Low Impact Development Training Module 7: Maintenance Evaluation Neil Weinstein

Sponsors 2 District Department of Transportation U.S. Department of Transportation Federal Highway Administration The Low Impact Development Center, Inc. University of the District of Columbia Funding for this project was provided through a grant from the Federal Highway Administration, U.S. Department of Transportation

Contributors 3 The Low Impact Development Center, Inc. John Shorb Landscaping, Inc. Logo Groundwork Anacostia River, D.C.

Copyright 4 Unless otherwise noted, Low Impact Development Training, funded by DDOT & DDOE, is licensed under a Creative Commons Attribution-NonCommerical- ShareAlike 3.0 Unported License. Content provided by cited entities remains the property of those entities and may not be used without their explicit permission.

Overview The functioning of bioretention can often be evaluated through careful visual inspection Based on Chesapeake Stormwater Network’s visual indicators process 5

Expected Outcomes Be able to visually assess the functioning of bioretention Be able to identify potential issues Be able to recommend appropriate maintenance Be able to spot potentially serious issues requiring in depth investigation 6

Visual Indicators Inlet –Obstructions –Erosion –Structural Integrity –Pretreatment Perimeter –Side slope erosion Bed –Sinking –Sediment caking –Ponding depth –Mulch depth and condition –Trash –Bed erosion Vegetation –Cover –Condition –Maintenance –Invasives Outlet Overflow Underdrain 7

Inlet Obstruction Inlets should be clear of debris and accumulated sediment Inlets can be clogged by accumulating sediment, trash that gets lodged, or overgrowing vegetation 8

Good Condition 9 Photo Courtesy of Seattle Public Utilities

Moderate Accumulated leaves should be removed 10 Photo Courtesy of Seattle Public Utilities

Moderate blockage 11 Sweep or vacuum accumulated sediment Photo Courtesy of the Low Impact Development Center, Inc.

Moderate Remove accumulated sediment. Bag and remove from site to prevent re-release. 12 Photo Courtesy of Emily Ayers

Severely obstructed Remove plants and accumulated soil and debris from inlet 13 Photo Courtesy of Emily Ayers

Severely obstructed 14 Photo Courtesy of the Low Impact Development Center, Inc.

Inlet Erosion Check for evidence of erosion at the inlet Mild erosion may be repaired by replacing mulch and eroded media More severe erosion may require inlet stabilization using river rock or riprap, or the installation of energy dissipating structures 15

Inlet erosion 16 Photo Courtesy of Emily Ayers

Inlet erosion 17 Photo Courtesy of Emily Ayers

Pretreatment If there is pretreatment, does it need to be cleaned out? –Trash –Sediment –Weeds 18

Good condition 19 Photo Courtesy of Seattle Public Utilities

Needs cleaning 20 Photo Courtesy of the Low Impact Development Center, Inc.

Inlet structural integrity Does the inlet structure need repair? –Cracked/broken concrete –Erosion underneath inlet structure 21

Good condition 22 Photo Courtesy of DDOT

Side slope erosion Is there evidence of erosion on side slopes? –Bare spots should be covered with vegetation –Slopes may need to be stabilized –If there is severe erosion, check for erosive flows over side slopes 23

Good condition 24 Photo Courtesy of NC Cooperative Extension, NC State University

Needs stabilization 25 Photo Courtesy of NC Cooperative Extension, NC State University

Ponding Volume Check for uniform ponding volume throughout cell surface Variations in surface elevation can be caused by –Media settling –Uneven or excessive media application –Applying too much mulch –Applying too much rock Check for short-circuiting 26

Uneven 27 Photo Courtesy of the Low Impact Development Center, Inc.

Uniform ponding depth 28 Photo Courtesy of Emily Ayers

Mounding Photo Courtesy of The Low Impact Development Center, Inc.

Short-circuiting 30 Photo Courtesy of Jennifer Bitting

Sinking Filter Bed Irregular depressions forming on surface Could be caused by –Uneven settling of media –Migration of sediment into the underdrain Settling can be counteracted by adding additional media to even out the bed surface Sediment migration may require more intensive investigation and repair 31

Good condition 32 Photo Courtesy of DDOT

Sediment Deposition Mild –Raking to disturb sediment can help –Will often resolve itself over time Severe –May have been caused by accident or extreme event –Sediment will probably need to be removed 33

Good condition 34 Photo Courtesy of Seattle Public Utilities

Mild 35 Photo Courtesy of the Low Impact Development Center, Inc.

Severe 36 Photo Courtesy of the Low Impact Development Center, Inc.

Severe 37 Photo Courtesy of the Low Impact Development Center, Inc.

Standing Water The surface of a bioretention cell should be free from standing water within several hours of the end of a rain storm Potential causes: –Too much clay in the soil medium –Excessive sediment deposition on the surface 38

Standing Water 39 Photo Courtesy of the Low Impact Development Center, Inc.

