Glossary / Acronyms

BDS Bureau of Development Services  
BMP Best Management Practice  
EMC Event Mean Concentration: averaging the influent and effluent concentrations for storm events, and then calculating the median change  
ESD Environmental site design  
LID Low Impact Development  
MDCIA Minimizing directly connected impervious areas  
PAC Presumptive Approach Calculator only goes up to 1ac facility. More than that and you must use same principles and Performance Approach.  
UIC Underground Injection Control  
WQCV water quality capture volume = a*(0.91*I3-1.19*I2+0.78*I) a: varies depending on drain time 6hrs: a=0.7, 12hrs a = 0.8, 24hr  a = 0.9, 40 hr a=1.0 (UDFCD).


10yr storm A storm size likely to occur once in 10 years. This is different for different regions. In the City of Portland, OR this is definited as 3.4in/24 hrs.
Class SA waters (NC) These are waters assigned for certain "designated uses". Each State is responsible for selecting these uses so they differ throughout the country. In North Carolina (the context of this term in SWAMP) this is defined as tidal salt waters that are used for commercial shellfishing or marketing purposes and are also protected for all Class SC and Class SB uses.  All SA waters are also HQW (High Quality Waters) by supplemental classification.
Class V Wells Wells which inject non-hazardous fluids, such as some stormwaters, underground.
Conveyance System A facility designed to transport water from one point to another.
CN (Curve Number) A curve number is a representation of a piece of land's runoff production based on characteristics such as hydrologic soil group, land cover type, antecedent runoff condition and hydrologic condition.
Exfiltration When water is allowed movement through the base material and into the soil underneath. *Synonymous with "infiltration".
First Flush The first runoff from a storm. This usually carries the most debris and pollutants especially if after an extended dry period.
Forebay A pretreatment facility for BMPs designed as a small pool to catch sediment.  In many cases this reduces the need for maintenance on the entire BMP which often requires dredging. Instead, only the forebay needs to be regularly cleaned. A much easier and simplified process than for the entire BMP.
Groundwater Water beneath the ground surface. It can provide water for wells and water levels can fluctuate as they are replenished by precipitation, streams and other waterbodies.
Growing Medium Soil, organic matter and sands  mixed to provide a medium for plant growth.
Hydraulic Gradient The rate of change of pressure head per unit of distance of flow at a given point and in a given direction.
i Total imperviousness ratio  Iwq/100 (UDFCD)
Ia Total percent of Watershed Imperviousness (UDFCD)
Iwq Percent to use with WQCV (UDFCD)
Impervious Surface A surface water cannot pass through. This includes roofs and pavement, however, compacted gravel roads can also be considered impervious.
Infiltration The process of water moving into and through a ground surface. It is often expressed as a rate (in/hr). . *Synonymous with "exfiltration".
ksat Saturated Hydaulic Conductivity: A fluid's ability to flow through a porous medium under saturated conditions. Ksat is reported in distance/time such as m/sec. The higher the ksat, the faster a fluid flows through a medium. This can vary greatly with a small area.
Level 1 Design Standard Design: Runoff reduction and pollutant levels reflect the median research values.
Level 2 Design Enhanced Design: Runoff reduction and pollutant levels reflect the 75th percentile research values.
Off Line Facility A facility designed using a flow regulator (i.e. diversion structure, flow splitter, etc) to obtain a specified flow rate. Flow regulators are typically used to divert the water quality volume (WQv) to an off-line structural control sized and designed to treat and control the WQv.  After the design runoff flow has been treated and/or controlled, it is returned to the conveyance system.
On line Facility A facility designed to receive, but not necessarily control or treat, the entire runoff volume of a storm event.  Online structural controls must be able to handle the entire range of storm flows.  If the facility can not handle all storm events, the excess water should be bypassed through an alternative facility.
Partial Exfiltration This technique can be used when complete exfiltration can not be achieved for any number of reasons. In this case, the underdrain of a bioretention area only is only installed on part of the bottom of the system. Various designs include installing a perforated at different levels within the facility. If installed at the bottom, exfiltration may be reduced because the pipes will collect runoff prior to entering soils. This may also have an effect on WQ because runoff will not settle for a longer period of time. A pipe near the top allows runoff time to settle at the bottom of the facility and infiltrate into the soils. Runoff will only be collected in the pipe system if water levels become high enough.
Q discharge rate (ft3/sec)
Rational Formula Q= C*I*A (Q= flow in cubic feet/sec, C= runoff cooefficient which is .9 for paved surfaces, I = intensity (2.86 in/hr for 10yr storm event and concentration time of 5min), A= area in acres)
Rational Method A method used to size stormwater facilities using the rational formula.
Roil Made liquid muddy or turbid.
Silt trap A hole or basin that settles water and allows silt/sediment to settle. Similar to a Forebay.
Surcharge volume WQC volume of water above permanent pool.
UIC Underground Injection Control. This program protects groundwater, especially those aquifers used for drinking water, from contamination under the Safe Drinking Water Act. Some underground stormwater facilities may need a special permit for intallation.
Water Table The upper level of water beneath the ground surface. It is determined by well water levels and can fluctuate similar to groundwater.
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