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Upper Midwest Environmental Sciences Center

1989 & 91 Aquatic Areas Data

Legend Information


The following is an excerpt from the report An Aquatic Habitat Classification System for the Upper Mississippi River System, written by Daniel B. Wilcox. This document contains excerpts from that report, (1) general terms used to describe aquatic habitats, and (2) terms used to attribute the aquatic area data sets.

General Terms

Reference River Discharge: The reference river discharge is the discharge level exceeded 50% of the time at point of interest.

Reference Water Surface: The reference water surface is the water surface elevation profile associated with the reference river discharge.

Aquatic: Floodplain Terrestrial A distinction is made between floodplain areas that are normally aquatic and areas that are normally terrestrial at the reference discharge level. At times of higher river discharge, more of the floodplain is inundated and becomes aquatic habitat. Above the reference discharge level, portions of the floodplain that are normally terrestrial can be described according to their elevation, frequency, and duration of inundation.

Channel - Backwater: A distinction is made between channel areas and off-channel or backwater areas.

Channels: Channels in the Upper Mississippi River System (UMRS) include the main channel, secondary and tertiary channels, tributary channels, and excavated channels. Within the main channel (and some secondary channels) are the designated navigation channel, sandbar, channel border, and tailwater areas. Within channel border areas are natural bank areas and areas associated with channel-training structures.

Backwaters: Backwaters are areas of the UMRS that are beyond the banks of the main and secondary channels. Backwaters include a variety of alluvial floodplain waterbodies. Tertiary and smaller tributary channels are included in backwater areas.

Contiguous, Isolated: A distinction is made between contiguous (connected by surface flow with the main channel) and isolated backwaters.

Vertical Dimension: Depending on study needs, aquatic habitat in the UMRS can be defined according to vertical spatial categories. Within aquatic areas are the water surface, the water column, the surfaces of cover structures such as aquatic macrophytes, rocks, and woody debris, the interior of cover structures, the sediment surface, the hyporheic zone within the sediment, and the deeper sediment.

Aquatic Areas: Aquatic areas are spatially large areas of somewhat similar aquatic habitat defined according to geomorphic and navigational features of the river.

Habitat Conditions: Habitat conditions are physical and chemical variables that occur in aquatic habitat.

Habitat Types: Habitat types are defined as needed for the application, using aquatic area and some combination of habitat conditions. No formal classification of aquatic habitat types is proposed. Habitat type definitions can be developed according to the needs of different investigations.


Data Set Attributes:

Main Channel: The main channel conveys the majority of the river discharge and in most reaches includes the navigation channel. Boundaries of the main channel are the apparent shorelines (the land/water boundaries visible from aerial photographs taken at the reference discharge level), straight lines across the mouths of secondary, tributary, and tertiary channels, and along the top of inundated portions of the natural bank line.

Navigation Channel: The navigation channel is the designated navigation corridor marked by channel buoys (Fig. A-1). In reaches where buoys are not used, the centerline of the navigation channel is defined by lights and daymarks on shore that pilots use for navigation. The navigation channel on most of the UMRS is 91.4 m (300 ft) wide in straight reaches and 152.4 m (500 ft) wide in bends. The navigation channels in the upper pools of the UMRS and tributary waterways are narrower. The prescribed width and depth of at least 9 ft (2.6 m) are maintained by the navigation dams and by dredging where necessary. The navigation channel extends through the locks at each lock and dam. The navigation channel is usually in the main channel but in some reaches, it is located in secondary channels.

Tailwaters: Tailwaters are the areas downstream of the navigation dams with deep scour holes, high velocity, and turbulent flow. Boundaries of tailwater areas are the navigation dam upstream, the apparent shorelines, and a straight line across the channel 500 m downstream of the dam.

Channel Border: Channel borders are the areas between the navigation channel and the river bank. Boundaries of channel border areas are the apparent shorelines, the navigation channel buoy line, straight lines across the mouths of secondary and tertiary channels, and the inundated portions of the natural bank line.

Wing Dam: Wing dams are stone and brush channel-training structures that extend laterally into the main and secondary channels to concentrate flow into the navigation channel. The boundaries of wing dam areas are defined by proximity to wing dam structures. The landward boundaries are the apparent shorelines and inundated portions of the natural bank line. The upstream and downstream boundaries of wing dam areas are parallel to and 50 m from the wing dam structures. The riverward boundaries are perpendicular to the riverward end of the wing dams.

Closing Dam: Closing dams are stone and brush channel-training structures that were built across channels to concentrate flow into the navigation channel. Boundaries of closing dam areas are parallel to and 50 m upstream and downstream of the structures. Where closing dams are close to the main channel border, the upstream boundary is across the mouth of the channel. The lateral boundaries are the apparent shorelines of the channel.

Revetted Bank: Revetted banks are the armored shorelines of the main and secondary channels. Revetment on the UMRS is rock riprap or articulated concrete mats. Shorelines with concrete or steel bulkheads or paved levees are included in this category. In some locations, bank revetment is no longer connected to shore. Boundaries of revetted bank areas are the apparent shoreline, the upstream and downstream limits of the revetment, and a line riverward, parallel to and 15 m from the apparent shoreline. For revetments that are no longer connected to shore, the shoreward boundary of revetted bank areas is a line parallel to and 15 m from the top of the remaining revetment material.

Unstructured Channel Border: Unstructured channel border areas are areas without revetments or other channel-training structures. Boundaries of the unstructured channel border areas are the apparent shoreline, the upstream and downstream limits of other channel border areas, the downstream limits of tailwater areas, and indundated portions of the natural bank line. Depending on the application, unstructured channel border areas can be further classified according to depth gradient and geomorphic feature (point bar, inside bend, etc.).

