Subsurface Drainage:Subsurface Drainage
The Superlink (Ji, 1998) model has been included in GSSHA to simulate subsurface drainage networks. The Superlink model can be used to simulate urban subsurface drainage systems and agricultural tile drains. Systems can have both tile drains and surface inlets. Features include multiple networks, looped networks, discharge back on the overland and to channels. Superlink is implemented in GSSHA versions 5.1 and higher, and supported by WMS versions 8.3 and higher. The Superlink method and its implementation is described in detail in the following document: SUPERLINK TN.
To use Superlink include the STORM_SEWER card with the name of the Superlink pipe network file. The Superlink pipe network file, .spn file, describes the Superlink network, including the network, the connectivity of the network, physical attributes of drains, pipes, etc. The format of this file is very similar the channel input file, .cif file, used to described the stream network. When simulating tile drain, the connectivity between the tile network and the groundwater modeling grid is specified with the GRID_PIPE card, which is used to define the grid pipe file, .gpi file. This file format is very similar to the grid stream file, .gst file, used to describe the stream network connectivity to the overland flow grid. A Superlink network consists of a two level description of the network. The network and its connectivity are described with junctions and superlinks. Junctions can discharge to streams or to the overland flow plane. A superlink can contain individual pipes connected with nodes. These inter-superlink attributes can be used to describe changes in the pipe properties, or just to add nodes for computational purposes. Superlink is sensitive to node spacing, so it is important to space nodes properly. As an option, the user can let GSSHA assigned the individual nodes for computational purposes, using the SUPERLINK_C_OPT card. Inlet drains can be placed at both junctions and nodes. Inlets can be allowed to discharge back to the overland flow plane during pipe surcharge periods by using the HIGH_HEAD_RELEASE card in the project file.
Pipes in the Superlink network are made tiles by defining the hydraulic conductivity of the pipe as anything greater than zero. Flow into the drains is as described by Cooke et al., (2001). Flow into the tile follows the methods used in DRAINMOD (Skaggs, 1980) when using the SUPERLINK_DRAINMOD card in the project file. Tile drains only impact the system when used with the WATER_TABLE card, as described in Groundwater:Lateral_Groundwater_Flow_Modeling_in_the_Saturated_Zone. Typically, tile drains are used during simulations of the free water surface, GW_SIMULATION, as described in Groundwater:Lateral_Groundwater_Flow_Modeling_in_the_Saturated_Zone.
The inputs required to run GSSHA using the Superlink model are described in the following document: SUBSURFACE DRAINAGE REPORT. This report has not yet been approved for release. When approved for release this link will be made active. In the mean time, the inputs required to build a Superlink-based GSSHA model can be specified using the WMS interface.
- Cooke, R. A., Badiger, S., Garcia, A.M. 2001. Drainage equations for random and irregular systems, Agr. Water Manage. 48, 207-224.
- Skaggs, R.W. 1980. DRAINMOD Reference Report - Methods for design and evaluation of drainage-water management systems for soils with high water tables. USDA SCS, South National Technical Center, Texas.
- Ji, Z., 1998. General hydrodynamic model for sewer/channel network systems. J. Hydrualic Eng., 124, 307-315.
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