Storm drains collect storm runoff from buildings, streets, parking lots, and unpaved areas and convey this water to a desired outfall. Access holes (or manholes), which allow staff to inspect, maintain, or repair a segment of the drainage, are usually spaced about 92 to 183 meters (m) (300 to 600 feet (ft)) apart along a given pipe, at every junction between multiple pipes and at changes in horizontal or vertical direction. An access hole, which has at least one inlet pipe and one outlet pipe intersecting it, is usually constructed from a vertically oriented concrete pipe or box that is large enough for a person to enter by removing the cast iron lid and using a ladder. In addition to allowing access, access hole junctions also allow pipes to easily change one or more variables: direction, slope, diameter, and elevation. Storm drain systems include Stormceptors in highly developed urbanized areas where land use is too restrictive for conventional/natural devices. A Stormceptor is a stormwater separator that removes sediment and hydrocarbons from urban runoff. Estimating the energy loss associated with these access hole junctions and stormceptors is a critical step in designing a drainage network that can handle the incoming flow from various storm events. In addition, addressing flooding by replacing existing storm drain system where right-of-way and access is confined can be difficult. If retrofitting existing access holes can significantly reduce headloss, construction can be limited to the access holes and reduce construction costs .In order to determine if it is feasible to significantly reduce head loss for existing polygon junction structures, there is an immediate need to develop more information about the flow characteristics in these junction structures. FHWA Hydraulics R&D just recently finished a new series of junction loss experiments in order to validate a new design methodology to estimate loss through circular junction structures. The study did not investigate rectangular/square access holes and did not address losses through stormceptors. Therefore, there is a need to research losses through rectangular/square access holes, to study losses trough stormceptors and to adjust the new FHWA junction loss design methodology to rectangular/square (polygon) access holes.

The objective of this project is to develop a report to document the study approach and the research results. The report will include a practical design method for estimating losses through rectangular/square (polygonal) access holes and losses related to various stormceptors structures. The proposed study is to investigate head losses through polygonal junction structures and stormceptors. The study will be conducted by the FHWA at the Turner-Fairbanks J. Sterling Jones Hydraulic Research Laboratory in McLean, Virginia. The new junction loss experiments will include relative access hole diameters of less than 4, flow depth, angles of 90 degrees and less between incoming and outgoing pipes, shaped inverts and lack of inverts, high velocity flow where the incoming and outgoing pipes are under pressure and various stormceptor structures .Advanced 3D/Stereo particle image velocimetry (PIV) technology will be used for measuring instantaneous flow fields in the outflow pipe. Particle image velocimetry technique (PIV) is an optical flow diagnostic based on the interaction of light refraction and scattering with inhomogeneous media. Standpipes will be attached to sides of the inflow and outflow model pipes. The water column in the standpipes will represent the Hydraulic Grade Line (HGL) in the in and outflow pipes. Contact Image Sensors (CIS) mounted on the side of the standpipes will scan the water columns and record the HGL. Several test runs/cases will be validated and supplemented using high performance computational fluid dynamic (CFD) modeling at Argonne National Laboratory. This tool will be utilized especially where physical modeling is limited and will allow performing flow simulations for prototype structures.

The scope of work consists of researching junction losses through rectangular/square (polygonal) access holes for various relative access hole diameters, various angles between in and outflow pipes, shaped inverts, high velocities under pressure and researching losses for various stormceptor structures. The project will consist of the following tasks: Task 1. Assemble a technical advisory committee that will provide oversight and guidance on all aspects of the project. Task 2. Solicit information from participating states/local agencies on current methods being used to estimate losses through polygonal access holes and stormceptors. Solicit information on the range of variables (access hole shapes, sizes, slopes, relative access hole diameter, various angles between in and outflow pipes, inflow conditions, outflow conditions, inverts, stormceptor structures and flow velocities), which need to be considered in their storm drain system designs. Task 3. Based on the input received from the participating states, develop a detailed study matrix for the hydraulic tests. Task 4. Fabricate transparent models of the polygonal access holes and stormceptors that will be studied on a scale of 1:6 for access holes and 1:10 for stormceptors. Conduct various hydraulic flow test runs; varying relative access hole diameters, angles between in and outflow pipes, invert conditions, in and out flow velocities and stormceptor diameters. The new experimental procedure developed by FHWA Hydraulics R&D to determine outflow loss and inflow for access holes utilizing 3D/Stereo PIV will be applied. Task 5. Perform high performance CFD modeling to simulate laboratory experiments and to extrapolate small scale measurements to large scale prototype access holes and stormceptors. Use high performance CFD modeling also to supplement physical modeling especially where experimental settings are limited and not feasible. Task 6. Analyze data and develop a design procedure to estimate losses through rectangular/square (polygonal) access holes and stormceptors structures. Modify the new FHWA (HEC-22) junction loss design procedure to include rectangular/square (polygonal) access holes and stormceptor structures. Task 7. Prepare a report to document the study approach and results. The report will include a practical design method for estimating losses through rectangular/square (polygonal) access holes and stormceptors structures and can be used to improve the performance of existing polygonal access holes and stormceptors structures.

Suggested contribution: $25,000/year The Federal Highway Administration will serve as the coordinator for this pooled-fund project. State DOTs and local agencies will be solicited for their interest and participation in this study. FHWA will issue a task order contract to the support services contractor to conduct the study. Periodic reviews will be arranged to keep participating states and agencies up-to-date on current developments. These reviews may include meetings in Washington D. C. during the annual TRB Session, e-mail submittals and conference calls.