Designing & Constructing a Rain Garden. A Living System for Green Infrastructure

Designing & Constructing a Rain Garden A Living System for Green Infrastructure

Overview Site Selection Design Calculations Planting Design Construction Management Costs Rain Garden D & C: Overview

How do people move through the area? Views (Inside & Out) Noise? Social: Proximity to surrounding environment Site Selection: Site Inventory

Environment: Erosion - Where does it occur? Severity? Slope - Note the steepness and extent of grade changes Exposures - Which way does the slope face? Moisture & Water Issues - Identify water sources: - Roof runoff, drive runoff, slope runoff, low spots - Identify water issues: - Percolation test - Desired:.5 to 1 per hour infiltration rate Sun/Shade = Micro-climate Soil Type -Soil maps or Soil Analysis from Extension office -www.soils.usda.gov/survey/online_surveys/arkansas/ Site Selection: Site Inventory

Environment: Existing Plants 1) Plants to Keep 2) Plants to Relocate 3) Plants to Remove - Unhealthy, exotic, misplaced Heavenly Bamboo Nandina domestica Vs. Yaupon Illex vomitoria Site Selection: Site Inventory

Planting Zones Environment: Site Selection: Site Inventory

Hardscape & Infrastructure: Locate and identify impervious surfaces on property and at times, adjacent to property. - Determine square footage of each Locate all utilities overhead and underground. Site Selection: Site Inventory

Deliverables: Complete Site Inventory Map Slope Analysis Percolation Test Soil test/ Analysis Square Footage of Impervious Surfaces Utilities map Site Selection: Site Inventory

Determine optimal area for rain garden based on: 1. Moisture/water issues 2. How people move through the area and who will see it 3. Other design considerations such as views, wildlife desired, etc. Site Selection: Site Analysis

Guidelines for Placement of a Rain Garden: Place rain gardens at least 10 away from buildings and structures. Allow 25 clearance from septic systems. Avoid soggy areas or areas with high water tables. Consider flatter areas that naturally slope away from structures. Avoid placement within the dripline of trees. Provide adequate space for the rain garden. Site Selection: Guidelines

Sizing a Rain Garden: Rule of Thumb: A typical rain garden should be roughly 1/3 of the impervious area calculated to treat 80-90% of runoff. Ex) 1,200 sq. ft building would require a 400 sq. ft. rain garden. Design Calculations: Bioretention Sizing

Bioretention Sizing: http://www.lid-stormwater.net/bio_sizing.htm Two tools are provided: 1) Infiltration-based sizing The projected reduction in annual stormwater flows due to interception, infiltration, and storage by the bioretention cell can be evaluated for a drainage area. 2) Filtration device calculations Applicable to highly impervious areas where most rainfall becomes runoff and the primary desire is to "biofilter" the runoff. To use the cell sizing tool, you will need to know the: Site's drainage area (acres) Site's area-weighted CN value Proposed cell area (ft 2 ) Proposed cell depth (in) Proposed above-ground ponding depth in the cell (in) Volume fraction of pore space in the cell's fill material (typically 0.2) Design Calculations: LID Tools

Bioretention Sizing: http://www.lid-stormwater.net/bio_sizing.htm Design Calculations: LID Tools

To Determine Depth of Rain Garden: Design Calculations: Depth

Engineering Filter Beds Rain gardens are an infiltration-based storm water management practice that relies on soils with good percolation rates to help manage rainfall to protect water quality. Design Calculations: Soils

The Dirt on Soils The tallgrass prairie ecosystem was dominated by grasses and flowering species (forbs) that had deep root systems. 1) Roots died off and provided organic matter 2) Roots created porous soils More than 90 percent of rainfall would have been absorbed on the landscape. Historically, the hydrologic system was infiltrationbased and groundwater-driven Design Calculations: Soils

What Happens To Soil Functions When We Develop? Compaction Erosion Loss of topsoil Impervious surface Soil organisms Soil structure Natural fertility & Disease prevention Results of Development: Runoff Need for irrigation Biofiltration of pollutants Design Calculations: Soils

Try to make this function like this. Design Calculations: Soils

Soil Strategy Soils investigations are critical to successful rain garden installation. If impounded water in a rain garden does not rapidly drain away, anaerobic conditions can develop which means oxygen is eliminated from pore spaces in the soil profile. Anaerobic conditions will kill beneficial microbes in the soil that help breakdown pollutants and protect water quality. Extended periods of standing water can also kill plants, create odor problems and provides mosquito habitat. Design Calculations: Soils

Design Calculations: Soil Texture & Perc

Soil Amendments If Perc test revealed 1 /hour infiltration and there is at least 5% organic matter in soil, amendments may not be necessary. Design Calculations: Soil Amendments

