Definitions
Best Management Practice (BMP)
A practice or combination of practices that prevent or reduce adverse
affects of stormwater runoff and/or associated pollutants.
Borings
Cylindrical samples of soil profile used to determine infiltration
capacity of soil types and ground water.
Buffer Strip
A zone where plantings capable of filtering stormwater are established
or preserved and where construction, paving and chemical applications
are prohibited.
Catchbasin
A collection structure below ground designed to collect and convey water
into the storm sewer system. It is designed so that sediment falls to
the bottom of the catchbasin and not directly into the pipe.
C.C.C.D.
Calhoun County Community Development
Check Dam
An earthen, rock or log structure used in grass swales to reduce water
velocities, promote sediment deposition and enhance infiltration.
County Drain
An open or enclosed stormwater conveyance system that is under the legal
jurisdiction of the Drain Commissioner for construction, operation and
maintenance.
Culvert
A conduit used for the passage of surface water under a road or other
embankment.
DEQ
Department of Environmental Quality
Design Storm
A rainfall event of specified size and return frequency(i.e., a storm
what has the likelihood of occurring once every 10 or 100 years) that is
used to calculate the runoff volume and peak discharge rate.
Detention
The temporary storage of storm runoff to control peak discharge rates
and provide gravity settling of pollutants.
Detention Basin
An area designated to temporarily store storm runoff so a controlled
outflow can slowly empty the area.
Detention Time
The amount of time that a volume of water will remain in a detention
basin.
Developer
Anyone who organizes the actual development of land and may or may not
be the landowner.
Discharge
The rate of flow(the volume of water passing a point in a given period
of time) leaving an area usually expressed as cubic feet per second.
Drainage Area
The total tributary area of a watershed usually expressed in square
miles, acres or square feet.
Drainage Facility
Any facility used to transport or store stormwater.
Drawdown
The gradual reduction in water level in a basin due to the combined
effect of infiltration and evaporation.
Easement (also know as a "Right-of-Way")
A legal right granted by a property owner to another entity giving that
entity limited use of the property involved for a specific purpose. The
Drain Commissioner secures temporary and permanent easements adjacent to
county drains for the purpose of construction and maintenance access.
Erosion
The wearing away of the land surface by wind, water, ice and gravity
dislodging soil particles. Evidence of erosion are gullies, rills,
sediment, plumes, etc.
Fill
Added earth which changes the contour of the land.
Filter Fabric
Textile or relatively small mesh or pore size that is used to 1) allow
water to pass through while keeping sediment out (permeable), or 2)
prevent both runoff and sediment from passing through (impermeable).
First Flush
The delivery of a highly concentrated pollutant loading during the early
stages of a storm due to the washing effect of runoff on pollutants that
have accumulated on the land.
Flood Plain
For a given flood event that area of land adjoining a continuous
watercourse that has been covered temporarily by water.
Freeboard
The space from the top of an embankment to the highest water elevation
expected for the largest design storm to be stored. The space is
required as a safety margin in a pond or basin.
Geotextile
A woven fabric capable of passing water but able to hold back soil.
Groundwater
Naturally existing water beneath the earth’s surface between saturated
soil particles and rock that supplies wells and springs.
Groundwater Level
The upper surface or top of the saturated portion of the soil or bedrock
layer that indicates the uppermost extent of groundwater.
Infiltration Rate
The absorption of water into the ground expressed in terms of
inches/hour.
Infiltration Capacity
The maximum rate at which the soil can absorb falling rain or melting
snow. Usually expressed in inches/hour or centimeters/second.
Invert
The interior surface of the bottom of any pipe.
Manhole
A structure that allows access into a stormwater drainage system.
Mulch
A natural or artificial layer of plant residue which aids in seedling
germination by reducing the temperature fluctuations, holding moisture
and holding soil in place.
Natural Wetland
Land characterized by the natural presence of water sufficient to
support wetland vegetation.
Non-Point Source Pollution
Pollution that is not identifiable to any particular source as described
by the NREPA.
NREPA
Natural Resources & Environmental Protection Act, Act 451 of the Public
Acts of 1994, as amended.
Off-site Detention
Detention provided at a regional detention facility as opposed to
storage on-site.
On-Site Detention
Where stormwater is detained on a site verses a regional location.
One Hundred Year Flood
A flood that has one percent (1%) chance occurring in any given year.
Ordinary High Water Mark
The line between upland and bottomland which persist through successive
changes in water level below which the presence of water is so common or
recurrent that the character of the soil and vegetation is markedly
different from the upland.
Peak Discharge
The maximum instantaneous rate of flow during a storm usually in
reference to a specific design storm event.
Permeable
Ability to absorb water.
Petition
A legal request to the Drain Commissioner to perform a maintenance
improvement or construction.
Plat
A legal procedure whereby a larger piece of property is divided into
smaller sections and is accompanied by a full description of the
original property the dimension of each lot to be subdivided and all
relevant deed restrictions and easements as described in the Land
Division Act.
Project Engineer
A professional engineer licensed in Michigan that performs the
engineering design for the development.
Proprietor
Any person, firm, association, partnership, corporation or any
combination thereof that owns property proposed for development.
Protected Wetland
Any wetland protected by state law or local government regulation.
Rational Formula
A simple technique for estimating peak discharge rates for very small
developments based on the rainfall intensity, watershed time of
concentration and runoff coefficient.
Retention
The holding of runoff in a basin without release except by means of
evaporation, infiltration or emergency bypass.
Retention Basin
A stormwater management basin that captures storm water runoff and does
not discharge directly to a surface water body. The water is
"discharged" by infiltration or evaporation.
Rip-Rap
A combination of large stone, cobbles and boulders used to line
channels, stabilize banks, reduce runoff velocities or filter out
sediment.
Riser
1. A vertical pipe extending from the bottom of a basin that is used to
control the discharge rate from the basin for a specified design storm.
2. A pipe rising from underground tile to allow surface water to enter
the tile in a low area.
Runoff
The excess portion of precipitation that does not infiltrate into the
ground but "runs off" and reaches a stream, water body or storm sewer.
Runoff Coefficient
The ratio of the amount of water that is NOT absorbed by the surface to
the total amount of water that falls during a rainstorm.
Seasonal High Water Ground Level
The highest level of groundwater that occurs frequently enough for the
water to stain the soils.
Sediment
Soil material that is transported from its site of origin by water. May
be in the form of bed load (along the bed), suspended or dissolved.
Sheet Flow
Runoff which flows over the ground surface as a thin even layer, not
concentrated in a channel or pipe.
Soil Group, Hydrologic
A classification of soils by the Natural Resource Conservation Service
into four runoff potential groups. The groups range from A soils, which
are very permeable and produce little runoff, to D soils which are not
very permeable and produce much more runoff.
Spillway
A depression in the embankment of a pond or basin used to pass peak
discharges in excess of the design storm.
Stream
By MDNR definition; "a river, creek, or surface waterway that may or may
not be defined by Act 40, P.A. Of 1956: has definite banks, a bed, and
visible evidence of continued flow or continued occurrence of water,
including the connecting water of the Great Lakes".
Swale
A natural depression or wide shallow ditch used to temporarily convey,
store, or filter runoff.
Time Of Concentration
The time it takes for surface runoff to travel from the hydraulically
farthest portion of the watershed to the design point.
Tributary Area
The entire land, including adjacent property that produces runoff to a
given point in the stormwater conveyance system or a storage basin.
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Drain Commissioner
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