Long-term erosion control and channel stabilization for Arroyo de los Montoyas with PROPEX Armormax

Overview

The Arroyo de los Montoyas, a major drainage channel in Rio Rancho, New Mexico, experiences periodic flow after significant rain events, ultimately discharging into the Rio Grande River. The channel’s steep embankments were significantly affected by scour and erosion due to several major floods, threatening the adjacent Rio Rancho Wastewater Treatment Plant #6 (WWTP6). Any damage to WWTP6 could result in a substantial loss of sewer services, affecting up to 75% of the Rio Rancho community. Furthermore, WWTP6 discharges into a segment of the Rio Grande with designated uses that include irrigation, warmwater aquatic life support, livestock watering, wildlife habitat, and public water supply. 

To mitigate these risks, the Southern Sandoval County Arroyo Flood Control Authority (SSCAFCA) sought a long-term solution to stabilize the channel's slopes while preserving the integrity of the wastewater treatment plant and promoting groundwater recharge. SCCAFCA wanted a resilient flood control solution to provide protection up to the 100-year storm and allow ground water to recharge to infiltrate the soil instead of running onto concrete. Given the arroyo's limited right of way, highly erodible sandy soils, and severely deteriorated channel banks, the solution needed to deliver robust erosion control and channel stabilization in challenging conditions. After evaluating various approaches, SSCAFCA selected PROPEX^® Armormax^® as the most suitable erosion control system for the project. 

Challenge

The Arroyo de los Montoyas project presented a multifaceted challenge involving environmental, technical, and spatial considerations. With the arroyo’s proximity to WWTP6, ensuring the stability of the embankments was essential to prevent potential damage to the plant. Failure to protect this critical infrastructure could have disrupted 75% of Rio Rancho’s sewer service, compromising the city’s wastewater management. The environmental impact of untreated sewage discharge into the Rio Grande, which serves as an essential water resource for irrigation, aquatic habitats, livestock, and human consumption, further underscored the need for effective erosion control. 

Compounding these issues were the arroyo’s unique environmental and geological conditions. The embankments were subject to high rates of erosion and destabilization from stormwater flows, particularly following intense flood events. Due to the high sand content in the soil, the banks were highly vulnerable to erosion, resulting in slope instability that increased the likelihood of sedimentation and pollutants flowing into the Rio Grande.  

Moreover, SSCAFCA encountered spatial constraints due to the limited right of way along the left descending side of the arroyo. This restriction necessitated a stabilization method that could reinforce steep slopes without requiring substantial additional space for installation. Rock riprap and concrete was considered, but SSCAFCA did not want to a hard armoring solution based on research that hard armoring in arid arroyos limits groundwater recharge. Groundwater recharge is a critical component of the hydrological cycle, especially in arid regions, as it helps sustain local water tables. Hard armoring would prevent water infiltration, undermining SSCAFCA's goal of enhancing natural water flow and recharge within the arroyo.  

Solution

To address these challenges, SSCAFCA installed the PROPEX Armormax system, a high-performance erosion control and slope stabilization solution that combines high-performance turf reinforcement mat (HPTRM) with earth anchors engineered for optimal slope stability. PROPEX Armormax is proven to increase the factor of safety and significantly reduce the probability of slope failure. The system has been tested and approved by the U.S. Army Corps of Engineers (USACE) and is recognized by the Environmental Protection Agency (EPA), as a Best Management Practice (BMP) for water quality improvement.   

The PROPEX Armormax system works by creating a flexible, reinforced surface that stabilizes soil on steep or erosion-prone slopes. The HPTRM component provides a robust, reinforcement layer that is highly UV-stabilized, providing a design life of up to 75 years, even with direct sun exposure. This durability is critical for long-term protection of the arroyo’s embankments and adjacent infrastructure. Additionally, PROPEX Armormax’s permeable design promotes natural water infiltration, supporting SSCAFCA’s goals for groundwater recharge. By avoiding the runoff and impermeability issues associated with concrete solutions, PROPEX Armormax encourages stormwater to percolate into the underlying soil, recharging the groundwater and reducing downstream flood risks. 

System performance and environmental benefits 

The PROPEX Armormax system was specifically designed to enhance surficial stability in severe slope conditions, enabling SSCAFCA to stabilize the arroyo without extending into the limited right of way. By using PROPEX Armormax, SSCAFCA was able to apply a nature-based solution that mitigates erosion while also reducing sedimentation and pollution entering the Rio Grande. The installation of 29,800 square yards of PROPEX Armormax on both sides of the arroyo ensured a continuous barrier against erosion, enhancing the system’s resilience during flood events. 

One of the significant advantages of PROPEX Armormax is its role in sediment and pollutant reduction, a critical concern given the arroyo’s direct discharge into the Rio Grande. Through its HPTRM technology, PROPEX Armormax acts as a natural filter, trapping sediment and preventing contaminants from reaching the waterway. This benefit aligns with FEMA’s recognition of PROPEX Armormax as a nature-based solution for flood mitigation, contributing to the arroyo’s long-term environmental health and sustainability.  

The stabilization of the Arroyo de los Montoyas embankments exemplifies a balanced approach to erosion control, flood resilience, and environmental sustainability. By selecting PROPEX Armormax, SSCAFCA achieved its objectives for WWTP6 protection, groundwater recharge, and sediment reduction, fulfilling the project’s dual goals of infrastructure protection and ecological preservation. As arid regions like New Mexico face increasing challenges from extreme weather events and water scarcity, solutions like PROPEX Armormax provide a viable path forward in the responsible management of natural resources and community infrastructure. 

In October 2023, FEMA included this project in its Mitigation Action Portfolio (MAP), a collection of best practice mitigation projects. Additionally, FEMA recognized it as a nature-based solution.