Natural Hazards

Natural Hazards johncallahan Fri, 06/25/2010 - 09:38

Natural Hazards in Delaware

Natural Hazards in Delaware johncallahan Mon, 07/13/2009 - 14:19
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Natural hazards are those events in the physical environment that present risks to human life or property. The DGS identifies and investigates natural hazards to help understand the earth systems that present the hazards and determine strategies to prepare for or mitigate the risks. We are active in advising emergency management agencies on natural hazards, and are included in the Delaware Emergency Operations Plan as an agency having a vital role in dealing with floods, northeaster/extratropical storms, droughts, earthquakes, sinkholes, and dam failures.

Because of the risk of coastal flooding in southern Delaware, the DGS conducts a program to document the effect of tides and winds on coastal erosion, especially for events with potentially large human impact. One effort as part of this program was a study of historical accounts of the effects of a Category 1 hurricane that swept northward from the Outer Banks of North Carolina, hitting Delaware on October 23, 1878. A storm surge in Delaware Bay raised water levels 6 feet in one hour in some areas, and the highest water levels in the Delaware River at Wilmington were as much as 12 feet above present sea level. More than 100 fatalities were attributed to the hurricane and property damage may have been as much as $150 million in today’s currency. This storm may well be the hurricane of record for the Delaware region and provides a worst-case scenario for a modern hurricane.

Northeasters are a natural hazard that affects Delaware. Northeasters are storms with galeforce or stronger winds from the northeast generated by low-pressure systems offshore the U.S. eastern seaboard. These generate storm waves that can result in significant beach erosion. The duration of the storm is considered a critical factor in the severity of the erosion. Two severe northeasters between January 26 and February 6, 1998 brought tropical storm-force wind gusts to the Delaware coast. They produced the third and fourth highest tides measured at Breakwater Harbor near Lewes, high tides of record at the Coast Guard Station at Indian River Inlet and along Indian River at Rosedale Beach, and 20-ft-high waves at a buoy offshore the Delaware-Maryland state line, which caused some overwash of coastal dunes and localized coastal flooding. Few structures were damaged. In contrast, the severity of these storms is dwarfed by the devastating northeaster of March, 1962. Overwash was pervasive along the entire length of the coast; few sand dunes were left intact and barrier islands were essentially flattened. Most structures adjacent to the beach were damaged. However, tides were comparable for these storms; the 1962 storm had five successive high tides that were well above normal, yet the February 1998 storm had several high tides at similar levels as well as low tides that were higher than those of the 1962 storm. The difference in destruction at similar tide levels suggests that wave conditions may have been more severe in the 1962 storm. Given the extensive development of the coastline since 1962, a storm of similar magnitude would today likely cause damage in the billions of dollars and potentially result in human casualties.

Assessment of storm event risks and response strategies depends, in part, on a sound understanding of hydrology and geology. The coastal regions of southern Delaware are impacted by coastal erosion and flooding during large storms, and the Piedmont of northern Delaware is susceptible to flash flooding during major rain events. The DGS serves on the Delaware Emergency Management Agency’s (DEMA) Emergency Response Task Force for flooding, northeasters, and hurricanes and usually have staff located at the Delaware Emergency Operations Center during storm emergencies. We have recently been involved in the development of the Delaware Environmental Observation System in cooperation with DEMA and the Office of the State Climatologist. As part of this, a Coastal Flood Risk Analysis System has been proposed that will integrate stream-flow and tide-gage data with meteorological information in a network to be used for real-time flood analysis/prediction and emergency planning, response, and recovery operations. Other natural disaster-related activities include the DEMA Northeaster Task Force, the DEMA Technical Assessment Center for Natural Disasters, the DEMA State Hazard Mitigation Team, and advising on development of a statewide Dam Safety Program.

