As the demand for clean, fresh water in urban, agricultural, and other settings rapidly increases, counter-pressures in the form of drought, degraded water quality, inadequate infrastructure and an increasing reliance on imported water are multiplying. Combined with the effects of population growth, economic development, and impacts of changing weather patterns, cities also face increasing challenges with managing urban runoff to control nutrient loads and pollution of existing water sources. This apparent contradiction of not enough water for urban supply vs environmental degradation due to excessive runoff has spurred resource managers to develop a new perspective on stormwater management.
In order to establish an acceptable level of resilience in water supplies for both human and natural needs, a broad scale, integrated approach to the management of water resources is needed. This approach must encompass the management of all possible water streams, including potable, wastewater, and stormwater. Done correctly, an integrated approach should give cities the room to plan for the future and adapt to changing pressures of population growth, increasing urbanization, and the evolving effects of temperature and weather cycle changes.
Increasing Demands, Climate Change and Water Scarcity
As cycles of extreme drought and catastrophic flooding across the US have become all too familiar, crises related to aquifer depletion, groundwater contamination, and the demands placed on our nation’s largest rivers are coming into ever clearer focus. As cities face more and more water shortages, leaders have begun to evolve their view of stormwater runoff from a troublesome liability into a valuable resource.
The need to recognize and treat stormwater as a resource is increasingly urgent as more and more restrictions are placed on extracting water from conventional sources like rivers and aquifers. However, to realize the potential of stormwater as a usable resource, it will ultimately be necessary to change some fundamental principles of stormwater management. In traditional systems, for example, stormwater is ushered as quickly as possible out of developed areas and dumped into the nearest river, making it a highly polluted and destructive force which poses real threats to property, public safety, and public health.
Fortunately, many of the most important and impactful changes to stormwater management practices fold easily into an overall approach that embraces concepts like environmental sensitivity, sustainable growth, and low impact design. The underlying principle in all these philosophical approaches is finding a way for human use and development to work in concert with, instead of in opposition to, existing cycles and processes of the natural world.
As the effects of climate shifts continue to develop, whether it ultimately increases or decreases over historic levels, precipitation is expected to arrive in more intense events. As more stormwater falls in shorter periods of time, effects such as runoff, turbidity, and sedimentation inevitably increase. These effects degrade water quality and make stormwater management more difficult as a whole and their impact on surface waters in turn make the challenge of meeting potable water standards extremely difficult.
The reality is that more intense stormwater events are already here, and catastrophic events are becoming the norm. It’s inevitable that rising stormwater flows and their implications for flood management will have to be addressed. On the bright side, these realities bring communities new opportunities to create and expand stormwater harvesting and other Best Management Practices (BMPs) within the existing infrastructure.
Nontraditional Water Supplies (NTWS)
Nontraditional water supplies include reclaimed wastewater, desalinated seawater or brackish groundwater, along with various types of harvested rainwater and stormwater. Until recently, these were all typically considered fringe sources, suitable primarily for off-grid homesteaders or remote desert installations. In today’s world, however, traditional sources of potable water are becoming steadily depleted, contaminated, or simply inaccessible. This presents water utilities and municipal governments with an obligation to consider alternative sources to meet their constituents’ demands, not only for drinking water but for all the other uses of water within their communities.
Very much like fund managers, as the climate changes and populations shift (not always in a helpful direction), water utilities will need to diversify their investment portfolios (water supplies) to provide long-term reliability, resilience, and sustainability. This is likely to include “alternative” water sources such as harvested stormwater and graywater. In some instances, a shift toward relying on these kinds of nontraditional supplies is viewed as a substitute for investment in more traditional long-term water supplies and associated infrastructure. However, the benefits offered by these sources need to be weighed against corresponding trade-offs related to public health, the environment, existing infrastructure, and communities.
