The Long-Term Performance, Maintenance, and Operation of LID BMPs in a Semi-Arid Environment
The long-term performance and feasibility of Low Impact Development Best Management Practices (LID BMPs) in semi-arid environments, like southern California, has not been well-verified in field settings. This knowledge gap spurred the Riverside County Flood Control and Water Conservation District (District) to construct an onsite LID Testing and Demonstration Facility to answer the following questions: What design lessons were learned during construction? How much runoff volume is reduced? What is the pollutant removal effectiveness? What type of maintenance is required? How can improvements be made to the designs?
The project scope included conversion of existing asphalt to permeable pavement, construction of planter boxes and a bioretention basin, replacement of turf with drought tolerant landscaping, and construction of a complete monitoring system. This facility is one of few projects that proactively incorporated monitoring of real-world LID BMPs. It was designed from the ground up to facilitate accurate data collection regarding pollutant management and hydrologic performance in order to protect California waterways.
During storms, data for pollutant concentration (including metals, nutrients, and bacteria), hydrology, and other water quality parameters are collected. Since 2012, data from 10 storms has been gathered. Trends over time have been studied in order to learn about the water treatment effectiveness of the LID BMPs. Results have shown that the LID BMPs perform relatively consistently in regards to volume reduction but pollutant performance varies. Specifically, data analysis has shown that the designs were weakest in nutrient and bacteria removal.
In addition to water quality data, maintenance strategies have also been analyzed. Over the past 6 years, the District has implemented typical LID BMP maintenance procedures and evaluated the results. Some operations and maintenance issues that were observed over the last six years were: pavement clogging, rodent damage, plant death, and flow path disturbance. The extent of these problems were also assessed by tests such as coring pavement and measuring infiltration. Multiple maintenance strategies were tested to compare results. Among our findings: rodent removal is crucial to a functioning bioretention basin and that when tributary areas are well-defined, localized pavement clogging does not significantly affect performance. Our findings are being used to gauge the feasibility of various long-term LID BMPs when taking into account maintenance costs.
Based on the collected data, current research, and lessons learned, the District has rehabilitated the facility. The “natural” LID BMPs (planter box and bioretention basin) have the highest potential for nutrient and bacteria reduction. With this in mind, design modifications were implemented. The planter box was retrofitted to create a saturated zone which many studies have reported to aide in nutrient removal. Plants and media in the bioretention basin were replaced to aid in overall pollutant removal. Experimental materials such as biochar and coconut pith were installed. The basin was also reconfigured in order to address issues such as rodent infestation and short circuiting. Other changes include updating monitoring equipment and protocol and maintenance procedures. The District has been monitoring these changes to evaluate the adjustments over time.
This multimedia presentation will discuss the lessons learned during various stages of the LID facility regarding construction, design, operation, and maintenance. With this knowledge, the District intends to improve its LID BMP Design Handbook which provides guidance to other agencies and developers. Ultimately, the field-tested designs would benefit the Santa Ana watershed as well as all of Southern California and its effort to implement sustainable practices for stormwater treatment.