Earthquakes are a natural hazard that occur in northern Delaware and adjacent areas of Pennsylvania, Maryland, and New Jersey. Over 550 earthquakes have been documented within 150 miles of Delaware since 1677, and 69 earthquakes have been documented or suspected in Delaware since 1871. Although Delaware does not face the same degree of earthquake hazard as other, more seismically active parts of the county, FEMA and the USGS in 1997 reclassified Delaware from a low seismic risk to a moderate seismic risk. The largest known event in Delaware occurred in the Wilmington area in 1871 with an intensity of VII (Modified Mercalli Scale). In the memory of many Delawareans is the 1973 earthquake, which was a magnitude 3.8 temblor (Modified Mercalli VVI).

Another hazard studied by the DGS is sinkholes. Geologic mapping in the Hockessin area shows an area underlain by marble and other carbonate bearing rocks that are particularly susceptible to sinkhole formation. At the request of the New Castle County government, DGS staff regularly review consultants’ reports related to proposed construction activities in carbonate areas. We also have visited and educated concerned citizens when sinkholes have appeared on their property. Our input helps guide the development of relevant ordinances related to land-use planning and construction activities in these areas.

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Earthquakes

Earthquakes johncallahan Fri, 06/25/2010 - 09:45

Overview of Earthquakes in Delaware

Overview of Earthquakes in Delaware johncallahan Sat, 06/27/2009 - 00:10
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Every year approximately 3,000,000 earthquakes occur worldwide. Ninety eight percent of them are less than a magnitude 3. Fewer than 20 earthquakes occur each year, on average, that are considered major (magnitude 7.0 – 7.9) or great (magnitude 8 and greater). Between 2000 and 2009, the United States experienced approximately 32,000 earthquakes; six were considered major and occurred in either Alaska or California (http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php#tabl…).

Earthquakes do not occur exclusively in the western United States. Seven events with magnitudes greater than 6.0 have occurred in the central and eastern sections of the United States since 1811 (http://earthquake.usgs.gov/earthquakes/states/historical_mag.php). Of these, four occurred near New Madrid, Missouri between 1811 and 1812, and one occurred in Charleston, South Carolina, in 1886. The largest event in Delaware occurred in 1871 and had an estimated magnitude 4.1. The largest recorded event in Delaware occurred in 1973 and had an estimated magnitude of 3.8.

In 1997, Delaware was reclassified from being a low seismic risk state to being a medium seismic risk state by the U.S. Geological Survey (USGS) and the Federal Emergency Management Agency (FEMA).

The Delaware Geological Survey (DGS) currently operates a network of five seismic stations throughout Delaware. Fifty-eight earthquakes have been documented in Delaware since 1871. Refer to Baxter (2000) and http://www.dgs.udel.edu/datasets/catalog-delaware-earthquakes-spreadshe… for more details about the DGS Seismic Network, Delaware Earthquake Catalog, and for documentation of earthquakes.

An earthquake occurred in Delaware on October 9, 1871, and caused severe property damage. In Wilmington, Delaware's largest city, chimneys toppled, windows broke, and residents were quite bewildered by the unusual event. Lighter damage was sustained in northern Delaware at Newport, New Castle, and in Oxford, Pennsylvania. Earth noises, variously described as "rumbling" and "explosive," accompanied the shock in several areas.

A tremor in March 1879 beneath the Delaware River, not far from Dover, was felt "strongly" in that area according to old seismic records. The records, however, do not describe the "strong" effects.

On May 8, 1906, a shock occurred in Delaware just three weeks after the noted San Francisco earthquake in California. Records state this shock was strong at Seaford, in southwest Delaware, but list no details concerning the event.

Two tremors, both below intensity V, occurred in Delaware, one on the Lower Delaware in December 1937, and one near Wilmington in January 1944.

Parts modified from Earthquake Information Bulletin, May - June 1971, Volume 3, Number 3.

More Information

More information about the frequency, locations, and science of earthquakes can be found in the adjacent pages on this site and in the DGS report: Special Publication 23: Earthquake Basics.

