Storms Statistics for Texas "a small portion of" TxDOT RMC-3 Research Project 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 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. L-moment diagrams 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

Dimension- less Kappa Distribution Frequency Curves Limited spatial differences Flexible Unambiguous Easy to interpret and use "frequency factors"

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.

COUNTY MEAN_08hr_DEPTH 8hr-90th% El Paso in 0.59 in Lubbock.406 in 1.02 in Travis.494 in 1.24 in Hays.564 in 1.42 in Harris.590 in 1.49 in COUNTY MEAN_24hr_DEPTH 24hr-90th% El Paso 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 90th Percentile Storm Depths 2.52 is the 8 hour - 90 percent frequency factor 2.49 is the 24 hour - 90 percent frequency factor

Expected Depth (E[s]) in a BMP MIT < draw-down time E[s] = inches MIT = draw-down time E[s] = 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 2.Lanning-Rush, Asquith, and Slade (1999): USGS 3.Asquith (1999): USGS 4.Asquith and Famiglietti (2000): Journal 5.Al-Asaadi (2002): MS thesis 6.Asquith (2003): PhD diss. 7.Asquith, Bumgarner, Fahlquist (2003): Journal 8.Asquith and Thompson (2003): Proceedings 8.Strand (2003): MS thesis 9.Asquith and Roussel (2003): USGS 10.Asquith, Roussel, Thompson, Cleveland, and Fang (2004): USGS 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.

Dimensionless Exponential Gamma Kappa Distribution Parameter Estimates

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

Triangular Hyetographs Results from NWS hourly data Results from runoff-producing storms in Texas

Atlas of Depth- Duration 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