DownloadA daily extract of the NPDES Conveyance dataset is available for download as a zipped file geodatabase.BackgroundAs a government agency that owns and maintains separate storm sewer systems, the Maryland State Highway Administration (SHA) is mandated to file a National Pollutant Discharge Elimination System (NPDES) permit with the Maryland Department of the Environment (MDE). The permit requires the inventory, inspection, and maintenance of SHA stormwater infrastructure. SHA is responsible for maintaining storm drain infrastructure on more than 5,000 miles of roadway statewide. SHA has developed a program consisting of SHA personnel, data managers, and subject matter experts to support the permit requirements and maintain these roadways. The tasks involved in the SHA NPDES data collection program are often completed by engineering consultants for SHA.The data are organized into a series of drainage systems with stormwater management facilities that are interconnected, allowing for flow-tracing function through distinct systems. A drainage system is defined as a series of storm drain structures or point features (i.e., manholes, inlets, endwalls) that connect hydraulically through conveyance features such as pipes and / or ditches. Closed and open storm drain structures are connected by pipe and ditch conveyance to create the drainage system. Stormwater management facilities (SWMF), also known as stormwater best management practices (BMP) are inventoried with the storm drain system. A system can include both open and closed storm drain features.ConveyanceConveyance features to be identified and inventoried include actual, physical features (pipes and ditches) and database connectivity features (hydraulic connectors). Conveyance is represented as line features in the database. Although they do not physically exist, hydraulic connectors should be inventoried to facilitate connection of drainage systems through stormwater BMPs; this is the only case where a hydraulic connector is created. Not every pipe or ditch conveyance is inventoried, but generally all conveyances between structures are inventoried. Conveyance features will have an upstream and downstream structure. When contract plans are not available showing proper conveyance for a storm drain system, conveyance can be determined by looking at the pipe(s) direction inside of structures. Field crews are not required to open manhole lids, and conveyance can be assumed at the field crew’s discretion when plans are not available.Pipes, Cross Culverts, & Driveway CulvertsPipes connect structures together in a system to maintain conveyance. Pipes consist of closed storm drain pipes, cross culverts, and driveway culverts. Rules for collecting cross culvert and driveway culvert pipes are described below. The following are rules that should be followed when collecting pipes within the storm drain network:All pipes between closed storm drain structures are inventoried.Pipes less than five feet in height are inventoried within SHA ROW.Pipes that are greater than five feet in height are not inventoried if they do not connect to closed storm drain structures. Pipes that are greater than five feet in height and do connect to closed storm drain structures are inventoried with the storm drain network.Closed storm drain systems that outfall through a pipe or culvert that is greater than five feet in height are inventoried. Pipe size, shape, invert, and material are recorded for all pipes. Because field crews are not required to open grates or manhole lids, this attribute information is most often gathered from contract plans. Pipe sizes and material should be verified in the field by observation through inlet grates and at end structures (headwalls, end sections, outfalls, projection pipes). Field crews should become familiar with different pipe sizes and materials prior to conducting field inventory.Cross Culverts are pipes, boxes, or arches that convey water from one side of the ROW to the other side, usually under the roadway. Cross culverts are inventoried as pipes. Depending on the situation and culvert size, not all cross culverts will be inventoried. The following are rules that should be followed when collecting cross culverts:The culvert height is determined from contract plans when available. Otherwise care should be taken to measure and estimate the actual culvert height in the field. This may require estimating the depth of sedimentation at the culvert ends to determine the feet of buried culvert.Culverts that are less than five feet in height are inventoried.Culverts that are greater than five feet in height are not inventoried.A culvert that is greater than five feet in height that has a closed storm drain tying in is not inventoried. Instead, the most downstream structure in the closed storm drain system is inventoried as a pipe connection at the location the storm drain system connects to the culvert.Driveway Culverts and entrance culverts are pipes, possibly with an end structure, that conveys water under driveways, utility access roads, or stormwater BMP access roads. Not all driveway culverts will be inventoried within SHA ROW. The following are rules that should be followed when collection driveway culverts:Private driveway culverts and culverts at farm or other access points that do not require access permits should not be inventoried. Culverts under entrance drives that provide two-way or greater traffic such as multi-family residential, commercial, public, or industrial properties are inventoried. Culverts under SHA-owned stormwater maintenance access or other utility access roads should also be inventoried.If the private driveway or access drive culvert has a closed storm drain structure such as an inlet or riser on the upstream or downstream end of the pipe, then the culvert should be inventoried.If a driveway culvert is excluded from the inventory, other adjoining closed drain structures completing the system should be connected using a ditch. The ditch in