USDA NRCS Implementation of NOAA Atlas 14. NRCS Work to Implement NOAA Atlas 14

Transcription

1 USDA NRCS Implementation of NOAA Atlas 1 An Equal Opportunity Provider and Employer Annette Humpal, P.E. USDA NRCS Hydraulic Engineer Background: NRCS Work to Implement NOAA Atlas 1 NRCS Priority to work Nationwide to provide consistent methods for analyzing and using Atlas 1 data NRCS National Water Quality and Quantity Team (WQQT) provided assistance to NRCS State Hydraulic Engineers WQQT had done considerable analysis of the previously released Atlas 1 volumes Methods developed from their previous studies were used in WI 1

2 NRCS Work to Implement NOAA Atlas 1 NRCS Implementation of Atlas 1: Analyzed the Atlas 1 data using GIS o Developed Generalized Precipitation Depths by County o Developed NRCS Temporal Storm Distributions Developed precipitation databases by County NRCS Development of Precipitation Depths by County Developed Precipitation Depths by County: Used GIS to analyze the Atlas 1 grid data and develop mean precipitation depths by County and storm frequency Selected Representative Locations for each WI County from the grid data. These were selected such that the Atlas 1 precipitation depths at these (point) representative locations: Equal to the County Mean for the 100-year, 2-hour Event Within -1.0% and +1.9% (within 1 standard deviation) of the County Means for the 1-yr through 50-year, 2 hour events Precipitation Depths for representative County locations were used in NRCS Hydrology Program Databases The intent of the representative locations is to prepare for future GIS capability of NRCS Hydrology programs 2

3 Iron County: TP0:.80 Atlas 1 (Mean):.0 Atlas 1 (Rep. Loc.):.05 Increase (Rep. Loc.): 6.6% TP0 Versus NOAA Atlas 1 Precipitation Depths 10-Yr, 2-Hr Precipitation Depths Percent Change From TP0 to NOAA Atlas 1 (Representative Location) Waupaca County: TP0:.90 Atlas 1 (Mean):.57 Atlas 1 (Rep. Loc.):.60 Decrease (at Rep. Loc.): 7.7% Change in Precipitation Depth From TP0 to NOAA Atlas 1 (Rep. Loc.) 10 Year, 2 hour (Percent) 8.5 to to to to to to to 7.5 TP0 Versus NOAA Atlas 1 Precipitation Depths 100-Yr, 2-Hr Precipitation Depths Percent Change From TP0 to NOAA Atlas 1 (Representative Location) Ashland County: TP0: 5.0 Atlas 1 (Rep. Loc. = Mean): 7.7 Increase 6.5% Shawano County: TP0: 5.0 Atlas 1 (Rep. Loc. = Mean): 5.0 No Change Change in Precipitation Depth From TP0 to NOAA Atlas 1 (Rep. Loc.) 100 Year, 2 hour (Percent) Grant County: TP0: 6.20 NOAA Atlas 1: 7.69 Increase 2.0%

4 TP0 Versus NOAA Atlas 1 Precipitation Depths 100-Yr, 2-Hr Precipitation Depths Percent Change From TP0 to NOAA Atlas 1 (Representative Location) Ashland County: TP0: 5.0 Atlas 1 (Rep. Loc. = Mean): 7.7 Increase 6.5% Shawano County: TP0: 5.0 Atlas 1 (Rep. Loc. = Mean): 5.0 No Change Grant County: TP0: 6.20 NOAA Atlas 1: 7.69 Increase 2.0% Ozaukee County: TP0: 5.0 NOAA Atlas 1: 6.8 Increase 18.1% Development of NRCS Temporal Distributions From their analysis of the previously completed NOAA Atlas 1, Volumes, the NRCS WQQT concluded The NRCS Type II Storm distribution should not be used with NOAA Atlas 1 precipitation depths.

5 Development of NRCS Temporal Distributions The NRCS WQQT developed a procedure Using ArcGIS 10.0 for deriving temporal storm distributions for a wide range of climate conditions (tropical to arctic) which occur in the US. Developed temporal storm distribution Regions for MW and SE US (Atlas 1 Volumes 7 and 8) Based on ratios of the Atlas 1 (25-yr, 1-hr)/(25-yr, 2-hr) precipitation depths NRCS WQQT Storm Distribution Regions - WI 5 Simplifying to follow County Boundaries for use in NRCS Hydrology Computer Programs 2 Tentative Storm Distribution Regions Less Intense ~Type II More Intense 5

6 NRCS WI Storm Distribution Regions - Final Based on the Primary (>50%) Distribution for Each County and Removal of Islands Final Storm Distribution Regions Less Intense More Intense The New NRCS Storm Distributions were Applied by County in the Hydrology Program Precipitation Databases NRCS Temporal Distributions are: Usually 2 hours in Duration applicable to Watersheds with Tc <2 hours Developed by nesting precipitation depths for all durations (5 min through 2 hr) Most intense (5 min) is centered at 12 hrs Intended to be conservative for design purposes Not intended to duplicate actual storm distributions 6

7 NRCS WQQT New Storm Distributions How will the New NRCS Storm Distributions Impact Computed Peak Discharge Values? 7

8 NRCS WQQT New Storm Distributions Impact on Peak Discharge Initial findings Final Storm Distribution Regions Less Intense More Intense NRCS Distribution Dist Dist Change in Peak Discharge Versus for Type II Distribution ~12% Increase ~2% Increase Transitioning to Atlas 1 Data Use NRCS WI Engineers plan to start using NOAA Atlas 1 precipitation data after the current construction season (Fall/Winter 201) Roll-out of NRCS WI Atlas 1 Data includes: Release of National NRCS Hydrology Programs (EFH2, WinTR-55, WinTR-20?) with updated precipitation databases - Online ~Nov/Dec 201 Release of updated NRCS Wisconsin Hydrology (EFH2 and TR55) spreadsheets Online ~Nov 201 Release of NRCS Engineering Field Handbook, Wisconsin Supplement Online ~Nov 201 Google NRCS Wisconsin Hydrology Hydraulics to find NRCS Wisconsin Engineering Hydrology, Hydraulics webpage, or use web address: 8

9 Temporal Distributions For studies to delineate regulatory floodplain limits, WDNR will accept critical duration analyses for peak flow determinations using Atlas 1 precipitation and: The WDNR State distribution, The SEWRPC 2005 distribution for the Southeastern Wisconsin Region, or The new NRCS distributions. WDNR will not accept Atlas 1 precipitation with the NRCS Type II distribution 17 New NOAA Precipitation-Frequency Atlas for Wisconsin Michael G. Hahn, P.E., P.H. SEWRPC Chief Environmental Engineer Annette A. Humpal, P.E. USDA NRCS Wisconsin Hydraulic Engineer annette.humpal@wi.usda.gov 18 9