Erosion and Sediment Pollution Control Program Manual.pdf

Retardance -----In grass-lined channels, it is the resistance to flow due to the vegetative lining. The
degree of vegetal retardance depends largely on the height and density of cover.
Retention -----That part of the precipitation falling on a drainage area that does not escape as surface
streamflow.
Retention Basin -----A permanent lake or pond used to prevent stormwater runoff from leaving the
development site. Storage for temporary periods is referred to a “detention.”
Retrofit -----The modification of stormwater management systems through the construction and/or
enhancement of wet pond, wetland plantings, or other BMPs designed to improve water quality.
Return Period -----The arithmetic mean of time units, such as years, between observations of an event
of a certain magnitude. For example, a storm event with a return period of 100 years is not
expected to occur more often than once in 100 years.
Revegetation -----Reestablishing vegetative cover on ground that has been disturbed, such as a
construction site.
Revetment -----1. A facing of stone, bags, blocks, pavement, etc. used to protect or armor a bank
against erosion. 2. A retaining wall.
Reynolds Number -----A number defined by the equation Re = 4 rv/
Where: Re = Reynolds number
r = hydraulic radius
v = velocity
The Reynolds number is used to determine whether a flow will be laminar or turbulent.
Turbulent flow typically has a Reynolds number greater than 4000.
Rhizome -----A below-ground stem capable of growing horizontally and producing a new plant.
Riffle -----Shallow rapids in an open stream where the water surface is broken into waves by
obstructions such as shoals or sandbars.
Right Bank -----The right-hand side of a stream, river, or channel when facing in the direction of flow.
Right-of-Way -----For highways, pipelines, and utility lines, it is the boundary line within which the
contractor has a legal right to do earthwork.
Rill Erosion -----Removal of soil particles from an area due to surface runoff moving through relatively
small channels — only a few inches deep.
Riparian -----Pertaining to the banks of a stream, river, waterway, or other flowing body of water as well
as the plant and animal communities along such bodies of water.
Riparian Buffer ----- A BMP that is an area of permanent vegetation along surface waters.
Riparian Corridor -----A narrow strip of land centered on a stream that includes the floodplain as well
as related habitats adjacent to the floodplain. Also called a riparian zone.
Riparian Forest Buffer ----- A type of riparian buffer that consists of permanent vegetation that is
predominantly native trees, shrubs and forbs along surface waters that is maintained in a
natural state or sustainably managed to protect and enhance water quality, stabilize stream
channels and banks, and separate land use activities from surface waters.
Riparian Rights -----A principle of common law that requires any use of waters adjoining or flowing
through his lands must so use and protect them so that he will enable his neighbor to utilize the
same waters undiminished in quantity and undefiled in quality.
Riparian Vegetation -----Plants adapted to moist growing conditions found along waterways and
shorelines.
Riprap -----Crushed stone that meets certain requirements for size gradation, weight, durability, and
shape. It is generally specified according to “R” size.
Riprap Apron -----A type of outlet protection constructed out of riprap and with dimensions derived
from Figure 9.3 or 9.4.
Riser -----That part of a barrel/riser type spillway which extends vertically from the bottom of the
impoundment to the top of the settling zone. See Figure 7.1.
River Training Works -----Structures placed within a stream channel to direct the current into a
predetermined course.
Rivulet -----A small stream or brook.
Road Maintenance Activities -----Earth disturbance activities within the existing road cross-section or
railroad right-of-way including: shaping or re-stabilizing unpaved roads; shoulder grading; slope
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