Background

The city of Queretaro is the capital of the state of Queretaro, located in central Mexico. About 200 km northwest of Mexico City, Queretaro has an arid to semi-arid climate with an average yearly temperature around 70°F and a yearly precipitation of only 374.6 mm (Comision Nacional del Agua, n.d.). The city of Queretaro has a population of just over 1 million people, adding its metropolitan area brings the population to 1.5 million people, making it one of the fastest growing regions in Mexico (INGEI, 2020). In the 50 years between 1970-2020, the population of the Queretaro area has tripled from 500,000 to nearly 1.5 million (Kirkland, 2020). With this population growth has come rapid urbanization and increased demand on and extraction of groundwater from the Queretaro aquifer. 

Hydrology of the Region

The city of Querétaro is situated on a valley spanning 2,700 km2, which is part of the Lerma-Santiago watershed. This watershed is linked to Chapala Lake in the state of Jalisco, and the surface water flow within the region is relatively limited (Castellazzi et al., 2021).

The primary surface runoff in the area is the Querétaro river, which only carries water during the rainy season. This water is stored in a series of dams and small reservoirs (Carrera-Hernández et al., 2016). Querétaro sits on two aquifers: the Valle de Queretaro, which spans the municipalities of Queretaro, Corregidora, and El Marqués, which has an area of 563 km2, a franchised water volume of 129.41 Mm3/yr, and a recharge deficit of 63.72 Mm3/yr. Currently, this aquifer is overexploited. The Valle de Buenavista aquifer, which covers an area of 319 km2 and is primarily located in the municipality of Querétaro, has a franchised volume of 22.61 Mm3/yr and presents a deficit of 12.44 Mm3/yr (Municipio de Querétaro, 2022). It is essential to note that the limits of these aquifers are determined administratively, rather than physically, and their actual boundaries are shared with municipalities in the state of Guanajuato (Carrera-Hernández et al., 2016).

Prior to the operation of the new aqueduct in 2011, Querétaro city heavily relied on groundwater, resulting in an annual decline of 2.5 meters in the water table, and a total drop of 100 meters between 1971 and 2010. In the following years, the extraction rate of public wells was reduced by 40%, leading to a recovery of recharge. However, this recharge is considered temporary as extraction rates continue to exceed groundwater recovery (Carrera-Hernández et al., 2016).

The valley where Querétaro city is located is at the intersection of three geological provinces: Mesa Central, Trans Mexican Volcanic Belt, and Sierra Madre Oriental. The Taxco-San Miguel de Allende and Chapala-Tula fault systems intersect in the area, resulting in a grid of faults with rectangular blocks that have normal differential displacements (Carrera-Hernández et al., 2016). Due to the hydrological setting and overexploitation of groundwater, uneven land subsidence and ground fracturing have occurred. However, after the operation of Acueducto II, ground deformation reduced from 25 to 50 mm/yr to around 10 mm/yr (Castellazzi et al., 2021).

Urbanization with land use change, loss of forests, and agricultural land has led to a reduction in groundwater infiltration and altered hydrological runoff processes.

Water Portfolio

Querétaro heavily relies on two sources for its water supply: groundwater extracted through drilled wells and surface water from the Moctezuma river, which belongs to the Pánuco hydrological region and is located at the state’s border with Hidalgo. Water from the river is transported through the Aqueduct II, an aqueduct approximately 123 km long. According to the Public Registry of Water Rights (REPDA) from the National Water Commission (CONAGUA), there are 313 active wells in the city (Castellazzi et al., 2021).

Treatment Plants

The city has one potable water treatment plant, which is part of the Acueducto II infrastructure, located in the municipality of Cadereyta de Montes. Its installed capacity is 1500 l/s. In 2021, the city had 63 wastewater treatment plants with a combined treatment capacity of 997.1 l/s (Municipio de Querétaro, 2022).

Stormwater Canals
The State Water Commission (CEA) is responsible for operating the stormwater infrastructure, which is integrated by drainage collectors, open stormwater channels, and reservoirs. The combined length of the system is 84 km with 12 reservoirs (Recolección Pluvial, n.d.).

