low impact development strategies and techniques jennifer j. bitting, pe the low impact development center, inc. june 2008

outline hydrologic analysis low impact development (lid) site planning strategies lid best management practice selection

hydrologic analysis lid hydrologic considerations lid hydrologic evaluation steps

hydrologic considerations runoff volume control peak runoff rate control flow frequency/duration control water quality control Q T Runoff Hydrograph Pre- development Post development

hydrologic analysis lid hydrologic considerations lid hydrologic evaluation steps

hydrologic evaluation steps 1.delineate the watershed and microwatershed areas 2.determine design storm 3.define modeling technique to be used 4.evaluate predevelopment conditions (baseline) 5.evaluate site planning benefits 6.evaluate lid practice benefits 7.evaluate supplemental needs

outline hydrologic analysis low impact development (lid) site planning strategies lid best management practice selection

lid site planning strategies define development envelope and protected areas reduce limits of clearing and grading use site fingerprinting use drainage as a design element minimize impervious areas disconnect impervious areas increase flow path length

define development envelope and protected areas

reduce limits of clearing and grading

use site fingerprinting place buildings in areas of poor draining soils save soils that drain well for groundwater recharge

use drainage as a design element Source: “Art for Rain’s Sake,” Landscape Architecture Magazine, September 2006

minimize impervious areas alternative roadway layout narrow road sections reduce sidewalks to one side of the road reduce on-street parking reduce rooftop area design driveways to be: shared narrow short permeable acres of public street acres of public street 35% difference

minimize impervious areas alternative roadway layout narrow road sections reduce sidewalks to one side of the road reduce on-street parking reduce rooftop area design driveways to be: shared narrow short permeable Source: Seattle Public Utilities Sewer_System/Natural_Drainage_Systems/Street_ Edge_Alternatives/SPU_ asp

minimize impervious areas alternative roadway layout narrow road sections reduce sidewalks to one side of the road reduce on-street parking reduce rooftop area design driveways to be: shared narrow short permeable Source: Seattle Public Utilities age_&_Sewer_System/Natural_Drainage_Sy stems/Street_Edge_Alternatives/SPU_ asp

minimize impervious areas alternative roadway layout narrow road sections reduce sidewalks to one side of the road reduce on-street parking reduce rooftop area design driveways to be: shared narrow short permeable Source: Seattle Public Utilities age_&_Sewer_System/Natural_Drainage_Sy stems/Street_Edge_Alternatives/SPU_ asp

minimize impervious areas alternative roadway layout narrow road sections reduce sidewalks to one side of the road reduce on-street parking reduce rooftop area design driveways to be: shared narrow short permeable

disconnect impervious areas disconnecting roof drains and directing flows to vegetated areas directing flows from paved areas to stabilized vegetated areas breaking up flow direction from large paved surfaces encouraging sheet flow through vegetated areas

disconnecting roof drains and directing flows to vegetated areas directing flows from paved areas to stabilized vegetated areas breaking up flow direction from large paved surfaces encouraging sheet flow through vegetated areas disconnect impervious areas

increase flow path length maximize overland sheet flow lengthen flow paths increase vegetation minimize slopes increase surface roughness

increase flow path length maximize overland sheet flow lengthen flow paths increase vegetation minimize slopes increase surface roughness

increase flow path length maximize overland sheet flow lengthen flow paths increase vegetation minimize slopes increase surface roughness

increase flow path length maximize overland sheet flow lengthen flow paths increase vegetation minimize slopes increase surface roughness

outline hydrologic analysis low impact development (lid) site planning strategies lid best management practice selection

lid bmps bioretention filter strips vegetated buffers bioswale/grassed swale rain barrels cisterns green roofs porous pavement

bioretention source: source:

green roofs source: source: extensive intensive

vegetated buffers source:

cistern source:

rain barrel source: source:

bioswale / grassed swale source: source:

porous pavement source: g/lid/militaryS272/porousconcrete.cfm source: source: index.html

vegetated filter strip source:

lid best management practices selection 1.define hydrologic control required. 2.evaluate site constraints. 3.screen for candidate practices. 4.evaluate candidate bmps in various configurations. 5.select preferred configuration and design. 6.supplement with conventional controls, if necessary.

define hydrologic control required runoff volume peak discharge frequency and duration of discharge groundwater recharge requirements water quality goals

evaluate site opportunities and constraints space required soil type slopes depth to groundwater proximity to foundations

select practices technical feasibility economic considerations construction maintenance waste disposal social aspects shade noise reduction environmental impacts air pollution

evaluate bmps in various configurations check the combination of bmps for compliance with hydrologic goals adjust the number and size of the bmps until the hydrologic goals are met

lid best management practice selection 1.define hydrologic control required. 2.evaluate site constraints. 3.screen for candidate practices. 4.evaluate candidate bmps in various configurations. 5.select preferred configuration and design. 6.supplement with conventional controls, if necessary.

three aspects of lid hydrologic analysis lid site planning strategies lid best management practices establishes the goal uses site features to achieve the goal adds additional measures to meet the goal