Flood-inundation Maps for the Susquehanna River near Harrisburg, Pennsylvania, 2013 By Mark A. Roland, Stacey M. Underwood, Craig M. Thomas, Jason F. Miller, Benjamin A. Pratt, Laurie G. Hogan, and Patricia A. Wnek Scientific Investigations Report 2014-5046 Abstract: A series of 28 digital flood-inundation maps was developed for an approximate 25-mile reach of the Susquehanna River in the vicinity of Harrisburg, Pennsylvania. The study was selected by the U.S. Army Corps of Engineers (USACE) national Silver Jackets program, which supports interagency teams at the state level to coordinate and collaborate on flood-risk management. This study to produce flood-inundation maps was the result of a collaborative effort between the USACE, National Weather Service (NWS), Susquehanna River Basin Commission (SRBC), The Harrisburg Authority, and the U.S. Geological Survey (USGS). These maps are accessible through Web-mapping applications associated with the NWS, SRBC, and USGS. The maps can be used in conjunction with the real-time stage data from the USGS streamgage 01570500, Susquehanna River at Harrisburg, Pa., and NWS flood-stage forecasts to help guide the general public in taking individual safety precautions and will provide local municipal officials with a tool to efficiently manage emergency flood operations and flood mitigation efforts. The maps were developed using the USACE HEC–RAS and HEC–GeoRAS programs to compute water-surface profiles and to delineate estimated flood-inundation areas for selected stream stages. The maps show estimated flood-inundation areas overlaid on high-resolution, georeferenced, aerial photographs of the study area for stream stages at 1-foot intervals between 11 feet and 37 feet (which include NWS flood categories Action, Flood, Moderate, and Major) and the June 24, 1972, peak-of-record flood event at a stage of 33.27 feet at the Susquehanna River at Harrisburg, Pa., streamgage. DISCLAIMERS: This report, identified as SIR 2014-5046, and associated data have been approved for release and publication by the Director of the U.S. Geological Survey. Although this database has been subjected to rigorous review and is substantially complete, the U.S. Geological Survey reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the U.S. Geological Survey nor the U.S. Government may be held liable for any damages resulting from its authorized or unauthorized use. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other System, or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also contains copyrighted materials as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. Disclaimer for Flood-Inundation Maps: Inundated areas shown should not be used for navigation, regulatory, permitting, or other legal purposes. The members of the Pennsylvania Silver Jackets team, including the USACE, NWS, SRBC, USGS, and The Harrisburg Authority, provide these maps “as is” for a quick reference, emergency planning tool but assume no legal liability or responsibility resulting from the use of this information. Uncertainties and Limitations for Use of Flood-Inundation Maps: Although the flood-inundation maps represent the boundaries of inundated areas with a distinct line, some uncertainty is associated with these maps. The flood boundaries shown were estimated on the basis of water stages/flows at USGS streamgage 01570500. Water-surface elevations along the stream reaches were estimated by using steady-state hydraulic modeling, assuming unobstructed flow, and using discharges and hydrologic conditions anticipated at the streamgage. The hydraulic model reflects the land-cover characteristics and any bridge, dam, levee, or other hydraulic structures present as of the date of the published map. Unique meteorological factors (timing and distribution of precipitation) may cause actual discharges along the modeled reach to vary from those assumed during a flood and lead to deviations in the water-surface elevations and inundation boundaries shown. Additional areas may be flooded as a result of unanticipated backwater from major tributaries along the main stem or localized debris or ice jams, which can be a common occurrence during floods in the winter months. The flood-inundation boundaries depicted on these maps are based on DEMs of varying resolution. Additional uncertainties and limitations pertinent to this study are described elsewhere in this report. The series of flood-inundation maps may be used in conjunction with NWS river forecasts that may have additional uncertainties inherent or factored into NWS forecast procedures. The NWS uses forecast models to estimate the quantity and timing of water flowing through selected stream reaches in the United States. These forecast models (1) estimate the amount of runoff generated by a precipitation or snowmelt event, (2) simulate the movement of floodwater as it proceeds downstream, and (3) predict the flow and stage (and water-surface elevation) for the stream at a given location (AHPS forecast point) throughout the forecast period (every 6 hours and 3 to 5 days out in many locations). For more information on AHPS forecasts, please see http://water.weather.gov/ahps/ pcpn_and_river_forecasting.pdf. CONTENTS: This report consists of a document and 28 on-line maps, each with data files and metadata. Datafiles for inundation layers: A shapefile shows the water-surface inundation extent. All 28 inundation layers associated with USGS streamgage 01570500-Susquehanna River at Harrisburg, PA are contained within the following shapefile, referenced to water-surface stage level. hbg_pa.shp Depth grids for use with ArcGIS show inundation extent and water depth range. The number in the name represents the gridID number and can be cross-referenced with the shapefile (hbg_pa.shp). hbgpa_01 hbgpa_02 hbgpa_03 hbgpa_04 hbgpa_05 hbgpa_06 hbgpa_07 hbgpa_08 hbgpa_09 hbgpa_10 hbgpa_11 hbgpa_12 hbgpa_13 hbgpa_14 hbgpa_15 hbgpa_16 hbgpa_17 hbgpa_18 hbgpa_19 hbgpa_20 hbgpa_21 hbgpa_22 hbgpa_23 hbgpa_24 hbgpa_25 hbgpa_26 hbgpa_27 hbgpa_28 INSTRUCTIONS AND DOCUMENTATION FOR U.S. GEOLOGICAL SURVEY SCIENTIFIC INVESTIGATIONS REPORT 2014-5046 To access the data: The report and data files can be downloaded via the web from http://pubs.usgs.gov/sir/2014/5046/. The main product is a Portable Document Format (.pdf) report which requires Adobe Acrobat for viewing. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com. To access the inundation layers and depth grids, AcrGIS 10.2.2 is preferred, older versions may work also. References to non-U.S. Department of the Interior (DOI) products do not constitute an endorsement by the DOI.