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A comprehensive study and development of measuring instruments and techniques for measuring all components of flow in a storm-sewer drainage system was undertaken by the U.S. Geological Survey under the sponsorship of the Federal Highway Administration. The study involved laboratory and field calibration and testing of measuring flumes, pipe insert meters, weirs, electromagnetic velocity meters as well as the development and calibration of pneumatic-bubbler pressure transducer head measuring systems. Tracer-dilution and acoustic flowmeter measurements were used in field verification tests. A single micrologger was used to record data from all the above instruments as well as from a tipping-bucket rain gage and also to activate on command the electromagnetic velocity meter and tracer-dilution systems. INTRODUCTION In recent years with advances in watershed rainfall-runoff modeling techniques, there has been emphasis on the modeling approach to storm-sewer design. A reveiw of this type of literature is replete with statements as to the need for more and better data bases to aid model development. 1 » 2 > 3 The study performed in 1969 by the American Society of Civil Engineers (ASCE) recommended a minimum program of urban drainage research at $10 million over several years which amounted to about 0.33 percent of the expected annual national investment in the construction of storm drainage. A major conclusion of a conference on urban hydrologic research conducted in 1965 by the Urban Hydrology Research Council of ASCE was that a major technological hiatus exists largely because of an absence of suitable measuring devices. Progress has been made in these ensuing years in developing devices and methods of measuring and recording data in storm-drainage systems, largely in instrumentation. It is little wonder, though, that the problem still exists, as the hydraulics of flow in stormsewer systems may be extremely complex. STORM-DRAINAGE HYDRAULICS From the inception of rainfall, flow in roadways and gutters, collection via curb inlets and drop structures or catchments, and final conveyance from the area via lateral and trunkline pipes, the whole gamut of flow hydraulics can occur. 1 Flows in streets and gutters may be sheet flow (supercritical) depending on roughness and slopes; hydraulic jumps may form at transitions in grade or at inlets. Varying amounts of street runoff may bypass one inlet only to be collected at an adjoining one or by a series of downstream inlets. The efficiency of flows into curb and street inlets is highly variable and largely a function of approach and entry slopes, effective opening areas where grates exist, and the capacity of the receiving catchments and associated outlet drainpipes. In most cases, especially on major highway systems, the catchment outlet pipes are over-designed compared with the hydraulic capacity and efficiency of the curb inlets; this is to ensure passage of debris and to facilitate maintenance. Catchments may be simple or complex. A simple one receives the flow through a single curb inlet and discharges it through a single outlet pipe. A complex catchment is one receiving flow from several curb inlets and (or) from other pipes junctioning and flowing through the catchment: a combined catchment and junction box. The flow from the catchment through the outlet pipe may be quite complex depending on pipe area, roughness, and slope. Figure 1 depicts the possible SUBCRITICAL -DEPTHS AND-* FLOWS SUBCRITICAL AND "TRANSITION FLOWS" -DEPTHS AT OR GREATER THAN CRITICAL

Development and testing of highway storm-sewer flow measurement and recording system