this case should be drawn through the culverts as if the culvert does not exist.DitchesDitches and open conveyance are channels or flow paths that connect open structures (headwalls, end sections, endwalls, projection pipes, inlets with open backs) in a system to maintain the conveyance. Attributes collected for ditches include material (vegetative, concrete, riprap, etc.), bottom width, and side slope. Not all ditches or open channels within SHA ROW are to be inventoried in the geodatabase. Ditches to be inventoried are the following:Ditches or open conveyance between open structures.Ditches or open conveyance greater than two feet in bottom width.Ditches or open conveyance that flow into stormwater BMPs regardless of bottom width.Hydraulic ConnectorsHydraulic Connectors connect the outfalls into stormwater BMPs to the control structure of the stormwater BMP to maintain conveyance through the system. Hydraulic connectors are used to represent connectivity through a stormwater BMP from inflows to control structures. Inflow points and control structures for stormwater BMPs should be connected with a hydraulic connector, including infiltration trenches. If hydraulic connectors do not exist in the previous inventory, the current development should create them. The hydraulic connector line features are stored in the CONVEYANCE feature class and no additional attribute information is collected. The connector is use so that connectivity between structures is maintained through stormwater BMPs and network tracing can occur.SimplificationsThe simplification process flattens database tables that normalize attribute information, resulting in a dataset with all attributes but also many null fields when the attribute type is not relevant to the SWMFAC type. The simplified data are a snapshot in time of the production NPDES data, updated every night.PublishingThis service was last published by Elliott Plack on 9/6/2019 based on a materialized view created by John Shiu. The service was republished on 11/26/2016 due to a security requirement on the source dataset.

DownloadA daily extract of the NPDES Structures dataset is available for download as a zipped file geodatabase.BackgroundAs a government agency that owns and maintains separate storm sewer systems, the Maryland State Highway Administration (SHA) is mandated to file a National Pollutant Discharge Elimination System (NPDES) permit with the Maryland Department of the Environment (MDE). The permit requires the inventory, inspection, and maintenance of SHA stormwater infrastructure. SHA is responsible for maintaining storm drain infrastructure on more than 5,000 miles of roadway statewide. SHA has developed a program consisting of SHA personnel, data managers, and subject matter experts to support the permit requirements and maintain these roadways. The tasks involved in the SHA NPDES data collection program are often completed by engineering consultants for SHA. The data are organized into a series of drainage systems with stormwater management facilities that are interconnected, allowing for flow-tracing function through distinct systems. A drainage system is defined as a series of storm drain structures or point features (i.e., manholes, inlets, endwalls) that connect hydraulically through conveyance features such as pipes and / or ditches. Closed and open storm drain structures are connected by pipe and ditch conveyance to create the drainage system. Stormwater management facilities (SWMF), also known as stormwater best management practices (BMP) are inventoried with the storm drain system. A system can include both open and closed storm drain features. StructuresPhysical stormwater structures to be identified and inventoried include headwalls, endwalls, cross culverts, pumping stations, stormwater risers and weirs, inlets, pipe connections, and manholes. Storm drain structures are represented as point features in the database. Several database features are included that are not existing physical structures, but are employed to facilitate connection of drainage systems in the database. For detailed descriptions of each feature, refer to the SHA Book of Standard for Highway & Incidental Structures, Category 3 “Drainage.” Storm drain structures within SHA ROW are inventoried. Information on private storm drain structures will need to be collected if a private system ties into SHA-owned storm drain features. The only structures that are not inventoried within SHA ROW are single residential driveway culvert end structures (See below for more details), bridge inlets, under drains, roof drainage, or other private tie-ins with the exception of the first or last structure from a private storm drain system and curb opening. If an under-drain pipe has an end structure (such as an endwall), then the structure is inventoried. Curb openings are only inventoried when affecting the drainage area for a BMP or major outfalls. If it is deemed necessary to include a curb cut in the database, the curb cut is captured as an inlet feature with comments identifying the feature as a curb opening. A curb opening is not a COG or COS inlet with an open back, but simply a cut in the curb where sheet flow is exiting impervious. The following are brief discussions of the structures in the data. See Chapter 2 of the Maryland SHA Stormwater NPDES Program SOP for more information, figures, and descriptions of each field. End / Head StructuresAn end / head structure is any structure at the upstream or downstream end of a culvert or pipe. These can include headwalls, endwalls, end sections, and projection pipes. Often the end / head structure is designated on the contract sheets and field verified. When contract plans are not available for a roadway, the SHA Book of Standard for Highway & Incidental Structures should be referenced if structure types are unfamiliar with field teams. Outfall areas are not to be inventoried, but will be analyzed during the inspection process. Headwalls (HW) are structures that are