors or caciques, organized by its respective municipality.
Functioning much like acequia communities in other areas of the world, these often democratic organizations decide how water is allotted, to who, and how much, as well as how maintenance will be performed. They are decentralized from the operation of the General Irrigation Department and have an elected leader or Channel Inspector, that is elected every 4 years by open elections among all the irrigators belonging to their area of jurisdiction. While having these disparate entities prevents complete political control over water in the region, it can also impede collective efforts to manage flood mitigation and other projects that require systemic planning and implementation.
Image above: Water Infrastructure network of Mendoza. Excerpt from appendix in "Hidrologia Mendocina" (Galileo, V.,1940)
Private Neighborhoods & Uncontrolled Development - Impervious Surfaces and Rapid Urban Expansion (Sprawl) are the Main Culprits
Perhaps the most influential element that we can see increasing the intensity of flooding is the all-too familiar theme of rapid urban expansion (urban sprawl), and it is no exception in Mendoza. In the last ten years, the city has experienced massive growth west of the city as private neighborhoods or privados have been developed seemingly overnight in the flood-prone drainages of the foothills (piedemonte). Hosting nearly 10,000 families now and as the development creeps further toward the mountains, so to does the expansive impermeable surfaces that are associated with these neighborhoods. Acting like the childhood game of king-of-the-hill, each impervious area created at a higher elevation creates increasing problems for their neighbors downstream. Many issues like this have become increasingly apparent and are beginning excellent discussions about inequality in planning for cities.
Image above: Basic geomorphology of Mendoza demonstrating the location of the Piedemonte region and why it is so critical to resolving flooding challenges. Image credit : Plan Municipal de Ordenamiento Territorial 2019, Ciudad de Mendoza.
In addition to the rapid growth, many of the developments have been created illegally, taking advantage of confusion about the protection of the piedemonte region. Because of this, many properties and lands have been purchased in highly prone flood zones. Recently, Mendoza ordered an official halt on all works in this area until an official and comprehensive flood assessment could be carried out. New legislation will now protect much of this region as open space in an effort to prevent further disturbance. Check out this article on how the city used this situation to craft several interacting laws to not only address the flooding problems, but also provide a more sustainable future.
Ley Provincial 4341/79: prohibits the development of subdivisions in alluvial zones.
Ley Provincial 4886/83: protects alluvial zones from impermeabilization.
Ley Provincial 6045: Preserves the area for the enjoyment of all citizens and the public use.
Image above: Urbanization built over flood plains and drainages. Image credit: Diario de Mendoza
Image above: Flood Risk map showing most intensity along drainages in the piedemonte. Image credit: Mendoza Post
Image above: Graphic demonstrating urbanization creep into the piedemonte drainages. Image credit: Mendoza Post
Image above: Aerial of western boundaries of the City of Mendoza. Legal and illegal settlements have continued to work their way up the fluvial channels of the foothills.
Image above: Aerial view of Dalvian neighborhood in Mendoza demonstrating a typical privado layout.
Mendoza is world-renowned for its traditions of integrating acequias and trees into the urban fabric to support a robust tree canopy (the basis of this current investigation); however, the private neighborhoods have not carried on this practice. In fact, they are nearly completely removed , physically and politically, from the infrastructure that supports the rest of the city. Additionally, many of these types of enclaves have strict tree and landscape ordinances limiting tree canopy size, which greatly reduces the type, amount, and abundance of trees that could otherwise provide many benefits to help reduce runoff. They also do little if anything to disuade the use of water-intenive plants, including lush turf lawns.
Image above: View of a private neighborhood in Mendoza. Large paved streets and lush, usually non-native, trees and plants are plentiful as is true with turf lawns. Image credit: Inmoclick.com
To address stormwater runoff, each property if fitted with a drywell (pozo), which is basically a hole or tank below the ground that allows water to infiltrate. These wells are intended to manage all of the runoff from each property and their size is based on the respective calculations. While these features are widely used to promote aquifer recharge and are seen as more sustainable practices in many places, it seems they are used in the neighborhoods as a necessity rather than a benevolent step towards sustainability (the neighborhoods are not connected to a municipal drainage/stormwater system) and must manage on-site in most cases).
