Green Infrastructure in the Semi-Arid West (U.S. EPA)
Low impact development (LID) is a method of building design and community development with the intention of keeping storm water runoff as uncontaminated as possible. “Slow it down, spread it out, soak it in” is the motto of LID. Slowing the flow of stormwater reduces erosion and flooding dangers. Spreading stormwater out reduces the speed of the stormwater. Allowing the stormwater to soak into the ground recharges underground aquifers and fosters environmental growth.
Green stormwater infrastructure (GSI) is a method of water management that is as sustainable, environmentally friendly, and cost-effective as possible. GSI focuses on creating ecosystems to treat polluted stormwater runoff prior to it entering aquifers, streams, or other waterways. On-site management of stormwater is the first choice, with neighborhood or regional solutions the next preferable solutions.
When LID and GSI are implemented in a semi-arid climate, attention must be paid to our unique environment. With a dry climate and large temperature differences between summer and winter, native plants that are drought tolerant and low maintenance must be chosen that can withstand the harshness of our region.
Glossary of Arid LID Terms
The glossary below was adapted from a booklet that was created by the Arid LID Coalition and published by the Xeriscape Council.
Click here to view the complete booklet: Low Impact Development in a High Desert Climate: Green Stormwater Infrastructure Practices and Case Studies.
The Spanish Colonial word (with Arabic roots) for a community-operated network of irrigation canals typically constructed of earthen berm anchored by tree roots. In addition to the irrigation function of the channels, many cultural practices and historical connections are associated with this infrastructure. Acequias also play an important role in groundwater recharge.
Active Rainwater Harvesting
A method of capturing rainwater from a surface in a container to be redistributed at a later point in time, typically for supplemental irrigation. See cistern.1
An arid climate is one that receives less than 10 inches (25.4 centimeters) of rainfall in a calendar year. Rainfall is sporadic and when it does fall, it is often in the form of a high intensity thunderstorm. Native Plants and animals that survive in an arid climate have adapted to cope with the rare rainfall.1
An earthen depression designed to collect and infiltrate stormwater.9
Raised structure (generally earthen or concrete) constructed to manage direct stormwater runoff and control erosion.9
Best Management Practices (BMPs)
Activities, practices, or prohibitions of practices, designed to prevent or reduce pollution.9
The use of ecological processes incorporating vegetation and organic soils to treat and infiltrate stormwater runoff.3 Usually requires remediating soil compaction and planting carefully chosen xeric plant species that can withstand short periods of saturation. Supplemental irrigation is required for an establishment period. In addition to transpiring and infiltrating significant stormwater volumes, vegetation and healthy soil can enhance pollutant removal from stormwater, improve permeability, and provide ecological and aesthetic value. Examples of bioinfiltration structures include bioswales, raingardens, brown roofs, tree trenches, and contour swales. Also known as bioretention. However, since stormwater is not being retained, the word bioinfiltration more accurately reflects this approach.
See ‘Bioinfiltration,’ which is more accurate for a New Mexico context.
Linear stormwater management features used to convey, slow, and treat stormwater runoff. Bioswales use vegetated and mulched channels that convey stormwater runoff, slow its flow, and enhance infiltration as the water flows down-slope. Often employed to convey runoff from impervious surfaces to localized basins.1
Rooftops designed with xeric or no vegetation for the primary purpose of insulation and gradually releasing stormwater and creating wildlife habitat. Unirrigated except for rainwater.1 See Vegetated Roof.
Bumpout Stormwater Planter
An area for infiltration and green infrastructure interventions created when the curb and gutter is moved out in the portion of the roadway normally reserved for parking This application is effective for highly urbanized areas.8 Otherwise known as ‘bulbouts’ or ‘chicanes’.
Check Dam/ Check Structure
A low, sometimes leaky barrier (such as a gabion) placed perpendicular to the flow of water within a linear drainage feature to slow the water’s flow, allowing more time for infiltration into the soil, and retaining soil and organic matter higher in the watershed.5
A tank that stores rainwater from rooftops or from other impervious areas for later use, thereby reducing the volume of stormwater runoff. Cisterns capture larger proportions of stormwater and address more irrigation demand than rain barrels.2
A depressed linear feature that runs parallel to the contour of a slope to catch stormwater and sediment in place. Typically, contour swales exist in series to capture the overflow from each subsequent swale up slope.
An opening in a curb or a pathway that allows stormwater from the surrounding street catchment area into an area of infiltration, such as a basin. Examples of inlets include curb cuts, curb cores, and sidewalk culverts (aka scuppers).