placed at the upstream end of pipes and culverts to provide a stable or hydraulically desirable entrance to the conveyance. Headwalls are usually concrete but can be constructed of wood or masonry, such as brick or concrete block. Wall structures on the upstream side of a culvert or pipe are inventoried as headwalls. Plan sheets may designate the upstream end of a pipe or culvert as an endwall, but these structures should be inventoried as headwalls. All wall-end structures at the upstream end of a pipe or culvert should be inventoried as headwalls. Endwalls (EW) are structures that are placed at the downstream end of pipes and culverts to provide a stable or hydraulically desirable exit to the conveyance. Endwalls are usually concrete, but can be constructed of wood or masonry such as brick or concrete block. All wall structures on the downstream side of a culvert or pipe are inventoried as endwalls. Plan sheets may designate the downstream end of pipe or culvert as a headwall, but these structures should be inventoried as endwalls. All wall-end structures at the downstream end of a pipe or culvert should be inventoried as endwalls. End Sections (ES) are structures that transition the ends of pipes into slopes and provide stability to the pipe entrances and outflows. End sections do not affect the hydraulic capacity or efficiency of the pipes. End sections can be constructed of concrete, metal, or plastic (HDPE). End sections can either be inventoried at the upstream or downstream end of a pipe. Projection Pipes (PP) are not physical structures but represent the upstream and downstream end of a pipe if an end structure on a pipe does not exist. Projection pipes are captured spatially as a feature and represent the ends of pipes. Inlet StructuresInlets are structures that collect storm drain runoff. Inlets convey the runoff to closed storm drain systems, open conveyance, or outfalls. There are many different types of inlet structures, and all are discussed in the SHA Standard Design Manual and should be reviewed prior to conducting an inventory. Spring heads are also inventoried as inlets. Inlets (IN) are hydraulic structure chambers below surface grade that collect storm drain runoff. An inlet either has a grate or open sides / curb to allow runoff to enter the storm drain system. Inlets are often constructed of concrete, masonry brick, or concrete block. Spring Heads (SH) are inventoried as inlets. Spring heads are inventoried only where they emerge and are connected to a storm drain system. Spring heads are inventoried because they provide evidence for the presence of ground water for dry weather flows during illicit discharge field screening operation. Spring heads may be identified from contract drawings or identified during the field inventory. Spring heads are mostly found in rural areas. Connection StructuresA connection structure is a storm drain structure that connects conveyance (pipes and ditches) within a system and is not an inlet, riser, weir, or pumping station. These can include manholes, ditch intersections, junction boxes, pipe connections, wye connections, capped inlets, pipe bends, and pipe directions. Because field crews are not required to open manhole lids and enter closed storm drain structures, no designation type is necessary for connection structures. All of the attribute data for these structures will be collected from contract drawings, including connection material and top of manhole elevations. The existence of connection structures should be field verified for spatial accuracy, even though the attributed data will be collected from contract drawings. For structures that are buried or paved over, a GPS point is to be recorded at the best estimated location in the field based on contract plan sheets. The verification of attribute table data for structures that cannot be verified in the field will be completed based on plan sheet information. This also holds true for structures that are buried or cannot be accessed; the attribute data should be obtained from plan sheets. Manholes (MH) are hydraulic structures that connect pipes through a system. They are used as access points to a system, to change direction or invert elevations for pipes, as a junction to change pipe size and / or material, and as a junction of multiple pipes to a single pipe. Manholes are frequently paved over or buried, but are still inventoried. Unless it is certain that the manhole does not exist, the manhole is inventoried. Manholes with lids that have designed holes to allow runoff to enter are inventoried as manholes and not inlets. Ditch Intersections (ID) are geographic representations of where ditches meet, begin, or end a system and are captured as point features. These features are used to define the extents of ditches. Junction Boxes (JB) are underground hydraulic structures that connect pipes through a system. They are used to change direction or invert elevations for pipes, to change pipe size and / or material, and to connect multiple pipes to a single pipe. Identifying junction boxes in the field is difficult because these structures are usually buried with no part of the structure exposed to the surface. Junction boxes are only inventoried from contract drawings and should never be assumed in the field, unless the field crew is certain the structure is a junction box. If the field crew suspects that pipes are merging together and no contract plans are available to confirm this, the connection should be inventoried as a pipe connection and not a junction box. Pipe Connections (PC) are locations throughout the conveyance of a system where two or more pipes connect. A pipe connection is also captured at the location where a closed storm drain pipe connects to a culvert or stream crossing. Wye Connections (YC) are hydraulic structures that join two pipes together within a system’s conveyance. Wye connections will be identified from contract drawings and should not be assumed in the field. Instead of assuming a wye