Latitude
39.57
Longitude
-75.65
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Catalog of Delaware Earthquakes Spreadsheet

Catalog of Delaware Earthquakes Spreadsheet rockman Fri, 07/31/2009 - 15:11

The occurrences of earthquakes in northern Delaware and adjacent areas of Pennsylvania, Maryland, and New Jersey are well documented by both historical and instrumental records. Over 550 earthquakes have been documented within 150 miles of Delaware since 1677. One of the earliest known events occurred in 1737 and was felt in Philadelphia and surrounding areas. The largest known event in Delaware occurred in the Wilmington area in 1871 with an intensity of VII (Modified Mercalli Scale). The second largest event occurred in the Delaware area in 1973 (magnitude 3.8 and maximum Modified Mercalli Intensity of V-VI). The epicenter for this event was placed in or near the Delaware River. Sixty-nine earthquakes have been documented or suspected in Delaware since 1871.

Publication Date
Spatial Reference System(s)
NAD83
Web Map Service (WMS) Information
Update Status
As Needed
Primary Data Category
Geology
Preview
Latitude MAX
39.85
Latitude Min
38.40
Longitude Max
-75.80
Longitude Min
-75.00

Earthquake Felt Report

Earthquake Felt Report johncallahan Thu, 07/30/2009 - 10:39
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Did you feel an earthquake? If so, please complete our Earthquake Felt Report below.

Please answer every question to the best of your ability. Either fill in the blanks where called for or check the response that best describes the event. If a particular question does not apply or if you don't know how to respond, simply skip it and go on to the next. You can review and modify answers to all the questions at any time. Feel free to include any additional information in the Additional Comments box at the end of this form.

The Earthquake of August 23, 2011

The Earthquake of August 23, 2011 johncallahan Tue, 08/23/2011 - 22:58
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Delaware and surrounding areas experienced an earthquake event on the afternoon of Tuesday, August 23, 2011. According to the US Geological Survey, a magnitude 5.8 earthquake struck at 1:51 p.m. in central Virginia, in an area referred to as "the Central Virginia Seismic Zone" because of its relatively active earthquake activity for the region. The epicenter was located five miles south-southwest of Mineral, Virginia, with the quake was focused at a depth of 6 km (3.7 miles) below the surface. The Virginia Geological Survey reports that this is the largest Virginia earthquake known in historic times. A few small aftershocks have occurred in the hours afterward. (http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/se082311a.html)

How was this earthquake felt in Delaware?

In Delaware, the earthquake was felt in many locations from northernmost New Castle County to coastal and inland Sussex County. The Delaware Geological Survey website had "felt reports" completed by more than 300 respondents as of 5:00 pm on Aug 23 and over 500 respondents by the evening of Aug 24 (thank you to all of you who replied!). Preliminarily, these responses indicate a Mercalli Intensity of III to IV. The average intensity of building shaking reported by respondents was "moderate." The majority of respondents noted movement or shaking of furniture such as, bookcases, chairs, and computer equipment, some window shaking, and a few overturned items such as picture frames, bottles, and sculptures.

As of 4:00 pm, the US Geological Survey website had received reports from 108 individuals in Delaware with an average intensity reply of 3.3, so between Mercalli III and IV. In the area of central Virginia near the earthquake epicenter, intensities of VII or "Very Strong" were reported, a level strong enough to make standing difficult and to damage poorly built structures. The USGS also received numerous responses from throughout the eastern United States.

How is the strength of an earthquake measured?

The intensity can be gauged using the Mercalli intensity scale, which is characterized by how a quake feels to the observer. A Mercalli intensity of III is considered "Slight." It is felt by people indoors, especially on the upper floors of buildings. A Mercalli intensity of IV is termed "Moderate". It is felt indoors and, by some people, outdoors. Dishes and windows are commonly disturbed and rattle; it may give the sensation of a heavy truck striking a building. These two categories fit most of our reports from Delaware.

The Richter scale measures the energy released by an earthquake. Geophysical sensors called seismometers measure the amount of shaking of the ground at numerous locations; in Delaware, we have five seismic stations that cover all three counties. The August 23 temblor fell in the upper end of the Moderate strength range, between Richter magnitudes 5.0 and 5.9. An interesting fact to remember about the Richter scale – an increase of one number, such as from 5 to 6, means a 10-time increase in the amplitude of shaking and 33-time increase in energy released. This 5.9 event had considerably more energy than the magnitude 3.8 quake that occurred in Delaware in 1973.