The Expanding Role of Stormwater Harvesting
As scenarios continue to change and evolve, planners will have to internalize the fundamental truth that all decisions have trade-offs. In this case, every resource that provides a benefit will inevitably have some challenges and risks associated with it. The biggest challenge in visualizing, planning, and implementing an overarching model for sustainability is balancing long term needs and risks for both the community and the ecosystem.
One of the pressing problems associated with stormwater management, water quality, and the vulnerability of potable water resources is that most current stormwater infrastructure (including many new green installations) is designed for frequent, relatively mild storms. The new normal of random, very powerful storms quickly overwhelms those existing facilities and raises concerns about contamination of local water supplies from flooding. In order to accomplish parallel goals of expanding available water sources, minimizing environmental degradation, eliminating the risk of disastrous floods, and doing so in a sustainable fashion, communities will need to envision a completely new approach to holistic urban design. Some stages of the process will inevitably be uncomfortable, even painful, but the benefits at the end should include fresher air, cleaner water, more comfortable urban spaces, and greater environmental security.
Both stormwater and graywater are valuable resources in the drive to support increasingly thirsty populations and industries across the globe. Even better, when these resources are systematically and responsibly captured and reused, they can provide drought resilience in vulnerable communities, as well as protecting and improving the quality of local surface waters.
In parts of the western United States, water has become so scarce that farmers are unable to support crops, and some communities have been forced to truck in water for the most basic needs, like drinking and cooking. Changing global weather patterns have triggered a series of record-breaking droughts in California and the Colorado River Basin, which have drained some of the country’s largest reservoirs and reduced river flow to levels never seen before. Meanwhile, populations are booming in some of the country’s most water-stressed regions, including California, Nevada, Arizona, Texas, and Florida, putting enormous pressure on existing resources.
When the demand for water has outstripped available sources, the conventional response has been to tap into underground aquifers or divert flow from rivers, perhaps assuming that those resources were essentially infinite. The result, today, is depletion and destruction of enormously important aquifers. The Ogallala Aquifer is the largest aquifer in the United States and stretches across 8 states, from Texas northward, across the High Plains to South Dakota. In some areas, the groundwater level has dropped 150 feet. In California, and elsewhere, depleted aquifers have begun to collapse, triggering an effect called subsidence, where the ground level falls with the loss of support the aquifers had provided. In the San Joaquin Valley, ground levels have dropped as much as 28 feet.
Vanishing groundwater and collapsing aquifers are scary examples of what happens when typical water sources are abused and overused, and those problems are not reversible - a collapsed aquifer cannot be pumped up again; it’s lost forever. Left unassisted, the Ogallala aquifer will likely take thousands of years to refill.
As businesses and communities have become more aware of water-supply pressures and the effects of overuse, some have already started to harvest stormwater and divert graywater for non-potable needs like irrigation and toilet flushing. Neighborhoods may use captured stormwater to keep nearby parks green and healthy, while remote rural areas may build a series of fire ponds to provide accessible water where hydrants are unavailable. On larger scales, some regions may capture stormwater specifically for groundwater recharge.
Stormwater capture not only increases the water supply, but it reduces damage to local surface waters and their ecosystems by reducing pollution that’s typically carried in with uncontrolled, unfiltered stormwater release. Reusing stormwater at the point where it’s harvested reduces the load placed on wastewater treatment plants, which can easily be overwhelmed during a severe storm event.
Still, even with a clear understanding of the advantages of stormwater harvesting and the support of community leaders, many utilities hesitate to embrace these new practices. For example, the threat of public health effects from water contaminated by chemical toxins or harmful microorganisms is an alarming prospect, especially without access to thorough research or an established regulatory framework to ensure public health protection without burdensome red tape and expense.
Stormwater harvesting and reuse is a critical step in the movement toward sustainable growth, water resiliency, and the protection of critical ecosystems. Fortunately, these practices are beginning to be incorporated into law at federal, state and local levels, but not quickly enough. As the need to embrace these practices is recognized, technology is inevitably advancing to meet the need. Still, legislative supports and structures must also move rapidly if the necessary changes are to be made.