Saturated Soils 40 Photo Courtesy of Emily Ayers

Ponding Depth Check that ponding depth matches plans Typically should be 6-12” Too high: settling Too low: excessive mulch application 41

Good condition 42 Photo Courtesy of the Low Impact Development Center, Inc.

Drainage Area Photo Courtesy of Larry Coffman Too Deep

Mulch Check depth (typically 2-3”) Check condition 44 Photo Courtesy of the Low Impact Development Center, Inc.

Trash Should be removed 45 Photo Courtesy of the Low Impact Development Center, Inc.

Bed erosion Bed erosion may need to be corrected by dispersing flows 46

Bed erosion 47 Photo Courtesy of The Low Impact Development Center, Inc.

Vegetation Depends on landscaping plan Will change over time as plants grow and fill in 48

Newly planted 49 Photo Courtesy of the Low Impact Development Center, Inc.

Filled in 50 Photo Courtesy of Seattle Public Utilities

Vegetative Cover In general, it’s best if as much of the bed surface is covered with vegetation as possible But, designs dominated by shrubs and trees surrounded by mulch are acceptable Causes: –Erosive flows –Excessive ponding depth –Excessive sediment deposition –Ordinary occasional plant mortality 51

52 Photo Courtesy of Jennifer Bitting

Good 53 Photo Courtesy of the Low Impact Development Center, Inc.

Good 54 Photo Courtesy of the Low Impact Development Center, Inc.

Bare spots 55 Photo Courtesy of the Low Impact Development Center, Inc.

Bare spots 56 Photo Courtesy of the Low Impact Development Center, Inc.

Bare spots 57 Photo Courtesy of the Low Impact Development Center, Inc.

Plant Density Plant Location Photos Courtesy of the Low Impact Development Center, Inc.

Too little cover 59 Photo Courtesy of Emily Ayers

Overgrown 60 Photo Courtesy of Emily Ayers

Overgrown 61 Photo Courtesy of the Low Impact Development Center, Inc.

62 Photo Courtesy of the Low Impact Development Center, Inc.

Invasive plants 63 Purple loosestrife? Photo Courtesy Emily Ayers

Probably not in the planting plan 64 Photo Courtesy of the Low Impact Development Center, Inc.

Check underdrain standpipes Good condition –Underdrains clear, free of water and sediment Cause for concern –Sediment in underdrain –Standing water in underdrain 65

Overflows Check for obstructions 66

Overflow 67 Photo Courtesy of the Low Impact Development Center, Inc.

Overflow 68 Photo Courtesy of the Low Impact Development Center, Inc.

Dealing with severe issues May require involving an engineer Sometimes requires excavation of bioretention cell and replacement of media 69

Severe sedimentation Find and stabilize upstream source of sediment Scrape surface to remove excess sediment In severe cases, some or all of the bioretention media may need to be replaced 70

71 Photo Courtesy of the Low Impact Development Center, Inc.

Severe loss of vegetation Investigate potential causes –Poor estabishment due to lack of irrigation –Vegetation not suited to local conditions Select more suitable plant varieties –Disease and/or pest infestation –Physical damage 72

Open water 73 LIDC

Prolonged standing water Standing water for several days after a storm event May see vegetation replaced by wetland plants (cattails, phragmites, etc.) Could be caused by clogging at the surface, within the soil medium, in a filter cloth, or in the underdrain 74

Test excavation Dig a test pit down to the underdrain look for evidence of clogging at media surface, filter cloth, underdrain Look for evidence of low soil oxygen – mottling, gleying Look for failures of filter cloth, underdrain 75

Irving St Image (DSCN3901) Unapproved Material Substitutions Photos Courtesy of the Low Impact Development Center, Inc.

Anybody got a crane? Photo Courtesy of the Low Impact Development Center, Inc.

Maintenance Evaluation exercises 78

79 Photo Courtesy of the Low Impact Development Center, Inc.

80 Photo Courtesy of Emily Ayers

81 Photo Courtesy of Emily Ayers

82 Photo Courtesy of the Low Impact Development Center, Inc.

Review Before beginning maintenance, inspect the bioretention cell to look for signs of potential problems A thorough maintenance evaluation can detect problems before they become severe 83

Resources Chesapeake Stormwater Network TECHNICAL BULLETIN No. 10. Bioretention Illustrated: A Visual Guide for Constructing, Inspecting, Maintaining and Verifying the Bioretention Practice. ( technical-bulletin-no-10-bioretention- illustrated-a-visual-guide-for-constructing- inspecting-maintaining-and-verifying-the- bioretention-practice/) technical-bulletin-no-10-bioretention- illustrated-a-visual-guide-for-constructing- inspecting-maintaining-and-verifying-the- bioretention-practice/ 84