Overview:
Channels are the fundamental objects of the DSM2 grid. The Channels table allows you to enter channel connectivity, parameters and geometry.
Channels connectivity is defined by an upstream and downstream node numbers
of the channels. Two child tables describe the locations and geometry
of user-described cross-sections in the selected channel. Note that a default initial condition is
required for every channel number in the DSM2 grid, and this is entered seperately in the
Channel Initial Conditions table.
Tables:
CHANNEL
The CHANNEL table defines the connectivity, length, friction and
dispersion characteristics of a channel.
Field Descriptions
- CHAN_NO
- Channel number. This is the identifier of the channel,
and corresponds to the number you typically see on a grid map.
- LENGTH (ft)
- Length of the channel reach
- MANNING
- Manning's n friction coefficient for the whole reach.
- DISPERSION
- Dimensional dispersion factor.
- UPNODE
- Number of the upstream node at which channel is
connected.
- DOWNNODE
- Number of the downstream node at which channel is
connected.
Table Info
- Identifier:
- CHAN_NO
- Parent Table:
- Table is parent
- Include Block:
- GRID
XSECT
This table lists files where bathymetric
cross-sections are specified by the user using the CSDP format.
The table lists the fraction of the distance
along the reach (from upstream to downstream) at which the user
cross-section is located. These cross-sections will be interpolated by
the model at computational points. Overspecification of geometry is a
frequent source of user error/misconception,
please see usage notes below. Also
note that this style of input and the XSECT_LAYER "single file"
format below should not be freely mixed for a given channel -- use
one or the other.
Field Descriptions
- CHAN_NO
- Channel number where cross-section is located
- DIST
- Fraction of distance from upstream node to downstream node where cross-section is located
- FILE
- CSDP-formatted file where cross-section geometry is defined.
Table Info
- Identifier:
- CHAN_NO, DIST
- Parent Table:
- CHANNEL
- Parent Identifier:
- CHAN_NO
- Include Block:
- GRID
XSECT_LAYER
The Cross-Section Layer Table lists geometric information
about each cross-section. This information is in the form of lookup
tables of hydraulically important quantities such as area, width and
wetted perimeter.
Field Descriptions
- CHAN_NO
- Channel number in which cross-section is located.
- DIST
- Fraction of distance from upstream node to downstream node where cross-section is located
- ELEV
- Elevation from bottom at which properties are known. The area, width, etc. apply to this elevation, and channel properties between elevations are linearly interpolated.
- AREA
- Area of channel from bottom to cross section(sq ft). Ignored if Area disagrees
with the integral of WIDTH.
- WIDTH
- Width of channel at top (ft).
- WET_PERIM
- Wetted perimeter of channel at given elevation.
Table Info
- Identifier:
- CHAN_NO, DIST, ELEV
- Parent Table:
- CHANNEL
- Parent Identifier:
- CHAN_NO
- Include Block:
- GRID
Examples:
CHANNEL with XSECT_LAYER cross-section
CHANNEL with XSECT (csdp) cross-section
Usage Notes:
- All channels must have an initial condition and at least one cross-section.
- Older versions of DSM2 had the notion of a "regular" cross-section (meaning rectangular). In the current DSM2 this is just a cross-section with two layers.
- Users frequently overspecificy cross-sections, either by specifying
more cross-sections longitudinally than the model can possibly use
or by describing cross-sections vertically in such a way as to capture highly local features
such as small constrictions, sills and undulations. DSM2 is commonly used with spatial resolution (delta x)
of several thousand feet. You should only include features that are well resolved by this resolution, which means
changes that persist over several miles. Even more importantly, you should avoid adjacent cross-sections with bottoms
that vary greatly in elevation because they can cause odd behavior when cross-sections are interpolated to
computation points. The bottoms layers of cross sections should represent the "overall" slope of the channel.