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Ahupua`a: An "Ahupua`a" is the Hawaiian word that comes closest to the meaning of watershed. The Hawaiians were masters of land and resource management through their concept of the ahupua`a land division- a division that starts at the source (top of the mountain, or mauka) and ends at the sea, or makai. The Ahupua`a limit is the reef. The near shore waters were an important food source. Some ahupua`a principles that may be transferred to watershed planning and management include access to a complete resource base, reverence for water, respect for all living things, coordination and cooperation, intergenerational learning, `ohana among people, and the connection between people and the land.
Best Management Practices or BMPs: Pollution control measures, applied to nonpoint sources, on-site or off-site, to control erosion and the transport of sediments and other pollutants which have an adverse impact on waters of the state. BMPs may include a schedule of activities, the prohibition of practices, maintenance procedures, treatment requirements, operating procedures, and practices to control site runoff, spillage or leaks, or drainage from raw material storage.

Silt Fence

Retention Basin

Debris Basin


Spill Kit
Biodegradable: Capable of being decomposed (broken down) by natural biological processes.
Catch basin: Curbside opening that collects rainwater from streets and serves as an entry point to the storm drain system. With more than 20,000 catch basins and over 670 miles of storm drains to clean and maintain, the City and County of Honolulu needs your help to stop pollutants from entering the storm drain system.



Channelization: The straightening and/or surfacing of streams to permit water to move rapidly and/or directly downstream.

Clean Water Act: The Clean Water Act (CWA) is a federal law that governs the discharge of pollutants into surface waters. In 1972, the CWA amended the Federal Water Pollution Control Act of 1948, with the goal to make US waters clean enough to be swimmable and fishable. To do this, the CWA established the National Pollutant Discharge Elimination System (NPDES) program to regulate the discharge of pollutants to US waters. For more information, click here.
Culvert: Concrete or corrugated steel drainage pipes used to convey water under structures such as roads, highways, or bridges.
Detention basin: A detention basin is an open area that is used for the temporary storage of excess storm water, and is designed to slowly drain at a controlled rate.
Discharge: Deposit, disposal, injection, dumping, spilling, leaking or placing of any substance into a drainage facility or natural watercourse.
Downspout: A pipe that directs stormwater runoff from the roof of a house to the ground.
Erosion: Wearing away of the ground surface as a result of action by wind and/or water.
Estuary: Body of water at the lower end of a river and which is connected to the ocean or semi-enclosed by land. In an estuary, sea water is measurably diluted by fresh water from the land. A coastal region of convergence or interaction between rivers and nearshore ocean waters where tidal action and river flow create a mixing of fresh water and salt water. These areas may include streams and marshes. Pouhala Marsh is one example. The Ala Wai Canal is an artificial estuary.
"First Flush": The first big rain after an extended dry period that flushes out the accumulated pollutants in the storm drain system and carries them straight to the ocean. “First flush” also refers to the initial portion of surface runoff during a storm. Water pollution is typically more concentrated during this time than during the rest of the storm.
Floatables: Pollutants that float on the water surface such as trash and debris.
Grassed Swales: An infiltration/filtration method that is usually used to provide pretreatment before runoff is discharged to treatment systems. Grassed swales are typically shallow, vegetated, man-made ditches designed so that the bottom elevation is above the water table to allow runoff to infiltrate into ground water. The vegetation or turf prevents erosion, filters sediment, and provides some nutrient uptake (USDA-SCS, 1988). Grassed swales can also serve as conveyance systems for urban runoff and provide similar benefits.
Green Infrastructure: A design element for a property that uses landscaped systems or manmade engineered systems and mimics natural systems.
Gutter: The edge of a street (below the curb) designed to drain water runoff from streets, driveways, parking lots, etc. into catch basins. An area formed by the curb and the street to prevent flooding by channeling runoff to the storm drains.


