Glossary and Common Terms

Search this article for definitions of terms commonly used throughout the 2Nform platform. If you don't see what you're looking for, let us know!

Note: If you are looking for our Structural BMP types, please go here

 

Table of Contents

General

2Nform Software

Structure Features

Trash Amendments

Trash Full Capture Systems

Trash Visual Assessments

 

General

Landsat ARD grid
The 30m grid cell used in the 2NFORM Trash Module Analysis is equivalent to 1 pixel in the US Landsat Analysis Ready Data (ARD) dataset, which uses a common tiling scheme (i.e., US Landsat ARD grid) developed by the USGS to process over 40 years of satellite imagery.

MS4  (Municipal Separate Storm Sewer System)
Municipal Separate Storm Sewer System (MS4) includes ditches, curbs, gutters, storm sewers, and similar means of collecting or conveying urban derived stormwater runoff that do not connect with a wastewater collection system or treatment plant. An MS4 is typically operated by a public agency such as a city, county, municipal utility district, transportation district, or state or federal agency. MS4s operate under a NPDES stormwater discharge permit to satisfy the water quality requirements of the Clean Water Act.

NPDES (National Pollutant Discharge Elimination System)
National Pollutant Discharge Elimination System (NPDES) permit program regulates water pollution through the regulation of municipal and industrial wastewater non-point sources that discharge pollutants into the waters of the US.

Receiving Water
The waters to which the MS4 catchments and outfalls drain. The National Hydrography Dataset (NHD) is the recommended layer to define the receiving waters within the MS4. Receiving waters identified in the NHD are developed by and available from the USGS.

Urban Catchment
A contiguous planning unit that represents the hydrologic routing of urban lands within the MS4.

Urban Drainage
An area within an MS4 that drains to a terminal, discrete catchment. Urban drainages contain all upstream discrete and distributed catchments but must terminate with a discrete catchment draining to a receiving water or to a distributed catchment.

Discrete Catchment
A discrete catchment possesses a singular point at the downstream boundary of the
catchment into either another catchment or a receiving water. This point may be a stormwater outfall or unobservable in the case where the singular point is a subsurface pipe, juncture of the storm drain system, or an above-ground channel. Whether observable or not, all rain falling within the catchment exits the catchment as stormwater runoff, flows through this single point.

Distributed Catchment
A distributed catchment possesses more than one outfall at the downstream boundary of the catchment into either another catchment or a receiving water. Stormwater can be routed across the catchment boundary by any combination of sheet flow, overland flow, channels, culverts etc. A distributed catchment could be delineated into several smaller discrete catchments, but to achieve the target urban catchment size, neighboring areas draining to the same downstream catchment or receiving water are grouped to make a single distributed urban catchment.

Stormwater Outfall
Any point where a separate storm sewer system discharges to a receiving water.

Flow Direction
A point where stormwater flow is exiting a discrete catchment into either another catchment,
a receiving water, or outside the MS4 boundary. These points are created when discrete catchments do not end in an outfall, but rather a subsurface pipe (or similar). These are typically created when urban drainages are subdivided into urban catchments. Distributed catchments do not contain flow direction points.


2NFORM Software

2Nform
A purpose-built stormwater software solution for MS4s to conduct smart inspections, communicate environmental benefits and simplify regulatory compliance. 2NFORM is comprised of multiple data collection and management modules that inform the work flow of stormwater managers and supporting staff and summarize annual progress under the MS4 permit in compliant annual reporting formats.

BMP RAM
The Structural BMP Maintenance Rapid Assessment Methodology (BMP RAM) is a comprehensive and repeatable field observation methodology to simplify how municipalities inventory, assess effectiveness, and determine maintenance intervals of structural BMPs. The standardized 0-5 scoring and mapped results are used to simply communicate the relative effectiveness of any stormwater structural BMP. BMP RAM results inform swTELR estimates of catchment runoff and pollutant load reduction estimates.

Benchmark
The desired and achievable condition of any structure or landscape feature, equivalent to a RAM score of 5.0. In most instances, benchmark condition may be observed and measured shortly following construction or immediately following appropriate maintenance actions.

Construction Module
2NFORM’s Construction Module is a comprehensive and repeatable field inspection and data management tool to simplify how municipalities inspect, track and report compliance with construction regulations, including those subject to the Construction General Permit.

