Glossary

Aggradation

The process by which a Stream's gradient steepens due to increased Deposition of sediment

Alluvial

Process where transported chiefly by water and is sorted.

Alluvial Fans

A triangular deposit of sediment left by a Stream that has lost velocity upon entering a broad, relatively flat Valley

Alluvium

Transported chiefly by water and is sorted.

Bankfull

This stage is delineated by the Elevation point of incipient flooding, indicated by deposits of sand or silt at the active scour mark, break in Stream bank slope, perennial vegetation limit, rock discoloration, and root hair exposure

Bankfull Depth

(dbkf):

. The average depth measured at Bankfull Discharge.

Bankfull Discharge

(Qbkf ):

The dominant channel forming flow with a recurrence interval seldom outside the 1 to 2 year range.

Bankfull Width

(Wbkf):

. Channel width at Bankfull Discharge.

Baseflow

Stage at Average Low Flow

Baseflow Width

Wetted width at Baseflow. Critical for fisheries passage and other biotic indices.

Channel Length

Curvilinear distance measurement along the center of the channel

Channel Slope

Change in Elevation divided by the length of channel along a channel distance of 20-30 riffle/pool sequences or 2 Meander lengths. Valley Slope/Sinuosity.

Colluvial

Process where transported chiefly by gravity and is unsorted. It may travel within water

Colluvium

Transported chiefly by gravity and is unsorted. It may travel within water

Competence

A Streams ability to transport sediment. The diameter of the largest sediment grain transported

Datum

An arbitrary Elevation from which all vertical measurements are taken in a design

Degradation

The process by which a Stream's gradient becomes less steep, due to the Erosion of sediment from the Stream bed. Such Erosion generally follows a sharp reduction in the amount of sediment entering the Stream

Delta

An Alluvial fan having its apex at the mouth of a Stream

Deposition

The terminus of Erosion - the settling of particles

Elevation

Measure of vertical length relative to a Datum

Entrenchment Ratio

(ER)

. The channel width at two times the Bankfull Depth divided by the channel width at Bankfull.

Erosion

The process by which particles of rock and soil are loosened, as by weathering, and then transported elsewhere, as by wind, water, ice, or gravity

FGM

Fluvial Geomorphology

Flood-Prone Area

A relatively flat lowland that borders a Stream and is covered by its waters at flood stage of twice the maximum Bankfull Depth.

Flood-Prone Width

(WFP)

. The Stream width at a discharge level defined as twice the maximum Bankfull Depth.

Floodplain

Land that is actively (flooded beyond Bankfull once every 1-2 years), generally broad, gently sloped Valley floor, often bounded by a Terrace (abandoned Floodplain) or encroaching side slope

Geologic Material

Solid inorganic substratum of the earth and all possible derivatives

Landforms

Natural features of a land surface

Low Flow

Groundwater fed flow

Meander

Curves deviating from a linear course. Components of Meander geometry include length, amplitude, belt width.

Meander Width Ratio

Meander Belt Width divided by the Bankfull Width

Reach

A channel type unit length with the same channel type existing for a length over twenty Bankfull channel widths (Rosgen). The length of channel uniform with respect to discharge, depth, area, and slope. The length of a channel for which a single gage affords a satisfactory measure of the stage and discharge. The length of a river between two gaging stations. More generally, any length of a river.

Sinuosity

Ratio of Channel Length to Valley Length. Ratio of Valley Slope to Channel Slope.

Stream

A body of water found on the Earth's surface and confined to a narrow topographic depression, down which it flows and transports rock particles, sediment, and dissolved particles. Rivers, creeks, brooks, and runs are all Streams

Terrace

An abandoned Floodplain, due to river incision or downcutting, etc

Thalweg

Longitudinal outline/trace/survey of a deepest part of riverbed from source to mouth (upstream/downstream). Line of steepest descent along the Stream.

Valley

A depression on the earth surface drained by, and whose form is changed by, water under the attractive force of gravity, between two adjacent uplands

Valley Length

Horizontal distance measured in the Thalweg of two cross sections in a linear depression between two adjacent uplands

Valley Slope

Slope of a Valley for a given Reach where Valley and Reach intersect for some longer distance (several Meanders or step pools)

Wetted Width

The width of the wetted Stream at the time of the survey. Wetted Width is generally less than Bankfull Width. Wetted Width is also referred to as "low flow channel