Heavy metals: Naturally occurring metal elements including cadmium, chromium, lead, mercury, arsenic, nickel, etc. Can also be found in sewage sludge and urban runoff. Many are toxic at low concentrations and tend to accumulate in the food chain.
Hydrology: The way water moves over the land and through the ground.
Illicit discharge: Any disposal, either intentionally or unintentionally, of material(s) or waste(s) that can pollute storm water or urban runoff.
Illegal connection: An illegal connection is the point at which a private drainage system conveys a concentrated flow to the City’s MS4 without a storm drain connection license issued to the property owner. The City’s MS4 includes the City’s piped drainage system, channels, streams, and even the curbs and gutters on a City street. All connections to the City’s MS4 require that the property owner obtain a private storm drain connection license. For more information on storm drain connections, see Revised Ordinances of Honolulu Section 14-12.12.
Impervious (nonpermeable) surface: Paved surface or other land cover that does not allow water to be absorbed into or through the surface.
Infiltration: The process by which water is soaked into the soil.
Low Impact Development (LID): A stormwater management and land development strategy used at the lot and subdivision scale that uses thoughtful land use planning and onsite natural features with small-scale stormwater controls to try to match the way the stormwater traveled over and through the landscaping before development.  Examples of LID designs include downspouts that outlet to landscaped areas, utilizing permeable hardscapes, creating a rain garden, collecting runoff in a rain barrel, and using native plants as ground cover.
Maximum Extent Practicable (MEP): Economically achievable measures for the control of the addition of pollutants from existing and new categories and classes of nonpoint sources of pollution, which reflect the greatest degree of pollutant reduction achievable through the application of the best available nonpoint source pollution control practices, technologies, processes, siting criteria, operating methods or other alternatives. 
Municipal Separate Storm Sewer System (MS4): The Municipal Separate Storm Sewer System (MS4) is the City’s storm drain system.  The MS4 includes the City’s piped drainage system, channels, streams, and even the curbs and gutters on a City street.  An MS4 is designed for collecting or conveying stormwater only, and discharges to US waters.
National Pollutant Discharge Elimination System (NPDES) permit program: The NPDES permit program was established by the Clean Water Act to regulate water pollution.  The program requires that anyone discharging pollutants from a point source to a body of water obtain an NPDES permit.  In Hawaii, this permit is acquired through the State Department of Health (DOH).

Since the City’s Municipal Separate Storm Sewer System (MS4), or drainage system, discharges directly to streams and the ocean, the City is required to obtain an NPDES permit.

Other typical NPDES permits include permits issued to a property owner for storm water discharge associated with industrial activity, or for discharge of any pollutant from a point source into state waters through the City's MS4.  For construction, NPDES permits are issued for construction activity including clearing, grading and excavation activities, or for construction dewatering activity.

For more information, see Revised Ordinances of Honolulu Sections 14-12 to 14-17.

Nonpoint Source Pollution: Pollution that does not come from a single, identifiable point but from a number of points that are spread out and difficult to identify and control. Includes materials that wash from roofs, streets, yards, driveways, sidewalks as well as from agriculture, erosion, and construction. Collectively, this is the largest source of stormwater pollution.
O'opu. Mascot of the City and County of Honolulu Department of Environmental Services. Hawai'i 's streams are home to these unique fish. There are five species of native stream fish (four gobies and an eleotrid). Four are endemic (found nowhere else on earth) and one is indigenous (native to Hawai'i and other locations). Their distribution along the stream is believed to be influenced by their climbing ability. The origin of the o`opu and link to the ocean are evident in their mainly diadromous life cycle, which means "two runs", one to the ocean as newly hatched larvae and subsequent return from the ocean to freshwater as juveniles. This completes their life cycle and emphasizes the importance of maintaining the "mauka (mountain) to makai (ocean)" connection. O 'opu are recommended for use as a biological indicator of stream water quality. For example, an increase in numbers of the o ' opu would indicate improved water quality. The reason for this is that o'opu require fresh, cool, flowing water of good quality. More info and photos located here.
Outfall: Opening at the end of a storm drain system that allows water to flow into a channel, lake, river, bay or ocean.
Permeable (pervious) surface: allows water to be absorbed into or through the surface.
Plume: A visible or measurable discharge of a contaminant from a given point of origin. Can be visible, sediment, or invisible, such as thermal in water, or visible in the air as, for example, a plume of smoke.
Point Source Pollution: Pollution from a single identifiable source such as pipes or man-made ditches.  The NPDES permit program regulates point source pollution that discharge into US waters.
Pollutants: Any waste, cooking or fuel oil, waste milk, waste juice, pesticide, paint, solvent, radioactive waste, hazardous substance, sewage, dredged spoils, chemical waste, rock, sand, biocide, toxic substance, construction waste and material, and soil sediment. The term also includes commercial FOG waste as defined under the Revised Ordinances of Honolulu (ROH) Section 14-5A.1. For more information, see ROH Section 14-12.
Pollution problem The discharge of any pollutant into state waters directly or by conveyance through a drainage facility that creates a nuisance or adversely affects the public health, safety or welfare, or causes a drainage facility to violate any provisions of the City's National Pollutant Discharge Elimination System permit or violates any water quality standards of the State of Hawaii.
Rain Barrel:  A catchment system that collects runoff from a roof for reuse.