Conveyance Structure
A structure designed to convey stormwater downgradient in a manner than mitigates, and does not induce, localized flooding. Most structural BMPs convey stormwater and treat stormwater by reducing runoff volumes or reducing pollutant concentrations, or both.
Drop inlets and trash traps are conveyance structures, but not structural BMPs.

Field Observations
The protocols performed in the field to populate the field data entry form. Observations vary by where they are being conducted (structure, landscape feature and project) and the intent (performance assessment, maintenance urgency, or inspection checklist).

Inventory
The process of locating a structure, landscape feature or project and providing feature-specific information critical to tracking and estimating performance.

Low Impact Development Module
2NFORM’s Low Impact Development (LID) Module is a comprehensive and repeatable field inspection and data management tool to simplify how municipalities inspect, track and report compliance with regulations that require low impact development integration in urban development and redevelopment projects.

Parcel RAM
The Parcel Rapid Assessment Methodology (Parcel RAM) is a repeatable field observation methodology to assess and objectively verify parcel condition. Parcel condition is the observable relative water quality threat of a parcel at time of observations should a runoff event occur. Effectively implemented nonstructural and structural BMPs can improve parcel condition. In swTELR, these modeled conditions reduce runoff generated from parcels.

Reporting & Planning Module
2NFORM’s Reporting & Planning Module is a web-based data management, analytics and reporting tool that synthesizes the other module information and assessment results. Users view quantified progress towards compliance milestones in maps, tables and charts, submit annual reports to regulators, and create planning scenarios to compare the benefits associated with future water quality improvement actions.

Road RAM
The Road Rapid Assessment Methodology (Road RAM) is a repeatable field observation method to assess and objectively determine the relative downslope water quality threat from a paved or unpaved road.

Structural BMP
Structural BMPs are any structure designed to treat urban stormwater from a known drainage area for a given size design storm. Structural BMPs accept, attenuate, and treat urban stormwater and are implemented to reduce pollutant loads in stormwater by reducing runoff volumes or reducing pollutant concentrations or both. BMP RAM defines 15 distinct structural BMP types categorized by the processes relied upon for water quality improvements and relative treatment capacity.

Structural BMP Module
2NFORM’s Structural BMP Module is a comprehensive and repeatable field inspection and data management tool to simplify how municipalities inspect, track and report compliance with MS4 permit requirements related to structural BMPs. BMP RAM is a customized repeatable assessment method to rapidly document structural BMP effectiveness and determine maintenance urgency.

swTELR
The stormwater Tool to Estimate Load Reductions is a purpose built urban hydrology and pollutant loading model that quantifies the cumulative pollutant load reductions to receiving waters from structural and non-structural urban stormwater BMPs.

Threshold
The condition of any structure or landscape feature at which it is no longer acceptable from a water quality treatment perspective. The threshold value equates to a RAM score of 2.0. Typically, threshold values for field observations are stored as default values relative to benchmark values.

Trash Module
2NFORM’s Trash Module is a comprehensive and repeatable field inspection and data management tool to simplify how municipalities inspect, track and report compliance with urban trash control regulations. Customized repeatable assessment methods allow user to rapidly document the effectiveness of structural and non-structural trash controls as well as identify litter hot spots where additional actions are required.

Structure Features

Bypass Outlet
The outlet at which stormwater exits when the storage capacity of the structure is exceeded. Bypassed volumes are not treated and therefore no water quality benefit is associated with these flows.

Centralized
A large-scale structure treating a large urban drainage with multiple land uses and ownership. Centralized structures are typically, but not always, publicly owned and maintained.
Centralized structural BMPs include bed filter, detention basins, dry basins, infiltration basins, media filters, treatment vaults, and wet basins. Centralized FCS include bed filter, detention basins, dry basins, infiltration basins, media filters, treatment vaults, and trash traps.

Decentralized
A small-scale structure designed typically to treat smaller impervious areas. Decentralized structures often accept runoff from a single land use drainage area and are associated with (re)development and roadside projects.
Decentralized structural BMPs include biofiltration, bioretention, bioswale, filtration device, infiltration feature, pervious pavement, sediment trap, and settling basin. Decentralized FCS include biofiltration, bioretention, drop inlet, filtration device, infiltration feature, sediment trap, and settling basin.