Soil Amendments: Sand Coarse bank run sand and concrete sand are recommended. Masonry and ball field sand should be avoided. Design Calculations: Soil Amendments

Soil Amendments: Compost Mushroom compost is recommended. Mushroom Compost has high water and nutrient holding capacity and exhibits no nitrogen draw down problems. (Source: http://www.mushroomcompost.org/ ) Design Calculations: Soil Amendments

Soil Amendments: Topsoil A sandy-loam, weed-free topsoil is recommended. Design Calculations: Soil Amendments

Design Calculations: Mulch

With cut and fill, a small berm or dam is built at the lower edge of the rain garden, using material excavated from the upper side of the rain garden. Design Calculations: Berm

Guidelines: 1) Remove and stockpile topsoil. 2) Excavate subsoil and use it as fill material to create a berm on the lower edge of the rain garden. 3) Compact the fill down in 2 inch lifts. 4) Make sure the berm is constructed level across the top. Design Calculations: Berm

Design Calculations: Berm

Deliverables: Size of rain garden Depth of rain garden - Based on slope and soil amendment depth Soil amendment amounts Mulch quantity Design Calculations: Deliverables

3,000 sq. ft building 5% slope Light clay soils: 8 soil amendment 3,000/3 = 1,000 sq. ft rain garden 5% slope = 6 ponding depth Sand = 4 12 yds3 (1.7) = 20 tons Compost = 2 6 yds3 (1.7) = 10 tons Topsoil = 2 6 yds3 (1.7) = 10 tons Mulch = 3 250 ft3 = 9 yds3 Total depth for excavation = 14 Design Calculations: Example

Planting Design Approach 1) Establish preferred design aesthetic. 2) Understand site constraints and conditions. 3) Select appropriate plant species. 4) Prepare planting design plan. Planting Design: Guidelines

Design Plant selection can reflect the type of rain garden desired Butterfly Garden Planting Design: Design Aesthetic

Design Bird Garden Planting Design: Design Aesthetic

Design Low Maintenance Deer Resistant Garden Planting Design: Design Aesthetic

Design Hedgerow Rain Garden for Shaded Areas Planting Design: Design Aesthetic

Site Constraints Planting Design: Constraints

Select Appropriate Species Planting Design: Wetness Zones

Rain Garden: Planting Design Wetland Indicator Status

Select Appropriate Species Hydric Zone Plants: Planting Design: Plant Selection

Select Appropriate Species Mesic Zone Plants: Planting Design: Plant Selection

Select Appropriate Species Xeric Zone Plants: Planting Design: Plant Selection

Planting Design: Native Plant Root Structure

Resources: Lowimpactdevelopment.org BONAP (Biota of North America Program) Plants.usda.gov Planting Design: Plant Selection

Number of Plants Needed: Planting Design: Plant Calculation

Getting Started: Construction: Guidelines

Construction: Curb Cuts Curb Cuts:

10 Steps to Install Rain Garden: Construction: Step 1

10 Steps to Install Rain Garden: Step 4: Prepare Berm if Necessary Construction: Step 4

10 Steps to Install Rain Garden: Step 10: Establish Management Plan Construction: Step 10

Establishment: At time of installation First growing season Second growing season Management: Grow Seasons

Establishment: Recommended: 1 to 2 of water per week Management: Weekly Tasks

Establishment: Management: Weekly Tasks

Inspection: Management: Weekly Tasks

Mulching: Management: Annual Tasks

Pruning: Management: Annual Tasks

Replanting: Remove or replace plant material that did not thrive Management: Annual Tasks

Sediment Management: Management: Annual Tasks

Harvest: Management: Annual Tasks

Inspection: Management: Annual Tasks

Replacement of Materials: Management: Annual Task

Management: Management vs Maintenance

Rain Garden Cost: Average cost: $14/sq. ft. Cost: Materials & Labor

Case Studies: Excavation: In Kind Donation Compost: $113.33 Sand: $113.33 Topsoil: $113.33 Plants: $589.47 Mulch: $206 Cost: Case Study #1

Case Studies: Excavation: $233.90 Compost/Sand/Topsoil: $557.19 pre-mixed Plants: $671.93 Mulch: $40 Cost: Case Study #2

Case Studies: Excavation: $840 In Kind Donation Compost: $270 Sand: $105 Plants: $765 Mulch: $97.31 Cost: Case Study #3

Sources: http://www.bluegrassraingardenalliance.org/files/pdfs/wor king%20with%20rain%20garden%20designers%20and%20 contractors.pdf http://depts.washington.edu/uwbg/docs/stormwater/soilst rategies201.pdf http://www.lowimpactdevelopment.org/raingarden_design/ how2designraingarden.htm ftp://ftp-fc.sc.egov.usda.gov/ia/news/raingardens.pdf www.water.rutgers.org Rain Garden Calculations: Deliverables