Why did this earthquake occur?

The Virginia Geological Survey notes that the earthquake activity in the area is associated with old faults related to movements of the earth’s tectonic plates related to ancient mountain building episodes that were followed by the opening of the Atlantic Ocean about 150 million years ago. The opening of the Atlantic Ocean was accompanied by cracking of the earth's crust, or faulting, along eastern North America. Since the period of this rifting ended, the east coast has been fairly quiet tectonically, in contrast with the tectonically active western coast of the United States. Nevertheless, there are areas that still experience a gradual accumulation of tectonic stress that is occasionally released in the form of an earthquake.

Why did we feel this earthquake in Delaware so far from its central Virginia source?

The geology of the Middle Atlantic region of the east coast favors the travel of earthquake energy for great distances. The earthquake epicenter was located in the Virginia Piedmont, an area underlain by hard basement rocks that predate the opening of the present-day Atlantic Ocean. To the west lie ancient hard rocks of the Appalachian Mountains. To the east, the hard basement rocks are overlain by a blanket of softer sediments that thickens toward the Atlantic Ocean. The hard basement rocks of our region have been in generally the same configuration, with gradual sinking, for the last 150 million years. Earthquake energy can travel well through these hard, cold ancient rocks, in contrast with areas such as California where there is abundant faulting and softer rocks, which absorb the energy more quickly.

The DGS will update this page with additional information, as it becomes available, on the earthquake of August 23, 2011.

Links

Reference(s)

Earthquake intensity map from the US Geological Survey at http://earthquake.usgs.gov/earthquakes/dyfi/events/se/082311a/us/index…

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USGS Real-time Earthquakes Map

USGS Real-time Earthquakes Map johncallahan Mon, 02/15/2010 - 11:02
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The above map shows M1+ earthquakes that occurred in the past 7 days. This data stream is served by the United States Geological Survey. However, the seismic observations are collected from numerous organizations withing the US and around the world. The Delaware Geological Survey is a contributing agency and maintains its own seismic network.

More resources on current earthquake monitoring

DGS Seismic Network

DGS Seismic Network johncallahan Fri, 06/25/2010 - 09:52

Seismic Network Map

Seismic Network Map johncallahan Thu, 07/30/2009 - 11:10
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The DGS maintains its own network of seismometers to detect local earthquake activity. Following an earthquake swarm in 1972, the DGS established its first seismometer station in Newark. The network now consists of five seismic stations spread across the state: three stations in the Newark-Wilmington area, one at the DEMA office in southern New Castle County, and one at the Sussex County Emergency Operations Center. Signals are recorded on paper and captured digitally using Earthworm, a seismic processing system developed by the USGS. These records are shared nationally through participation in the Advanced National Seismic System Network, the Lamont-Doherty Cooperative Seismographic Network, the Northeast U.S. Seismic Network, and the Southeast U.S. Seismic Network. Small local earthquakes and larger earthquakes from other parts of the country and the world are clearly resolved by the network.

Bellevue State Park (BVD) Seismic Station

Bellevue State Park (BVD) Seismic Station johncallahan Tue, 07/28/2009 - 00:49
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The seismometer located at Bellevue State Park is placed on the Brandywine Blue Gneiss. The Brandywine Blue Gneiss is the new name given to the granulite-facies felsic gneisses in the Wilmington Complex. Informally called the “blue rocks,” this unit is a medium- to coarse-grained, lineated (pinstriped), two-pyroxene gneiss with variable quartz content and thin, discontinuous mafic layers, pods, and schlieren. The pinstriping and the massive nature of the rock suggest the rock is intrusive; however, deformation and recrystallization have obscured original igneous features.

The unit appears on the Wilmington North, Wilmington South, and Marcus Hook quadrangles where it underlies the city of Wilmington and its northeastern suburbs.