Image above: Typical detail for residential drywell/pozo.
Destruction/Disruption of upland watershed and Sensitive Vegetated Surfaces
It goes without saying that the hasty, possibly illegal, and unsustainable development that has been creeping up the foothills has had an impact on the native fauna and land. In addition, other unregulated anthropogenic activities such as hiking, motocross, biking, and gathering firewood (leña) (many people depend on the sales of gathered firewood for their livelihood) have affected the native soils, vegetation patterns, and consequentially, the hydrology. As mentioned above, in response to this, the city is designating most of the upland areas adjacent to the city as protected open space in hopes to reduce some of the disturbance.
Image above: Typical piedemonte landscape typology. Even small disturbances can have big impacts when the land is this delicate. Image credit: Agua Book, 2.1.3., Gobierno Mendoza.
Image above: Areas highlighted in red to demonstrate the tendril-like development patterns that are working their way up the watersheds of the foothills (piedemonte).
Image above: Development is pushing up the the very limits of the mountains in some locations.
Aging and Under-Sized Infrastructure
Across the globe, cities are reporting one of their biggest challenges for the future is addressing failing infrastructure and maintenance demands. Now too, in light of climate changes and increased runoff from urbanized areas, many are experiencing issues with water infrastructure that is was never designed for such capacity. Such is true in the City of Mendoza. Many of the dams used to capture floodwaters are experiencing frequent problems with over capacity and is worsened by sediment and debris filing in behind the dams, reducing their holding capacity.
One of several dams keeping water from racing straight towards the city. Over time, sediment and other debris fill up against the dam lowering its holding capacity. Image credit: El Sol Mendoza
How Green Infrastructure and
Low-Impact-Development Can Help
Green Infrastructure (GI), Green Stormwater Infrastructure (GSI), and Low-Impact-Development (LID) are terms used to describe a new approach to designing our city infrastructures in response to the negative effects of massive highly-engineered concrete systems or gray infrastructure practices. They incorporate sustainability principles that seek to utilize natural processes and functions to benefit the built environment while maintaining or improving ecological and environmental conditions and seek to view water resources like stormwater as assets rather than liabilities (as is common with traditional engineering approaches or gray infrastructure). These practices can range from small-scale water harvesting practices at home like rain barrels/cisterns or rain gardens to large-scale interventions like infiltration basins or, in Mendoza's case, and entire city planned as an oasis. Though GI and LID interventions are important for managing stormwater runoff, it is most beneficial to combine both green and gray infrastructures to achieve effective and sustainable results.
Image above: Basic concept of green infrastructure versus a traditional approach.
The following are a few ideas that could be examined to help offset and manage some of the flooding in Mendoza and contribute to an overall more sustainable city and culture:
Higher Sustainable Design Standards for Private Neighborhoods
Many private neighborhoods and other similar developments tend to have a rubber-stamp approach, imposing their preconceived footprint on any terrain they see fit. Luckily there are new successful examples of neighborhood planning where the features of the landscape dictate the design and value of the neighborhood rather than the other way around. One example is High Desert Community in Albuquerque, New Mexico (USA) where the entire neighborhood is planned around the existing drainages, very similar to the context of Mendoza discussed above) and much of the native landscape was painstakingly protected and preserved during construction. Additionally, their ordinances require the use of native vegetation for private properties in the neighborhood and there are strong restrictions on anything can may distract from the native landscape theme. While this comes with a price tag, it is a good step forward in generating value around this kind of practice and can be implemented in various ways.
Images above: High Desert is a planned community in the foothills of Albuquerque, NM. designed to reduce impact on the sensitive foothill ecosystem and hydrology and integrate the architecture and infrastructure with the native landscape. Instead of creating engineered systems to manage water, the community is designed around existing arroyos and the natural features of the land. The results of this kind of design are measurable in a case study about the project - learn more here.
Facilitate Infiltration
Infiltration can be improved in numerous ways both on private property and regionally. Interventions such as bioswales or infiltration trenches can capture, convey, and infiltration stormwater runoff along roadways or parking surfaces. Other interventions like the drywell can be improved by enlarging their capacity or by creating a series of interventions that facilitate additional infiltration below ground.