Footprint
Surface area (sq-ft) of a designed structure that will typically be inundated; approximately the area at the average design depth.

Treatment Capacity
Storage capacity (cu-ft) below the bypass outlet, designed for water quality treatment.

Trash Amendments

100% Trash Full Capture
The goal of the California State Trash Amendments requires permittees to eliminate trash (5mm or larger) discharges to receiving waters by 2030 from all trash priority land use areas (PLUs). Full trash capture can be achieved through either structural or non-structural trash controls with the MS4 required to collect data and demonstrate progress toward this goal.

1yr, 1hr Storm Event
The rainfall depth accumulated during a 1-hour period expected to occur once per year on average. This is the design storm used in the CA state definitions of trash full capture systems (FCS). NOAA provides precipitation frequency estimates for various durations and average recurrence intervals (years) for anywhere in the United States (https://hdsc.nws.noaa.gov/hdsc/pfds/).

California State Trash Amendments or Trash Provisions
On April 7, 2015, the State Water Board adopted an Amendment to the Water Quality Control Plan for Ocean Waters of California (Ocean Plan) to Control Trash and Part 1 Trash Provisions of the Water Quality Control Plan for Inland Surface Waters, Enclosed Bays, and Estuaries of California (ISWEBE Plan). Together, they are collectively referred to as "the Trash Amendments". The Trash Amendments do the following: (1) establish a narrative water quality objective for trash, (2) corresponding applicability, (3) establish a prohibition on the discharge of trash, (4) provide implementation requirements for permitted storm water and other discharges, (5) set a time schedule for compliance, and (6) provide a framework for monitoring and reporting requirements. Following adoption, the Trash Amendments were submitted to both the California Office of Administrative Law (OAL) and the U.S. Environmental Protection Agency (U.S. EPA) for review and approval. The OAL approved the Trash Amendments on December 2, 2015. The U.S.EPA approved the Trash Amendments on January 12, 2016.
All California municipal separate storm sewer (MS4) discharge permit holders include requirements to demonstrate compliance with the State Trash Amendments at some stated future date in their respective MS4 permits or supplemental State Water Board orders, generally within the next decade.

Multi-benefit Treatment System
A non-proprietary structural BMP that was not purposely designed and installed to meet the CA Water Board definition of FCS and rather installed to reduce volumes and/or other urban pollutants. However, either in its original configuration or through retrofit actions the structure does trap all debris 5mm in size up to the 1yr/1hr storm. During the FCS inventory process, users upload documentation to justify the designation of the structural BMP as a FCS.
These may include the following 2NFORM structural BMP types: bed filter, biofiltration, bioretention, detention basin, dry basin, infiltration basin, infiltration feature, and settling basin.

Track 1
Permittees intend to eliminate urban litter discharge to local receiving waters by treating all trash priority land use (PLU) areas using structural controls (trash full capture systems; FCS) that treat the 1yr/ 1hr storm intensity for material greater than 5mm in size.

Track 2
Permittees intend to eliminate urban litter discharge to local receiving waters by treating all trash priority land use (PLU) areas using a combination of structural (trash full capture system; FCS) and non-structural controls such as effective street sweeping programs, community clean-ups, litter prevention campaigns, etc. Track 2 permittees require a method to demonstrate and report areas treated by non-structural controls are indeed effective (i.e., trash full capture system equivalency; FCSE).

Trash Full Capture
Demonstration that an urban area is not a source of trash to stormwater entrainment and delivery to receiving waters. This can be achieved either through treatment by a functioning trash full capture system (FCS) or demonstration of no litter accumulation susceptible to stormwater transport should a rain event occur (termed trash full capture system equivalency; FCSE).

Trash Full Capture System (FCS)
A trash full capture system (FCS) is a treatment control that traps all particles 5 mm or greater and can treat the 1yr, 1hr storm event.
The Water Board maintains a list of approved trash full capture systems found here

Trash Full Capture System Equivalency (FCSE)
Full trash capture system equivalency (FCSE) is demonstrated using repeated visual trash assessments where the results indicate the area is litter free with statistical certainty equal to or above the threshold defined by the user.

Trash Priority Land Use (PLU)
Urban trash priority land uses (PLU) are defined as urban locations that are at high risk for trash generation. Permittees define these areas based on state guidance, local knowledge, and visual assessments of trash accumulation.

