1 IDF Curve Revisions Using New Regional Rainfall DataNational Hydraulic Engineering Conference August 9-12, 2016 Rippling Water (Basic) Note: This video template is optimized for Microsoft PowerPoint 2010. In PowerPoint 2007, video elements will play, but any content overlapping the video bars will be covered by the video when in slideshow mode. In PowerPoint 2003, video will not play, but the poster frame of the videos will remain in place as static images. The video: Plays automatically after each slide transition. Is 15 seconds long. Seamlessly loops for infinite playback. To add slides or change layout: To add a new slide, on the Home tab, in the Slides group, click the arrow under New Slide, then click under Motion Background Theme, then select the desired layout. To change the layout of an existing slide, on the Home tab, in the Slides group, click Layout, then select the desired layout. Other animated elements: Any animated element you insert will begin after the slide transition and the background video has started. Layouts with video effects: The “(Green) Title and Content” and “(Purple) Title and Content” layouts are creating by using a color overlay on the video. With the video selected, under Video Tools, on the Format tab, in the Adjust group, select Color and choose Teal, Accent Color 6 Light (third row, seventh option from left) or Periwinkle, Accent Color 5 Light (third row, sixth option from left). presented by David Baker, PE

2 IDF Curve Revisions IDF Curve Data

3 IDF Curve Revisions National Oceanic and Atmospheric AdministrationNOAA Atlas 2 NOAA Atlas 14 update Remaining states (not scheduled)

4 IDF Curve Revisions Our own private Idahohere Ada County

5 IDF Curve Revisions IDF Curve Development in IdahoIdaho – NOAA Atlas 2, Volume 5 published 1973 data ended in 1970 that was 46 years ago! IDF Curves from NOAA Atlas 2 Isopluvials for 6 and 24 hour storms Technical Paper 40 for shorter durations

6 IDF Curve Revisions NOAA TECHNICAL PAPER 40TP-40 published 1961 methodology for short durations

7 IDF Curve Revisions Ada County Highway DistrictAda County Highway District (ACHD) Fun Facts: Est. 1972 Boise, Meridian, Kuna, Eagle, Star, Garden City 2,100 miles of urban streets and rural roads Infiltration is primary stormwater outfall method Ponds Seepage Beds

8 IDF Curve Revisions Ada County Highway DistrictIDF curve use Stormwater conveyance design Detention facility design Retention facility design

9 IDF Curve Revisions ACHD PolicyPolicy changes 0.6 in. retention (24 hr event) - NPDES Infiltration rates F.S. 1 to 2 Use of GSI alternatives

10 ACHD IDF Curve Development Green Stormwater Infrastructure

11 ACHD IDF Curve Development Green Stormwater Infrastructure

12 ACHD IDF Curve Development Policy ChangesDesign Storm changes Conveyance – 100-yr to 25-yr Retention/Detention – 100-yr to 25-yr (with emergency conveyance) Existing facilities appear to be oversized Update IDF Curves

13 IDF Curve Revisions When it rains…Available Data 9 Stations Which are best? Eliminated 3 Record Length Location Applicability L moments test

14 ACHD IDF Curve Development And then there were 6Final Station Selections National Climatic Data Center (NCDC) Global Database FTP site ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/d aily/all/

15 IDF Curve Revisions Number Crunchin’Daily precipitation data from 6 stations Screen data Partition data into homogenous sub-regions Fit probability distributions Software – L-moments package (Hosking 1996)

16 IDF Curve Revisions Old vs. NewPrecipitation comparison 23% to 30% difference Why? no significant trends in data Largest observed event 0.9 in. less than Atlas 2 data sets – fewer/regional statistical models

17 IDF Curve Revisions More Old vs. NewFull 6 station comparison 15 to 24% difference

18 IDF Curve Revisions But what if?Facilities have a design life of 25 years +/- Predict IDF curve for design year Climate change models based on projected change in global greenhouse gas (GHG) emissions published emissions scenarios

19 IDF Curve Revisions Back to the FutureClimate change prediction software: SIMCLIM (CLIMsystems) L-moments results utilized Design Year 2050 3.6 to 10% intensity reduction

20 IDF Curve Revisions IDF Curve OptionACHD selected Option 1 Acceptance of climate change model

21 IDF Curve Revisions Anticipated SavingsInfrastructure Costs right-of-way 13 to 38% reduction in footprint construction maintenance

22 IDF Curve Revisions Questions and CommentsDavid Baker, PE 322 E. Front Street Suite 200 Boise, ID 83702 (office) (cell)