Image above: Infiltration trench detail. Image credit: Bernalillo County LID Guidance Manual
Image above: Bioswales can take advantage of runoff for infiltration which can supplement some irrigation needs for planted vegetation. Image credit: Bernalillo County LID Guidance Manual
Image above: Dry wells can be designed to include other infiltration components or "treatment trains" that can provide more infiltration, further offsetting the runoff generated by impervious surfaces on the property. Image credit: American Geosciences
More Sustainable Neighborhood Ordinances
Allowing for larger trees, water harvesting, and promoting infiltration in neighborhoods, many of the harmful effects of impervious surfaces could be reduced. Additionally, as their is a lack of public education about the benefits and function of xeric or native plants, neighborhoods could provide resources to help owners understand how they might help offset their property's impact while making it look beautiful and more regionally appropriate through native plantings and xeriscape design.
Image above: Cistern can capture huge amounts of water that would otherwise runoff and contribute to flooding. While it may rain infrequently in Mendoza, this water can be stored and used for irrigation. Image credit: TFS Solar
Image above: Trees should be encouraged in the private neighborhoods for their ability to not only lower the temperatures through shade, but also for their ability to soak up runoff during large rain events, relieving flooding. Image credit: Arbor Day Foundation
Image right: Design guidance manuals for understanding xeriscape and native plants could be developed and made more easily accessible to residents of Mendoza. It may help encourage the practice and wider adoption of sustainable practices in private neighborhoods. Image credit: Albuquerque and Bernalillo County Water Utility Authority
Small-Scale Interventions in Upland Watershed to Reduce Runoff Intensity
Using small-scale interventions throughout the landscape of the piedemonte that can be constructed out of native materials with simple tools makes many of the following tools feasible for restoring some of the hydrologic function and vegetation.
Image above: Zuni Bowl - technique derived from native peoples in the southwestern United States, which uses the principles of hydrodynamics to help reduce water flows and remove suspended sediments in the runoff. Image credit: Wildlife Network
Image above: Check dams are excellent for reducing the velocity of flows in waterways. They are easy to build and reconstruct if damaged and the sediment that builds up behind them can help support vegetation growth. Image credit: Mother Earth News
Image above: Contour swales and other terracing methods can take advantage of slopes to slow down water and provide sufficient time for infiltration, which can also contribute to vegetation growth and erosion control. Image credit: Bernalillo County LID Guidance Manual
Systemic Green Infrastructure Planning
Small-scale interventions are great, but they don't count for much unless they function as part of a great whole. For that matter, it is critical to have a systemic approach to green infrastructure that functions as a complete city-wide or regional system and integrates both grey infrastructure (engineered concrete drainages) with green infrastructure. Much like the oasis of Mendoza, the system doesn't work without all of its parts operating cohesively. A popular term used recently - "Sponge City" seems to help portray the overall idea of this principle. Starting with the highest elevations in the watershed, various treatments or green infrastructure interventions can be planned and applied to work in unison or a "treatment train" given they are designed for their respective context and function. As water makes its way down hill, it can be slowed, infiltrated, stored, and spread out through various methods. Most importantly, every component is working together to improve environmental systems through reusing stormwater.
Image above: Sponge City concept. Image credit: Thrive
Image above: How GI looks at various scales Image credit: Tahvonen, O., 2018
Image above: Treatment Train concept. Image credit: Deep Root
So What?
It is safe to say that Mendoza could be considered more sustainable than most cities that tout themselves as such. Aside from the integrated green infrastructure system of the Oasis discussed in earlier posts, Mendoza has a remarkable amount of leaders that have helped to usher in many sustainable practices including recycling programs and other environmental education. Perhaps the focus on the flooding issues in the city may help usher in more systemic and intentional green infrastructure planning practices when considering new development approvals at the permitting stage, new requirements for developments and developers that require more sustainable practices, and perhaps these interdisciplinary practices may help naturally improve interjurisdictional and interdisciplinary communications when planning for the future of the city.
If you want to learn more, check out any of the included links above or send us a message!