Trash Treatment Control Device
A proprietary structure purposely designed and installed specifically to trap all debris 5mm in size up to the 1yr/1hr storm. A trash treatment device MAY capture, treat, or transform other pollutants beyond trash. The CA Water Board maintains a Certified Full Capture System List of approved proprietary trash treatment devices and during the FCS inventory process users upload manufacture and design information relevant to the specific FCS.

Trash Full Capture Systems

FCS Assessment
A comprehensive and repeatable field observation methodology to simplify how municipalities inventory, assess effectiveness, and determine maintenance intervals of structural Full Trash Capture Systems (FCS). The standardized 0-5 scoring and mapped results are used to simply communicate the relative effectiveness of any FCS. The area draining to an FCS has achieved full trash capture if the FCS score is > 2.0 (i.e. functional).

FCS Assessment Interval
The user-defined interval (in months) at which an FCS should be inspected. The FCS assessment interval is tracked in 2NFORM and used to alert municipal staff when specific FCS assessments are due.

FCS Drainage Area
The FCS drainage area is the total area that drains to a trash full capture system (FCS). Users delineate the treated drainage area when the FCS is inventoried through the selection of polygons that drain to the FCS, and this selection should be field verified during final inspections when the FCS is installed or constructed.

FCS Exposure
Trash full capture system (FCS) exposure (open or closed) influences both the susceptibility of captured trash to mobilize outside of the device in subsequent wind or runoff events observations as well as the field personnel access to conduct specific observations.
• Open: Location where trash is captured is open to the air and potentially susceptible to wind transport. Observations of the trash density and distribution within the FCS are easy.
• Closed: Location where the trash is capture is contained and closed. Trash could not be mobilized by wind. May or may not be contained within confined space.

FCS Function
A FCS hydraulic design and function will capture and retain 5mm debris up to the 1yr/1hr storm in one of two ways. Either:
• Volume-based retention: the retention volume of the structure meets or exceeds the volume delivered during the 1yr/1hr storm and that all treated effluent is free of debris ≥ 5mm.
OR
• Flow-based treatment: the rate of stormwater flow though the FCS can accommodate up to the 1yr/1hr storm intensity and all treated effluent is free of debris ≥ 5mm.

FCS Grouping
Categorization of trash full capture systems (FCS) designated by the state to distinguish between proprietary devices (i.e., trash treatment control devices) and non-proprietary structural BMPs (i.e., multi-benefit treatment systems).

FCS Score
The trash full capture system (FCS) score is a 0-5 (± 0.1) value that represents the relative maintenance urgency of the FCS at the time of observation. The FCS score is a weighted integration of field observation results based on the FCS inventory inputs. An FCS score of 5.0 is the achievable condition or benchmark. An FCS score of 2.0 is a trigger that maintenance or repairs are required to restore the FCS to a functional state.

Functional FCS
A FCS with a current FCS score > 2.0, indicating it is effectively treating its respective treated drainage area for the 1yr, 1hr storm for mater ≥ 5mm.

Visible Screen
A 5mm screen installed within a FCS that can be directly inspected by field personnel.

Trash Visual Assessments

Low Litter
Based on available visual trash assessment data and associated results, an area may be determined to be low litter or essentially devoid of mobile trash. 2NFORM assertions of low litter areas include a measure of statistical certainty based on the available dataset. There may be a few small pieces of trash in the area, but they are not obvious at first glance.

Trash Condition
Trash condition represents the litter density expressed as one of four categories: low, moderate, high or very high. Visual trash assessments determine trash condition at time of observation and 2NFORM analytics predict the likely trash condition based on the available visual trash assessment dataset.

Trash Condition Certainty
Trash condition certainty is the statistical certainty of the expected trash condition based on the available data. Certainty is influenced by the number of observations available and variability of the results.

Urban Trash Assessment
A repeatable field observation methodology to assess trash condition within the urban landscape. Urban trash assessments can be performed along routes traveled via car, bike or walking or at specific locations representing approximately 1,000 ft2.

Stream Trash Assessment
A repeatable field observation methodology to assess trash condition within along a stream or open channel. Stream trash assessments can be performed along walking routes or at specific locations representing approximately 1,000 ft2.