Secondary Channel: Secondary channels are large channels that carry less flow than the main channel. In some reaches, the navigation channel is located in secondary channels. Boundaries of secondary channel areas are the apparent shorelines, straight lines across the mouths of tertiary channels, and straight lines at the upstream and downstream limits of the apparent shorelines where secondary channels connect with the main channel.

Sandbar: Sandbars are flat-sloped areas within the main and secondary channels that are characterized by sand substrate. Sandbars have side slopes of less than 1V:6.67H, are completely submerged at the 10% exceedence frequency discharge level, and are not connected to shore at the reference discharge level. Portions of sandbar zones emergent at the reference river discharge are unvegetated. Sandbar boundaries are the 2-m depth contours at the reference river discharge level and the apparent shoreline or boundaries of rock structure areas.

Tertiary Channel: Tertiary channels are small channels, 30 m wide or less. The lateral boundaries of tertiary channels are the apparent shorelines or the inundated natural bank lines. The upstream and downstream limits of tertiary channels are straight lines between the upstream and downstream limits of the apparent shorelines, or where the inundated natural bank lines merge with the surrounding bottom.

Tributary Channel: Tributary channels are channels of tributary streams and rivers. The landward boundary is the line where the tributary crosses the study area boundary. The lateral boundaries are the apparent shorelines and any inundated natural bank lines. The riverward limit of a tributary channel is a line drawn across the downstream limits of the apparent shoreline or where the inundated natural bank lines of tributary channels merge with the surrounding bottom.

Excavated Channel: Excavated channels are constructed channels with flowing water.

Contiguous or Isolated: Contiguous means hydraulically connected by surface gravity flow at reference river discharge. For mapping purposes, contiguous means having apparent surface water connection with the rest of the river. Isolated means having no hydraulic connection by surface gravity flow at reference river discharge. For mapping purposes, isolated means having no apparent surface water connection with the rest of the river.

Floodplain Shallow Aquatic: Floodplain shallow aquatic areas are portions of the floodplain inundated by the navigation dams that are not part of any channels or floodplain lakes. Floodplain shallow aquatic areas contain a mosaic of open water and emergent vegetation interspersed among islands. The boundaries of these areas are defined by the apparent shorelines and by other aquatic areas. Boundaries of floodplain shallow aquatic areas are often irregular. Where floodplain shallow aquatic areas grade into impounded areas, the boundaries will be lines connecting the downstream points of islands or peninsulas across the floodplain. Tertiary and smaller tributary channels flow through floodplain shallow aquatic areas, but the boundaries (inundated bank lines) of most of these channels can be distinguished only with bathymetric information.

Impounded: Impounded areas are large, mostly open water areas located in the downstream portions of the navigation pools. The downstream boundaries of impounded areas are the navigation dam and connecting dikes. Landward boundaries are the apparent shorelines or the boundaries of other aquatic areas. Upstream boundaries are with islands and floodplain shallow aquatic zones. Riverward boundaries are channel border zones.

Floodplain Lake: Floodplain lakes are distinct lakes formed by fluvial processes or are artificial (excavated or impounded).

Abandoned Channel Lake: Abandoned channel lakes are oxbow lakes formed by meander cutoffs, lakes formed by point bar cutoffs, and lakes formed by avulsion (a major shift in channel course). Boundaries are the apparent shorelines. The downstream boundary for contiguous abandoned channel lakes is a line that is a continuation of the apparent shoreline of the lake. Abandoned channel lakes vary greatly in size. The shape of most abandoned channel lakes reveals their origins as former channels.

Tributary Delta Lake: Tributary delta lakes are formed by the tributary deltas impounding all or part of the floodplain upstream of the mouth of the tributary. Boundaries are the apparent shorelines. For contiguous tributary delta lakes, the riverward boundary is where the (usually downstream) end of the lake joins a channel. The boundary is a line that is a continuation of the apparent shoreline of the channel.

Lateral Levee Lake: Lateral levee lakes are lakes formed by the impounding effect of natural riverbank levees. This type of lake is formed between the natural levee and the high ground that defines the edge of the floodplain of the river. Lateral levee lakes are also formed where natural levees impound tributary streams. Boundaries are the apparent shorelines and the boundaries of other more clearly delineated aquatic zones. On lakes formed at the mouth of tributary streams, the upstream boundary is the boundary of the study area.

Scour Channel Lake: Scour channel lakes are formed by the scouring of point bar swales during high flows. Scour channel lakes are generally small and crescent-shaped. Most of these aquatic areas are isolated. Boundaries are the apparent shorelines. Where contiguous, the connecting boundary is a line across the downstream limit of the apparent shorelines.

Floodplain Depression Lake: Floodplain depression lakes are generally large, shallow water bodies formed by uneven aggradation of sediment on floodplains during floods. This type of lake has even shorelines (limited shoreline development) and a shallow basin of even depth. Most of these lakes are larger than 100 ha. Boundaries are the apparent shorelines. Where contiguous, the connecting boundary is a line across the limits of the apparent shorelines.

Borrow Pit: Borrow pits are water bodies formed where material was excavated for levee or dike construction. The boundaries are the apparent shorelines or the limits of excavation. Most borrow pits are parallel and immediately adjacent to dikes or levees.

Artificial Lake: These aquatic areas are created by dikes or levees (not the main navigation dams and dike systems) or by excavation. The boundaries of artificial lakes are the apparent shorelines, and where contiguous, the connecting boundary is a line across the limits of the apparent shorelines.

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