Storms Statistics for Texas
"a small portion of"
TxDOT RMC-3
Research Project
0-4194
U.S. Geological Survey
Texas Tech University
Lamar University
University of Houston
Presentation by
Dr. William H. Asquith,
USGS, Austin
March 18, 2004
Research Relevance
• TxDOT lets about $3billion/yr in construction contracts.
• TxDOT rule-of-thumb is that 40% of this total or $1.2B/yr
is for drainage control or other handling of water.
• Some drainage control associated with BMPs
• BMP design is influenced by statistics of storms
• There is no comprehensive and single-source framework
for estimating storm statistics in Texas for advanced BMP
design
• Publication of results provides TxDOT with a citable
reference(s) to facilitate codification of storm statistics,
armoring for litigation, and means to influence design
guidance from external agencies.
Statistics of Storms
•
•
•
•
•
eNM, OK, TX
NWS hourly data
155 million values
774 stations
MIT: 6, 8, 12, 18,
24, 48, and 72 hours
• Storm Arrival,
Depth, and Duration
– percentiles
– L-moments
– dist. eq. form
• Hyetographs
– new analysis
• Example Problems
L-moment diagrams
L-moment diagrams are
the state-of-the-art tool
for selection
distributions to model
environmental data.
Distribution L-moments
compared to data
L-moments.
Differences between
distributions are clear
and unambiguous.
1. Kappa (4 parameters)
2. Pearson Type III (3 para.)
3. Gamma (2 parameters)
4. Exponential (2 parameter)
Kappa distribution is MOST ACCURATE.
Kappa
Distribution
Dimensionless
Frequency
Curves
MIT has LIMITED
influence on the curve-so does geographic
location
EASY TO USE
Dimensionless Kappa
Distribution
Frequency
Curves
"frequency factors"
• Limited spatial
differences
• Flexible
• Unambiguous
• Easy to interpret
and use
Comparison of
Exponential,
Gamma, Kappa
Dimensionless
Distributions
of Storm Depth
Exponential used in
analytical BMP
equations.
EPA and others suggest
Gamma.
Kappa most accurate
(cutting-edge) and
throws greater outliers.
Mean Storm
Depth for
8-hour MIT
Large east-to-west grad.
Maps used with
dimensionless
frequency curve to
generate storm depth
distribution.
21 maps provided
Mean Storm
Depth for
24-hour MIT
Maps for Arrival Rate
Maps for Storm Depth
Maps for Storm Duration
(Tables also provided.)
Easy to use, consistent, and
logical with many
administrative subdivisions.
90th Percentile Storm Depths
COUNTY MEAN_08hr_DEPTH
El Paso
0.233 in
Lubbock
.406 in
Travis
.494 in
Hays
.564 in
Harris
.590 in
2.49 is the
24 hour 90 percent
frequency
factor
8hr-90th%
0.59 in
1.02 in
1.24 in
1.42 in
1.49 in
2.52 is the
8 hour 90 percent
frequency
factor
COUNTY MEAN_24hr_DEPTH 24hr-90th%
El Paso
0.275 in
0.68 in
Lubbock
.522 in
1.30 in
Travis
.672 in
1.67 in
Hays
.743 in
1.85 in
Harris
.810 in
2.02 in
Expected Depth (E[s]) in a BMP
MIT < draw-down time
E[s] = 0.0748 inches
MIT = draw-down time
E[s] = 0.0511 inches
In this case, having storm
statistics at the draw-down
time MIT yields a smaller
expected depth and the
calculations are tremendously
easier.
Exponential Distribution of storm arrival, depth, and duration.
THANKS
APPENDIX
Precipitation Related Publications by
the TxDOT Research Program
1.
Asquith (1998): USGS
8.
Strand (2003): MS thesis
2.
Lanning-Rush, Asquith, and
Slade (1999): USGS
9.
Asquith and Roussel (2003):
USGS
3.
Asquith (1999): USGS
4.
Asquith and
Famiglietti (2000): Journal
10. Asquith, Roussel, Thompson,
Cleveland, and Fang (2004):
USGS
5.
Al-Asaadi (2002): MS thesis
6.
Asquith (2003): PhD diss.
7.
Asquith, Bumgarner,
Fahlquist (2003): Journal
8.
Asquith and Thompson (2003):
Proceedings
11. Sether-Williams, Asquith,
Cleveland, Fang, and Thompson
(2004): USGS
12. Asquith, Roussel, Cleveland,
Fang, and Thompson (????):
USGS
Hydrology (Precipitation and
Runoff) Influence Infra$tructure
Sand filtration Best-Management Practice (BMP) behind the
speaker's house in north Austin in Shoal Creek watershed.
Distribution Parameter Estimates
Dimensionless
Exponential
Gamma
Kappa
Countywide Mean Tables
Tables listing countywide mean values for storm arrival rate, depth,
and duration for eNM, OK, and TX are provided.
Countywide tables are convenient as many administrative jurisdictions
are coincident with county boundaries.
Runoff-Producing Storms in Texas
Results from NWS hourly data
Triangular
Hyetographs
Results from runoff-producing
storms in Texas
Atlas of
DepthDuration
Frequency of
Precipitation
in Texas
• 96 maps
• 8 recurrence
intervals
• 12 durations
Atlas of Mean
Interoccurrence
Interval of Daily
Precipitation for
Selected
Rainfall
Thresholds
Interoccurrence interval of
0.25 inches or more of daily precipitation
Synthetic Unit Hydrographs