Seismometer:Mark Products L-4C Short period Vertical
Amplifier: Sprengnether AS-110 Gain 68dB
VCO: TC-10 1700 Hz

Latitude: 39.77472
Longitude: -75.49944
Elevation: 58 meters above sea level

Elevation
58 meters above sea level
Latitude
39.77
Longitude
-75.50
Longitude2
-75.50
geolocation

39.77472, -75.49944

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Brandywine Creek State Park (BWD) Seismic Station

Brandywine Creek State Park (BWD) Seismic Station johncallahan Tue, 07/28/2009 - 00:59
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The seismometer located at Brandywine Creek State Park is positioned on the Wissahickon Formation. The Wissahickon Formation is an extensive sequence of pelitic and psammitic gneisses interlayered with amphibolites. With few exceptions, most of the amphibolite layers are less than 30 feet thick. The rocks have been metamorphosed to upper amphibolite facies and isoclinally folded.

The formation is located within the Wilmington North, Kennett Square, West Grove, Newark West, and Newark East quadrangles.


Seismometer: HS101-A Short period Vertical
Amplifier: Emtel 6243 Gain 36dB
VCO: 2720 Hz

Latitude: 39.79944
Longitude: -75.57667
Elevation: 63 meters above sea level

Elevation
63 meters above sea level
Latitude
39.80
Longitude
-75.58
Longitude2
-75.58
geolocation

39.79944, -75.57667

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Delaware Emergency Management Agency (DEMA) Seismic Station

Delaware Emergency Management Agency (DEMA) Seismic Station johncallahan Tue, 07/28/2009 - 14:23
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The seismometer, located at the Delaware Emergency Management Agency, is located on the Columbia Formation. The Columbia Formation is a fine to coarse, feldspathic quartz sand with varying amounts of gravel. It is primarily a body of glacial outwash sediment deposited in a cold climate during the middle Pleistocene.

Seismometer:Geospace Corp. HS-10 Short period
Amplifier: Emtel 6242 Gain -18dB
VCO: 2380 Hz




Latitude: 39.31871
Longitude: -75.60979
Elevation: 14 meters above sea level

Elevation
14 meters above sea level
Latitude
39.32
Longitude
-75.61
Longitude2
-75.61
geolocation

39.31871, -75.60979

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Sussex County Emergency Operation Center (SCOM) Seismic Station

Sussex County Emergency Operation Center (SCOM) Seismic Station johncallahan Tue, 07/28/2009 - 14:30
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The seismometer, located on the property of the Sussex County Emergency Operation Center, is positioned on the Beaverdam Formation. The Beaverdam Formation is a very coarse sand with beds of fine to medium sand. It is interpreted to be a Pliocene fluvial to estuarine deposit.

Seismometer: Geospace Corp HS-10-1/B Short period Vertical
Amplifier: Emtel 6242 Gain -18dB
VCO: 1020 Hz




Latitude: 38.69567
Longitude: -75.36271
Elevation: 15 meters above sea level

Elevation
15 meters above sea level
Latitude
38.70
Longitude
-75.36
Longitude2
-75.36
geolocation

38.69567, -75.36271

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White Clay Creek State Park (NED) Seismic Station

White Clay Creek State Park (NED) Seismic Station johncallahan Tue, 07/28/2009 - 13:58
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The seismometer, located in White Clay Creek State Park, is positioned on the Wissahickon Formation. The Wissahickon Formation is an extensive sequence of pelitic and psammitic gneisses interlayered with amphibolites. With few exceptions, most of the amphibolite layers are less than 30 feet thick. The rocks have been metamorphosed to upper amphibolite facies and isoclinally folded.

The formation is located within the Wilmington North, Kennett Square, West Grove, Newark West, and Newark East U. S. Geological Survey 7.5-minute quadrangles.

Seismometer:Teledyne Geotech S-13 Short period Vertical
Amplifier: Emtel 6243 Gain 24dB
VCO: 2380 Hz

Latitude: 39.72639
Longitude: -75.73611
Elevation: 90 meters above sea level

Elevation
90 meters above sea level
Latitude
39.73
Longitude
-75.74
Longitude2
-75.74
geolocation

39.72639, -75.73611

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Greenville (GEDE) Seismic Station

Greenville (GEDE) Seismic Station johncallahan Wed, 10/01/2014 - 11:46
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The seismic instruments located at the Greenville, DE location were adopted by DGS from the Earthscope Transportable Array, which consists of a network of 400 high-quality, portable broadband seismometers that are being placed in temporary sites across the United States. DGS adopted two of these Earthscope stations, P60A in Greenville, DE and Q61A in Milford, DE. This program provided an outstanding opportunity for Delaware to enhance its seismic monitoring capabilities in the future, and upgrade current antiquated equipment.

