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This report outlines the development of a suite of computer codes collectively referred to as MnDrain. These codes, embedded in a standard spreadsheet program, provide a user-friendly environment in which the consequences of an edge drain design decision can be investigated. The purpose of an edge drain is to remove moisture from the granular base of the road system. The rate at which moisture is removed will depend on the geometry and materials used in the base and the soil type in the subgrade. MnDrain allows for evaluation of a given drain design against Federal Highway Administration requirements. In MnDrain, the user can chose from three basic scenarios, select material types and adjust geometries for each scenario, and calculate the moisture removal versus time curve over a two-hour drainage time. The work in this report shows that MnDrain is easy to use, flexible, and produces accurate approximate solutions of the Richard's model of variable saturated flow in a layered media. MnDrain also offers the advantage of offering free access to all source codes, which means that MnDrain can be reconfigured to deal with a large array of pavement drainage issues.

This paper summarizes current subsurface pavement drainage used by various state and local agencies. The paper starts with a brief introduction on moisture in a pavement and the damage it can cause. Following the introduction, the relative effectiveness of subsurface drainage is estimated based on environmental conditions, traffic levels, and physical characteristics of the pavement structure. The next three sections of the paper discuss various components used in subsurface drainage, combinations of drainage components to perform specific drainage tasks, and maintenance required to keep drainage components functioning. Next, results from a survey sent to Minnesota city and county agencies are given summarizing current drainage practices used on lower volume roads. Finally, the last part of the paper gives cost and performance data on drainage systems used by various states.

This study provides design information for temporary stormwater ponds with floating head skimmers. The purpose of the ponds is to remove suspended sediment and nutrient loads from stormwater runoff on active construction sites. The design information is directed at meeting the standards in the National Pollution Discharge Elimination System (NPDES) general permit which includes storing runoff from the 2-year, 24-hour rainfall event or providing the equivalent sediment control. The study results include: Research of currently available floating head skimmers, Estimation of runoff hydrology and hydraulics from active constructions sites using HydroCAD, Estimation of water quality improvements using P8, and Design plans. The study shows several available technologies for pond skimming. The pond and skimmer design manages a 2- year, 24-hour rainfall event while removing an average of 80 percent of total suspended solids (TSS) from runoff. Smaller systems do not operate equivalently without additional treatment such as adding flocculants. Plans, maintenance requirements, and special provisions are included.

Roadside swales are drainage ditches that also treat runoff to improve water quality, including infiltration of water to reduce pollutant load. In the infiltration study, a quick and simple device, the Modified Philip Dunne (MPD) infiltrometer, was utilized to measure an important infiltration parameter (saturated hydraulic conductivity, Ksat) at multiple locations in a number of swales. The study showed that the spatial variability in the swale infiltration rate was substantial, requiring 20 or more measurements along the highway to get a good estimate of the mean swale infiltration rate. This study also developed a ditch check filtration system that can be installed in swales to provide significant treatment of dissolved heavy metals and dissolved phosphorous in stormwater runoff. The results were utilized to develop design guidelines and recommendations, including sizing and treatment criteria for optimal performance of the full-scale design of these filters. Finally, the best available knowledge on swale maintenance was combined with information obtained from new surveys conducted to develop recommendations for swale maintenance schedules and effort. The recommendations aim toward optimizing the cost-effectiveness of roadside swales and thus provide useful information to managers and practitioners of roadways. The research results and information obtained from this study can thus be used to design swale systems for use along linear roadway projects that will receive pollution prevention credits for infiltration. This will enable the utilization of drainage ditches to their full pollution prevention potential, before building other more expensive stormwater treatment practices throughout Minnesota and the United States.

Culvert pipe material selection has traditionally been a relatively simple task involving metal or concrete pipe. In recent years, the addition of coated metal and plastic pipe has led the federal government to implement a rule requiring the consideration of alternative pipe materials. The current MnDOT Drainage Manual provides limited guidance on the selection of pipe material. The manual is lacking detailed information on the influence of environmental conditions on pipe durability in Minnesota. It is necessary to provide updated, accurate information on pipe material and durability for factors directly related to Minnesota. To reach this goal, the availability and suitability of existing data, as well as the practices associated with predicting pipe life spans must be evaluated. This report is the result of the initial feasibility study for a larger project(s) to update the MnDOT Drainage Manual. The goal for this report is to identify knowledge gaps, produce a research plan that will guide future research, and draw any pipe materials conclusions possible using the data available.