A basin designed for temporary storage of stormwater to control discharge rates, allow for infiltration, and improve water quality. Outflow structures allow excess water to drain at a reduced flow rate. Must drain within 96 hours per NMSGO / Office of the State Engineer regulation, ordinances may vary.
A gravel-filled hole in the ground that collects stormwater, temporarily storing it and allowing for gradual infiltration. Must be appropriately sized to meet capacity needs. Adaptations of this concept are ‘pumice wicks’ and ‘soil sponges’.1
Anthropocentric term referring to the benefits that humans receive from an ecosystem.
A specific mixing or layering of soil and gravel components to meet desired conditions for infiltration, plant growth, and biological activity.1
The combined measurement of water loss to evaporation and transpiration through the pores of vegetation.5 This measurement is important when determining a water budget.
The initial stormwater runoff captured at the beginning of a rainstorm, not to be confused with the 90th percentile storm. The first flush generally contains a higher pollutant and sediment load compared to the same water volume at later periods of the same storm.9
Wire frames filled with rock that are anchored into slopes, typically along steep slopes or across drainage channels, that aid in retaining soils. Depending on how and where they are used, in time they may become buried in sediment.1
A type of stormwater quality intervention applied to alleys and intended to filter runoff from the alley through the use of permeable pavement.4
Green Stormwater Infrastructure /Green Infrastructure
A term referring to constructed features that leverage the ecological functions of living, natural systems to provide ecosystem services, such as capturing, cleaning, and infiltrating stormwater, creating wildlife habitat, shading and cooling streets and buildings, and calming traffic.3
Green Roof/Vegetated Roof
Although commonly called green roofs, vegetated roofs need not be green year-round and are often planted with drought-tolerant desert plants. While vegetated roofs come in many different forms and types, usually a distinction is made between extensive (no irrigation, minimal use – see ‘Brown Roof’), and intensive (irrigated usable rooftop). In extensive roofs, layers are designed to slow runnoff, absorb water in the soils and vegetation, provide habitat, and also serve as thermal insulation, reducing the temperature fluctuation of the buiding interior. Intensive roofs are designed for human enjoyment and use. It is generally accepted in arid environments that green roofs are not a viable sustainable practice due to the low and infrequent rain events and high evapotransporation rate, requiring significant suplemental irrigation for vegetation.
Heat Island Effect (H.I.E)
This phenomenon describes urban and suburban temperature that are 2° to 10° F warmer than nearby rural areas due to absorbtion and retention of heat by buildings and paved surfaces in the built environment. The HIE can increase energy demands, air conditioning costs, air pollution, greenhouse gas emissions, heat-related illness, and mortality.9
Refers to a material or layer that prevents fluid from passing through.8 Typical examples are roofs, asphalt surfaces, and concrete structures.
The movement of water from the land’s surface into the soil.5
A subsurface hollow chamber that creates space for temporary storage with an open bottom that allows for gradual infiltration of water. Requires permeable soils for infiltration.
A linear excavated area that is lined with filter fabric and filled with rock in order to create additional space for water to collect and infiltrate. Requires permeable soils for infiltration in under 96 hours. May or may not be installed with an underdrain.1
The portion of rainfall that lands on plants and is absorbed or dissipates evaporates.9
Low-Impact Development (L.I.D)
LID is an approach to land development (or re-development) that works with nature to manage stormwater runoff as close to its source as possible. LID employs principles such as preserving and recreating natural landscape features and minimizing effective imperviousness to create functional and appealing site drainage that treats stormwater as a resource rather than a waste product.9 In arid climates, the techniques and applications of LID are different than in other climates
Non-point Source Pollution
Pollution that comes from diffuse sources like auto oil, pet waste, herbicides, and sediment.3 It is picked up by stormwater flowing over roofs, driveways, lawns, and streets, and is carried to streams and rivers.
Passive Rainwater Harvesting
Directing rainwater to swales and basins to benefit adjacent plants. Intended to release water into the soil within 96 hours.1
Refers to anything permitting fluid to pass through.1 Synonym for pervious.
Any paving material that allows stormwater to infiltrate where it falls. Includes permeable interlocking pavers, porous asphalt, and pervious concrete.1
A trench or pit that is backfilled with pumic or scoria, covered with geotextile and mulched with heavy stone. Used to create in-ground reservoirs. The wicks keep the surface relatively dry while collecting rainwater runoff and putting it where plant roots can use it. Pumice or scoria is a good rooting medium for plants but is light and needs a heavy mulch over the top to prevent floating. (Pumice and scoria are both crushed porous volcanic rocks.)1
A shallow depression with native or amended soil and plants that is designed to capture, infiltrate, and filter stormwater from small adjacent contributing areas like rooftops or driveways.10 A type of bioinfiltration structure. Careful attention must be paid to choice of plants that can survive with rainwater only. Requires maintenance.