The equipment at this station was installed on 2013-04-28.

For more info, visit the station page at the Array Network Facility.

Instruments:

  • Quanterra Q330 Datalogger
  • Streckeisen STS-2 Broadband Seismometer
  • Setra 278 Microbarometer
  • NCPA Infrasound Microphone
  • MEMS Barometric Pressure Gauge

Latitude: 39.8113
Longitude: -75.6358
Elevation: 110 meters (NAVD88)

Elevation
110 meters (NAVD88)
Latitude
39.81
Longitude
-75.64
Longitude2
-75.64
geolocation

39.8113, -75.6358

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Milford (MIDE) Seismic Station

Milford (MIDE) Seismic Station johncallahan Wed, 10/01/2014 - 12:07
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The seismic instruments located at the Milford, DE location were adopted by DGS from the Earthscope Transportable Array, which consists of a network of 400 high-quality, portable broadband seismometers that are being placed in temporary sites across the United States. DGS adopted two of these Earthscope stations, P60A in Greenville, DE and Q61A in Milford, DE. This program provided an outstanding opportunity for Delaware to enhance its seismic monitoring capabilities in the future, and upgrade current antiquated equipment.

The equipment at this station was installed on 2013-05-28.

For more info, visit the station page at he Array Network Facility.

Instruments:

  • Quanterra Q330 Datalogger
  • Nanometrics Trillium 240 v2 Broadband Seismometer
  • Setra 278 Microbarometer
  • NCPA Infrasound Microphone
  • MEMS Barometric Pressure Gauge

Latitude: 38.8799
Longitude: -75.3256
Elevation: 10 meters (NAVD88)

Elevation
10 meters (NAVD88)
Latitude
38.88
Longitude
-75.33
Longitude2
-75.33
geolocation

38.8799, -75.3256

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Historical DGS Seismographs

Historical DGS Seismographs siteadmin Wed, 03/01/2017 - 11:22

Stream and Tide Gage Data for Hurricane Sandy

Stream and Tide Gage Data for Hurricane Sandy johncallahan Wed, 10/31/2012 - 15:41
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Introduction

Hurricane Sandy was a major storm event for the tidal areas of Delaware. As a part of the mission of the Delaware Geological Survey, we have compiled preliminary Delaware tide and stream-level data for Hurricane Sandy and compared them with previous flooding records. The following tables are the result of the compilation. Please note that these data are preliminary and are subject to change as the data are verified. We have also included some rainfall data to show the rainfall distribution throughout the state related to the storm. These data were provided by the Delaware State Climatologists Office (http://climate.udel.edu/) and were collected as part of the Delaware Environmental Operating System (DEOS, http://www.deos.udel.edu/). The following map shows the location of the stream and tide gages and the DEOS stations used in this report.

DEOS Station Storm Precipitation Total
Claymont, DE 5.21"
Newark (White Clay Creek) 6.05"
New Castle 5.73"
Glasgow 6.80"
Blackbird 8.39"
Dover 9.38"
Georgetown 7.92"
Laurel 8.22"
Rehoboth Beach 10.60"
Indian River Inlet 10.98"
Bethany Beach 7.83"
Rainfall data provided by DEOS.
 

Tidal Flooding

The following table is a summary of the preliminary tidal high water levels produced by Hurricane Sandy. The record high levels prior to Hurricane Sandy, the date of these levels, and the event (storm or hurricane) are shown for comparison. Nine record levels were reached for the tide gages on the Nanticoke River, in the Inland Bays and along the tidal portion of the Delaware River and its tributaries north of the Chesapeake and Delaware Canal. We have also included two NOAA tide gage graphs (at the bottom of this page) from Breakwater Harbor and Reedy Point that show the rise and fall of the tides during the storm. The difference between the predicted tides and the actual tides is the tidal surge that was the result of the storm.