Roadside drainage ditches (roadside grassed swales) typically receive runoff directly from the road and water is infiltrated over the side slope of the ditch, similar to a filter strip. Water that runs off the side slopes then has a further opportunity to infiltrate as it flows down the center of the ditch. This research focuses on the volume reduction performance of grassed drainage ditches or swales by infiltration. A total of 32 tests were performed during three seasons in four different highways maintained by MnDOT in the Twin Cities metro area. The field-measured saturated hydraulic conductivities (Ksat) correspond to hydrologic soil group A, even though the soil textures indicated correspondence to hydrologic soils groups A, B and C. This means that the infiltration performance is better than expected for these types of soils. In addition, the trend was to have more infiltration when the saturated hydraulic conductivity was higher and for a greater side slope length, as expected. A coupled overland flow-infiltration model that accounts for shallow concentrated flow has been developed. The predicted infiltration loss has been compared with the actual infiltration loss determined from the monitored field tests. In this manner, the validity of the model as well as the associated soil hydraulic and surface geometry parameters have been evaluated. Using the coupled infiltration-overland flow model, multiple scenarios with sensitivity analyses have been computed, and the results have been used to generate a simplified calculator to estimate the annual infiltration performance of a grassed roadside drainage ditch.

This project involved the evaluation of some configurations of pavement subsurface drainage systems, including the conventional edgedrain system, and two centerline configurations, at 2-foot and 4-foot depths. Testing of these configurations took place on a newly constructed eight-mile section of Nobles County CSAH 35 near Worthington. Drained roadway sections were 500 feet long for each drainage treatment. Each of the treatments was replicated six times, with the outflow for each replication outlet through a tipping-bucket flow monitoring system. The experimental design tested both the drain configuration and the effect of relative elevation of the roadway. Measurement of relative wetness of the pavement base and subgrade materials for each of the drainage treatments was conducted with a Geonics electromagnetic induction instrument (EM38). Data were collected from March 2006 until November 2008, with breaks during the winter periods. Statistical analyses were conducted to look for treatment effects, using both drained volumes as well as the EM38 measurements as measures of drain efficacy. Additional project work included a finite element analysis of the drainage configurations, EM38 evaluation of drainage effectiveness of an open-graded base construction for streets in the city of Worthington, and evaluation of the potential drain plugging effect of crushed concrete fill.

A guide for evaluation of highway subsurface drainage needs and design of subsurface drainage systems for highways has been developed for application to Minnesota highways. The guide provides background information on the benefits of subsurface drainage, methods for evaluating the need for subsurface drainage at a given location, selection of the type of drainage system to use, design of the drainage system, guidelines on how to construct/install the subsurface drainage systems for roads, and guidance on the value of maintenance and how to maintain such drainage systems.

Vehicular traffic contributes a large fraction of the pollutant load in stormwater runoff from roadways. While runoff concentrations have historically been characterized for urban roads with high average daily traffic (ADT); the runoff quality from paved rural roads that have relatively low ADT is largely unknown. In this study; runoff from low-volume roads (ADT < 1500) in Minnesota was monitored at 10 locations during 174 rainfall events in 2018 and 2019. The initial concentrations of total suspended solids (TSS); total phosphorus (TP); nitrate+nitrite; and heavy metals in the runoff; and the relationship between measured concentrations and site-specific conditions were analyzed. Concentrations were strongly influenced by the surrounding land use and soil type. Sites with agricultural lands had higher mean TSS; TP; and zinc concentrations; and lower nitrite+nitrate concentrations than wooded sites; which can be related to the type of soil that would get transported onto the roadways. When compared to existing urban runoff quality data; the estimated event mean concentrations (EMCs) in rural road runoff were substantially lower for copper and zinc and marginally lower for TSS; TP and nitrate+nitrite. Based on detailed cost-benefit analysis of various roadside treatment options; roadside drainage ditches/swales are recommended for cost-effective treatment of runoff from low-volume roads over ponds; sand filters and infiltration basins. Example road widening projects were also modeled to determine how stormwater management requirements can be achieved using drainage ditches/swales.

Over the last thirty years, the Minnesota Department of Transportation (MnDOT) has implemented biofilters along roadways as a stormwater control measure. The state and national regulations require that the biofilters must be able to infiltrate and treat the first inch of rainfall onsite. However, the performance of the biofilters after installation has rarely been studied. An early phase of this project monitored two newly constructed biofilter sites for two years and for three months, respectively. This study extended the monitoring of soil moisture changes and infiltration water quality for another two years (2019-2020). Over the four-year monitoring period, both salvage peat and compost materials showed the capacity to retain the first inch of runoff, and this retention capacity did not change over the study period. The drainage water quality showed significantly temporal trends, particularly phosphorus concentrations, which were declining significantly for both compost and salvage peat. The application of tailing with compost can reduce the phosphorus release. The leachate from salvage peat has similar metal concentrations but much lower phosphorus concentrations (below 100 ppb) than the compost. The lowest chemical concentrations were achieved when the soil mixture contained 10% compost and 10% salvage peat, implying the best stormwater control practice is to limit the organic ratio to around 20%. Findings from this work determined the validity of using peat and compost for future biofilters and can aid in future design.