Water-Resources Investigations Report 92-4147, "Effectiveness of highway edgedrains," In Reply Refer To: December 2, 1992 Mail-Stop 415 OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM 93.05 Subject: Water-Resources Investigations Report 92-4147, "Effectiveness of highway edgedrains," by Hillary H. Jeffcoat, F. A. Kilpatrick, J. Brian Atkins, and J. L. Pearman The purpose of this memorandum is to announce and transmit the subject report, which was prepared in cooperation with the Federal Highway Administration. It details a study performed in 10 States to study the effectiveness of retrofitted edgedrains in removing surface and subgrade water from highways. The 10 highway sites were instrumented to measure concurrent rainfall and edgedrain discharges, piezometric water levels, and soil moisture under the pavement and adjacent shoulders. Soil samples were also collected and their physical and hydraulic properties measured; all sites were found to have relatively low permeabilities. Fifty selected rainfall-runoff events were analyzed to assess the amount of infiltration reaching the pavement subgrades, amounts and timing of edgedrain discharges, and the manner of water movement beneath the pavements. The data indicate that retrofitting longitudinal edgedrains to an existing highway provides a sink to collect water draining laterally off the pavement surface as well as water reaching them from the subgrade voids and channels. The tight, low permeability subgrade material found to exist at all 10 sites precluded ready lateral drainage with or without edgedrains. The data indicate that most of the lateral subgrade movement of water is through voids and channels that develop under the pavements. In addition to providing data as to the effectiveness of edgedrains, this study also developed and tested instrumentation and techniques for studying pavement drainage. A dual-tipping bucket gage proved most effective in concurrently measuring rainfall and edgedrain discharges. Pressure transducers were effective in measuring piezometric water levels beneath the pavements. Data loggers proved effective in not only recording all data but could be programmed to operate the sensors only to the extent needed. The need to acquire and analyze core samples of the subgrade material for physical and hydraulic properties in emphasized. Additional copies of this report may be obtained from: Hillary H. Jeffcoat or F. A. Kilpatrick JEFFCOAT (703) 648-5010 (205) 752-8104 Ernest F. Hubbard Assistant Chief Office of Surface Water Attachment WRD DISTRIBUTION: A, B, S, FO