Required Treatment Volume
Volume of runoff generated by the 90th percentile storm (approximately the first 1/2” of rainfall) required to be detained by the MS4 permit.
Holding stormwater on the surface for more than 96 hours. Retention is legal in NM provided the water infiltrates in less than 96 hours. Not a recommended or legal practice in New Mexico unless water rights are available.1 A basin designed without an outlest, and designed to reatin stormwater runoff and release it only through infiltration or evaporation. These can be used to capture first flush flows, or to meet MS4 Require Treatment Volume criteria. Must drain in less than 96 hours.
Soil, sand, and minerals washed from land into water usually after rain. Excessive sediment can destroy fish nesting areas and animal habitats, clog french drains and porous pavement, and obscure waters so that sunlight does not reach aquatic plants.5 It can also carry non-point source pollution.
A pretreatment area at the inlet to a structural GSI practice used to capture sediment, (these float and won’t be captured in a sediment trap) and other pollutants through settling.9
A climate receiving between 10 and 20 inches of rainfall per year.
Additions to native soils to improve plant growth, water infiltration, and storage.9 By building healthy soil, filtration is also improved.
An innovation on the pumice wick concept, sponges are holes approximately 1’ x 1’ x 2’ deep dug within the rooting area of trees in rainwater harvesting basins and backfilled with a non-floating mix of 5/16” pumice, sand, composted woody materials (around 1”) and high-quality living compost. The sponges absorb and store rainwater and the compost inoculates the surrounding soil with beneficial micro-organisms.12
See ‘Detention Basin’.
Stormwater Buffer/ Filter Strip
An area that separates land from waterways and is designed to filter and capture pollutants from stormwater.9 Best if vegetated. Otherwise known as ‘filter strips’.
Refers to a material or layer that prevents fluid from passing through.8 Typical examples are roofs, asphalt surfaces, and concrete structures.
An engineered material that maintains the structural integrity of paving while also supporting plant growth.1
Suspended Pavement Systems
A general term for any technology that supports the weight of paving or concrete thereby creating void space and eliminating the need for compaction. Structures allow greater soil volumes that are not compacted for greater tree growth, in-place stormwater management, increased infiltration, and minimizing non-point source pollution.1
A small, carefully engineered area designed to capture and infiltrate stormwater for optimal tree growth.1
A continuous, linear tree pit usually in a street / sidewalk setting, linking street trees together below the paving. Allows for a greater volume for tree root growth and can distribute stormwater among multiple trees. Ideally pervious paving is installed above the tree trench.1
A grid of 2-foot-square planting spaces sunken 6-8 inches below the surrounding native soil to capture rainwater and contain it until it seeps into the soil. Developed in pre-historic times by Southwest Native People for agricultural use.1
A watershed is the area of land where all of the water that falls in it and drains off of it goes to a common outlet. Watersheds can be as small as a footprint or large enough to encompass all the land that drains water into the Rio Grande. (USGS)
A habitat or environment containing little moisture.
Commonly mistaken as ‘zeroscape’, xeric or xeriscape reffers to a landscaping technique that utilizes regionally adapted or native plants with low water demand to reduce supplemental watering and overall water use.1
1. Arid LID Collaborative
2. U.S. Environmental Protection Agency. Arid Green Infrastructure for Water Control and Conservation: State of the Science and Research Needs for Arid/Semi-Arid Regions. August 2016. EPA/600/R-16/146. Written by Jennifer Lee and Carolyn Fisher.
3. Green Infrastructure for Desert Communities. The Watershed Management Group, Tucson, 2017
4. Ultra Urban Guide for Green Infrastructure. City and County of Denver Public Works Dept, 2015
5. Lancaster, Brad. Rainwater Harvesting for Drylands and Beyond, Volume 1. Tucson, AZ; Rainsource, 2014
6. Lancaster, Brad. Rainwater Harvesting for Drylands and Beyond, Volume 2. Tucson, AZ; Rainsource, 2014
8. Urban Street Stormwater Guide. National Association of City Transportation Officials, 2017
9. Low Impact Development and Green Infrastructure Guidance manual, Pima County and City of Tuscon, AZ, 2015.
10. Eastern Washington LID guide (https://fortress.wa.gov/ecy/publications/documents/1310036.pdf)
11. San Diego County LID guide (http://www.sandiegocounty.gov/content/dam/sdc/pds/docs/LID_Handbook_2014.pdf)
Jim Brooks (http://soilutions.net)