Rain Garden: A planted depression that allows rainwater runoff from impervious urban areas like roofs, driveways, walkways and compacted lawn areas to be absorbed into the earth.

Retention Basin: A retention basin is an area that stores storm water, but on a more permanent basis than a detention basin. Water often remains in a retention basin indefinitely, with the exception of the volume lost to evaporation, absorbed into soils, or pumped out.

Runoff (also known as Urban Runoff): Water from rain (stormwater), irrigation, garden hoses, or other activities that does not soak into the ground but flows over impervious areas or areas already saturated with water.  Runoff picks up pollutants (cigarette butts, trash, automotive fluids, used oil, paint, fertilizers and pesticides, lawn and garden clippings and pet waste) from streets, parking lots, driveways and yards and carries them through the storm drain system and straight to the ocean.

Sediment: Sediment includes particles of sand, clay, silt, and other substances that settle at the bottom of a body of water. Sediment can come from the erosion of soil or from the decomposition of plants and animals. Wind, water, and ice often carry these particles great distances.
Sewer system: The drainage conveyance that takes wastewater from home plumbing systems (toilets, showers, sinks, washers, etc) to a sanitary sewer plant.
Source control: Reducing the amount of materials entering the waste stream from a specific source. Action to prevent pollution at its origin. Examples include roofs over oil drums, pallets for liquids, etc.
Storm drain system: A network of conveyance systems that includes roads, gutters, catch basins, grates, underground pipes, streams or open channels designed to transport rain from developed areas and discharged to a receiving body of water. Storm drains can carry a variety of pollutants such as sediments, fecal waste, metals, bacteria, oil, and antifreeze that enter the system through runoff, deliberate dumping, or spills. The City’s storm drain system is also referred to as a Municipal Separate Storm Sewer System (MS4).

Storm Water Management Program Plan (SWMPP): As part of the requirements of the City’s NPDES permit, a Storm Water Management Program Plan (SWMPP) addresses the requirements of the permit with a goal to reduce the discharge of pollutants to and from its MS4 to protect water quality and to satisfy appropriate water quality requirements.  The components of the SWMPP include: Public Education and Outreach; Public Involvement/ Participation; Illicit Discharge Detection and Elimination; Construction Site Runoff Control; Post-Construction Storm Water Management in New Development and Redevelopment; Pollution Prevention/ Good Housekeeping; and Industrial and Commerical Activities Discharge Management Program. 

The latest version of the SWMPP is available here.
Total Maximum Daily Load (TMDL): A numerical quantification of the pollutant loading that can be received by a water body from all sources without exceeding state water quality standards. The TMDL consists of wasteload allocations for point source (e.g., industrial and municipal discharge), load allocations for non-point sources (e.g., agriculture, construction) and a margin of safety so that any additional loading, regardless of source, would not produce a violation of water quality standards. More info here.
Watershed: Geographic area of land from which all runoff drains into a single waterway or the total land area from which rain water drains into a particular stream, drain, or body of water. For example, Makiki, Manoa, and Palolo are the three streams that drain to Mamala Bay, stretching from Diamond Head to Barber's Point along the southern coast of O`ahu, via the Ala Wai Canal.
Wetland: An area possessing three essential characteristics:
(1) Hydrophytic vegetation (or hydrophytes means plants adopted to growing in seasonally or permanently flood condtions),
(2) Hydric soils (soil that is, in its undrained conditions, saturated, flooded, or ponded; and
(3) Wetland hydrology, as defined in the Corps of Engineers Wetlands Delineation Manual. (January 1987). Wetlands also include ponds and mudflats, which while possessing hydric soils and wetland hydrology, may not have the commonly required hydrophytic vegetation. The largest remaining wetland in Hawaii is Kawainui Marsh, Kailua, Oahu. The picture shows Pouhala Marsh, Waipahu, Oahu.