Challenges

In our research, all the problems mentioned in articles, websites, government documents, news articles, and NGOs were listed and categorized into 5 groups. Although each problem has some relation to all groups, we placed them within the group we considered most relevant. Those groups are: Environment with challenges that highly involve the physical context of the city, Population with issues related to people living within the boundaries of the city and their problems with water access, Urban with major problems that concern the city as a whole, Infrastructure with challenges related to the Water State Commission (CEA) and its operation, and Government with issues related to law and planning.

Zeroing in on Subsidence

The city of Querétaro faces many interconnected problems to achieving a sustainable water future. In examining these challenges, subsidence was a clear and concrete problem that is having and will continue to have a significant impact on the city. Subsidence is related to a broad range of these issues, including the current deficit of annual water availability in the Querétaro aquifer, the threat of urban sprawl to natural areas serving as recharge zones, and the insufficient water sources in the city, which will ultimately pose huge risks to water infrastructure and the city as a whole.

Adopting a Three-Pronged Approach for Subsidence

We designed a three-pronged approach to address subsidence, focusing on protecting recharge zones, reclaiming and reusing wastewater and stormwater. To have a profound impact on an issue like subsidence a multifaceted approach was needed to present a holistic solution addressing the different factors which affect this problem. With a small water portfolio for sources of water only consisting of the Aqueduct and the aquifer, this approach allows for the reclamation and reuse of wastewater and stormwater as an alternative water source and the recharge of the city’s aquifer through the protection of recharge zones.

1. Protect Recharge Zones

Rapid population growth and urbanization in the city are currently threatening vital recharges zones for the Queretaro aquifer. Many of these recharge areas represent some of the last remaining natural areas and green space in the city. It is necessary to protect these recharge zones from development and prevent land use change to more urban/industrial spaces to allow for sufficient aquifer recharge. The city experiences many limitations and barriers for environmental governance policy of urban land planning. There is a large breakdown in both horizontal and vertical integration of policies, stakeholders, and sectors involved in land use planning. Many of these have competing interests or contradict one another, preventing a unified plan for sustainable urban development and environmental management as the city continues to grow and sprawl.

For example, at the federal level there are agencies and policy regulations in place to prevent urban sprawl and protect natural spaces in growing metropolitan zones. However, there are no mechanisms or guidelines to link procedures and stakeholders from federal to state to municipal levels and there is little to no enforcement of such regulations at the municipal level. There is also a lack of horizontal integration to link policy frameworks across different sectors of land zoning, urban development, and environmental protection. This lack of horizontal integration at the municipal level is evident through the mere requirement to recognize the Local Land Use Zoning Programs (POELs) but not need to comply with them (Soria et al., 2020). A both vertically and horizontally integrated approach to policies, stakeholders, and sectors involved in land use planning is needed to unify goals and plans to ensure the protect of recharge zones in the city of Querétaro.

Land use change is approved despite the validity of the Regional Environmental Land Use Zoning Program (POER), which began in 2009. A study depicted in the map above found that from 2009-2017, 67% of land use changes were approved in protected lands of high ecological value, and 40% of these land use changes were in areas crucial to recharge of the aquifer (Soria et al., 2020). We suggest that mandating compliance with the POER (state level) POELs (municipal level) to ensure sustainable environmental planning and management, urban development, and zoning in the city. More stakeholders like the public and environmental experts also need to be consulted in the land use change permission process, because as of right now this is a process process between private industry and local government official allowing the private sector to manipulate the little regulatory framework that exists for sustainable development (Soria et al., 2020).

Protecting recharge zones from development and preventing land use change will prevent future subsidence and allow for groundwater to replenish through percolation. However, protection of this land will also allow for the preserving of natural areas in the city. This provides countless other environmental social co-benefits through access to green spaces, protection of habitat, resources, and biodiversity, and the creation of a cleaner and more climate resilient environment.

