Estimating Peak-Flow Quantiles for Selected Annual Exceedance Probabilities in Illinois

Over, Thomas; Marti, Mackenzie; O’Shea, Padraic; Sharpe, Jennifer

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https://hdl.handle.net/2142/120604 Copy

Description

Title

Estimating Peak-Flow Quantiles for Selected Annual Exceedance Probabilities in Illinois

Author(s)

• Over, Thomas
• Marti, Mackenzie
• O’Shea, Padraic
• Sharpe, Jennifer

Issue Date

2023-09

Keyword(s)

• Floods
• Peak Discharge
• Regression Analysis
• Reservoirs
• Statistical Analysis
• Streamflow
• Streamgages
• Urbanization
• Watersheds
• Basin Characteristics
• Pearson Type 3 Distribution
• StreamStats

Abstract

This report presents the methods, results, and applications of an updated flood-frequency study for the State of Illinois. This study, which uses data through September 2017, updates two previous studies that used data through 1999 and 2009, respectively. Flood-frequency estimates are used for a variety of land-use planning and infrastructure design purposes, including for the hydraulic design of bridges. The flood frequencies presented are the stream discharges (or quantiles) that are exceeded each year with a given probability, called the annual exceedance probability (AEP). Estimates are provided for eight AEPs: 0.5, 0.2, 0.1, 0.04, 0.02, 0.01, 0.005, and 0.002. The basic data used are the annual maximum discharges (peak flows) at streamgages in and near Illinois and the measurable physical properties (basin characteristics) of the basins upstream from those streamgages. The logarithms of the peak-flow records at qualifying streamgages were fit to the Pearson Type 3 distribution using federally recommended methods, providing one of the two primary products of the study, which is the set of peak-flow quantiles at the streamgages and their uncertainties. The other primary product is sets of equations, determined by least-squares regression, that relate the peak-flow quantiles and the basin characteristics. There is one set of equations for each of Illinois’ seven hydrologic regions, and, for each region, one equation for each AEP. These regional equations allow the estimation of peak-flow quantiles at ungaged locations throughout the state and their uncertainties. A set of illustrative example applications is provided, and tables of all results at all study streamgages and regions are provided in associated data releases. The study results are also being made available in a web application, StreamStats.

Publisher

Illinois Center for Transportation/Illinois Department of Transportation

Has Part

• https://doi.org/10.36501/0197-9191/23-019
• ISSN: 0197-9191

Series/Report Name or Number

FHWA-ICT-23-014

Type of Resource

text

Language

en

Sponsor(s)/Grant Number(s)

IDOT-R27-181

Copyright and License Information

No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161.

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