Matt Lundsted Principal Comprehensive Environmental Inc.

Transcription

1 Matt Lundsted Principal Comprehensive Environmental Inc.

2 Traditional Development vs. LID Application of LID to New and Redeveloped Sites

3 Standard Engineering Practice Q = CIA Minimum velocity of 3 ft/sec. to transport sand & grit Time of Concentration Control 10, 25 & 100 yr storms Stormwater viewed as a nuisance GOAL: Pipe it to the River

4 Overview Case 1: What if this Recently Constructed Conventional Subdivision Project had met LID Design Standards? Case 2: A Small Residential Subdivision on a Challenging Site Case 3: Redevelopment of a Commercial Retail Site Case 1 Case 2 Case 3 Conclusions

5 Case Study 1 60 lot development central MA Good site plan, but no significant LID features Prepared a theoretical LID scenario No change in roads or layout Used simple techniques to minimize runoff Six main features replaced the conventional drainage and detention system Case 1

6 Good Conventional Development meeting only peak criteria This was built Case 1 Low Impact Development meeting better design criteria This could have been built

7 Design Basis Storm Event 1-inch Volume in cubic feet 17,400 Case 1 Volume in gallons 130,000 2-year 56, , year 89, , year 119, ,000

8 Conventional Detention Basin Case 1

9 LID Features Replace Piping Offsite Case

10 1 Shrub/grass Raingardens OR Drywells Case 1 2 Biofilters or Biocells

11 3 4 Permeable Pavers Case 1 Biofilter or Shrub/Tree Raingarden

12 5 Case 1 Detention Swale / Risers / Checkdams

13 6 Case 1 Naturalized Extended Detention Basin

14 Design Comparison Case 1 System Components Structures Catch basins Manholes Piping 36 inch 18-inch 15-inch 12-inch Conventional , ,350 LID ,400

15 Conventional Design: Construction Cost Estimate Case 1 Manholes $ 72,000 Catch Basins $ 74,000 Piping $ 203,000 Detention Pond $ 101,000 TOTAL $ 450,000 Construction Cost Means 2004

16 LID Design: Construction Cost Estimate Piping $ 47,000 Standpipes $ 3,000 Manholes $ 21,000 Nat.Swales/Basins $ 135,000 Check Dams $ 12,000 Patio/Deck Areas $ 15,000 Bioretention Cells $ 63,000 Rain Gardens $ 102,000 TOTAL $ 398,000 Case 1

17 Summary of Comparison Criteria Conventional LID Case 1 Total Capacity in cubic feet Recharge Area in square feet Recharge Volume in cubic feet Total Cost 114,400 7,100 3,000 $450, ,900 30,500 50,200 $398,000

18 Case Study 2: Small Subdivision on a Challenging Site Challenges Steep slopes Clay soils Road already constructed Design Features Naturalized biofilters with checkdams and micropools Bio-swales for pretreatment Case 2

19 Bio-swales for pretreatment Case 2

20 Naturalized biofilters with checkdams and micropools Case 2

21 LID Design: Construction Cost Estimate Piping $ 1,300 Manholes $ 7,000 Nat.Swales/Basin $ 15,000 TOTAL $ 23,300 Case 2

22 Case Study 3: Commercial Redevelopment Project Roughly 2.5 acre fully paved and impervious mini-mall discharging directly to a water supply brook Case 3 Primary grassed area bordered road so large vegetation/trees not acceptable Some areas of parking lot were underlain by an older parking lot layer

23 Design Features Large biofilter captures much of parking lot runoff Smaller biofilter intercepts and filters another area Pocket raingardens enhance stores Porous asphalt used to infiltrate one area of parking lot; pavers another Leaching catch basins provide pretreatment for other areas Drywells intercept roof leaders Infiltration basin Level spreader using reversed granite curbing taps into existing wetlands Case 3

24 8 Case

25 1 Large biofilter after construction Case 3

26 1 Large biofilter during intense storm Case 3

27 1 Case 3

28 Small biofilter 2 Case 3

29 Pocket raingarden after construction 3 Case 3

30 Pocket raingarden during rainfall 3 Case 3

31 Porous pavers Case 3 4 Case 3 Porous asphalt

32 Leaching catch basins 5 Case 3

33 Drywells for roof leaders 6 Case 3 Case 3

34 Infiltration basin before planting 7 Case 3

35 Level spreader with reverse granite curbing 8 Case 3

36 Case 3

37 Construction Cost Estimate (2005 Bid) Large Biofilter $ 32,250 Small Biofilter $ 4,400 Pocket raingarden (2) $ 13,400 Porous pavers/asphalt $ 15,000 Leaching basins (4) $ 27,000 Roof leaders (13) $ 15,000 Infiltration basin $ 4,000 Vegetated buffer $ 5,200 TOTAL $ 116,250 Case 3

38 Conclusions LID is a change in: Standard Engineering Practice is more than raingardens meets same storm flow criteria meets a higher standard for recharge and retention is cost-effective