2. Reclaim/Reuse Wastewater

The second part of our intervention for subsidence in Querétaro deals with wastewater treatment reclamation and reuse in the city. The map above depicts the most severe subsidence areas in close proximity to the city’s largest wastewater treatment plants, both public and private. These subsidence zones are located to the left of a large fault that bisects the city and in a largely industrial area. It is likely that many of these industries are water intensive and are drawing well water from the aquifer below, although we could not corroborate this. To combat subsidence in this area, we propose a wastewater reclamation and reuse system at these wastewater treatment plants. This would allow for the reclamation and treatment of wastewater to a level where it could be reused in industrial and agricultural processes. This should be combined with policies and/or concessions on pricing to incentivize industry and agriculture to use this reclaimed wastewater. The treated wastewater then serves as an alternative water source to the aqueduct and groundwater pumping and creates a use for treated yet nonpotable water instead of being put back into local waterways. Policies should also be implemented to require industry to treat their wastewater on site for reuse. This is beneficial both to prevent the need for potable water to be used in industrial processes, but also takes the burden of cost of treatment off the public utility and puts it on industry. An option for the future would be to explore injection of this reclaimed wastewater into the aquifer to assist with replenishment, especially given the areas of greatest subsidence are near the city’s wastewater treatment plants which could result in great damage to infrastructure.

This solution not only helps prevent future subsidence and replenishes the aquifer, but it also grows the limited water source portfolio by using treated wastewater as an alternative water source and allows for different levels of treatment for different water uses. This intervention also impacts the current water source portfolio by limiting the need for further withdrawals from the aquifer and reduces the need to transport more water via the aqueduct or construct another aqueduct.

3. Reclaim/Reuse Stormwater

The third approach deals with stormwater and proposes an infrastructure alternative by exploring green stormwater infrastructure (GSI) options. The drainage of rainwater in the city has been managed using an engineering-based approach, which means that natural drains in the city have been gradually covered with stone or concrete. The surface offers little friction and allows water to drain fast with the disadvantage of losing permeability and natural cover. The state government has been planning a master plan of channels to be implemented over the next decade. As mentioned before, urbanization is a major driver of the reduction of groundwater infiltration and land subsidence.

Figure 10 shows the current state of stormwater channels and new water wells drilled after 2011, the year when the Acueducto II started operations, and when a new restriction was imposed for drilling wells and extracting groundwater. We can see that many wells, both public and private, have been drilled.

We propose transforming part of the rainwater channels into swales, an GSI alternative that emulates the natural condition of the drain, allowing groundwater to recharge and introducing much-needed vegetation. Swale locations were chosen if they had a retention pond along the way, which would also be transformed into stormwater retention ponds, storing water, slowing the flow, and allowing infiltration.

The ecological restoration of the main river in the city is also part of the approach, as most drainage channels discharge into it.

Over the last few decades, the city has transformed into a major industrial pole of the country. Industrial parks with warehouses offer an opportunity to harvest rainwater from their large plastic or metallic roofs. Water collected can be either stored or sent to the proposed swales, which could improve water use in industries and allow for water infiltration.

Finally, we would like to mention that the implementation of these approaches could potentially be financed through special taxes, such as betterment levies imposed on new developments, and an increase in annual property taxes. Additionally, the inscription of natural and preserved areas to the carbon credit market could also provide a potential source of funding.

Conclusion

Querétaro faces a vast array of challenges that will impact the future of water in the city. While no single solution will fix every problem, our three-pronged approach for subsidence will have a critical impact on the city’s infrastructure, groundwater supplies, and alternative sources of water in the water portfolio. For future steps to address the issue of subsidence we suggest exploring how to lower demand by making consumption and usage of water more efficient and looking at infrastructure needed to provide industry and agriculture with recycled water. Alone this will not solve Querétaro’s water crisis as our approach does not address issues relating to alternative sources of potable water, inequitable access to water, and poor management of existing infrastructure, among other things. There are many opportunities to expand on this work for a large-scale water management plan for Queréraro encompassing its many interwoven challenges.

Works Cited