  Hurricane Sandy Prior Record High    
Station Gage Height (ft) Date Timez Gage Height (ft) Date Event Tidal
Datum
Data
Source
Delaware River at Marcus Hook 9.94 10/30/12 3:30 9.76 4/17/11 low pressure system MLLW NOAA
Christina River at Newport ***8.06 10/30/12 2:18 8.07 9/17/99 Floyd NGVD 1929 USGS
Christina River at Wilmington 8.26 10/30/12 2:36 7.71 4/16/11 low pressure system NGVD 1929 USGS
Delaware River at New Castle failed during storm *7.68 5/12/08 Mothers Day Storm NAVD 1988 USGS
Delaware River- Delaware City 9.74 10/30/12 1:54 9.38 4/16/11 low pressure system MLLW NOAA
Reedy Pt.- Mouth of C&D Canal 9.10 10/30/12 1:42 9.23 4/16/11 low pressure system MLLW NOAA
Murderkill River at Frederica 4.84 10/29/12 13:18 5.15 5/12/08 Mothers Day Storm NGVD 1929 USGS
Murderkill River at Bowers 4.79 10/29/12 10:36 8.23y 3/3/94 Northeaster NAVD 1988 USGS
Ship John Shoal 9.42 10/30/12 0:12 9.29 4/16/11 low pressure system MLLW NOAA
Brandywine Shoal Light failed during storm 8.66 8/27/11 Irene MLLW NOAA
Breakwater Harbor at Lewes 8.70 10/29/12 9:36 9.22 3/6/62 March '62 Storm MLLW NOAA
Indian River Inlet **6.51 10/29/12 9:54 **5.86 2/5/98 Northeaster NGVD 1929 USGS
Indian River at Rosedale 6.23 10/29/12 10:48 6.99 2/5/98 Northeaster NGVD 1929 USGS
Rehoboth Bay at Dewey Beach 5.34 10/29/12 22:30 4.45 10/31/99 Halloween Northeaster NGVD 1929 USGS
Jefferson Creek at South Bethany 5.44 10/30/12 0:42 3.52 9/19/03 Isabel NGVD 1929 USGS
Little Assawoman Bay 4.82 10/30/12 0:00 3.13 10/25/05 Wilma NGVD 1929 USGS
Nanticoke River at Sharptown 5.59 10/30/12 4:36 4.11 3/3/94 Northeaster NGVD 1929 USGS
* gage malfunction, reading may be spurious
** data erratic, high winds and waves
*** no data collected between 2:18 and 4:18 EDT during peak tide
y previous tide gage, record for the present gage is 7.8 ft for the Mothers Day storm 5/12/08
9.94 red and bold indicates new record high
z Eastern Daylight Time

Stream Flooding

Although significant rainfall occurred throughout Delaware and in southeastern Pennsylvania, no new record stream levels were recorded. Flood stage was reached on five of the streams in northern Delaware. The levels shown in the following table are typical for a heavy rainfall event. We have also included three USGS hydrographs (at the bottom of this page) from the Brandywine at Wilmington, Red Clay Creek near Stanton, and White Clay Creek near Newark streamgages that show the rising water levels in the streams during the storm. It is possible or even likely that in areas in the Coastal Plain of Delaware where rainfall was the heaviest that small streams and ditches may have had significant flooding but no stream gages are located in these areas to record the event.

USGS Station Hurricane Sandy
Gage Height (ft)
Flood Stage (ft) Record
Gage Height (ft)
Event
Brandywine Crk at Wilm 16.66 16.50 *18.71 Hurricane Irene 2011
Shellpot Creek 5.78 8.00 13.76 Thunderstorm 1989
Red Clay Creek at Woodale >7.45** 7.50 17.62 TS Henri 2003
Red Clay Creek near Stanton 17.00 16.00 25.52 TS Henri 2003
White Clay Creek at Newark 9.84 11.50 17.13 Hurricane Floyd 1999
White Clay Creek near Newark 15.12 13.50 *17.57 Hurricane Floyd 1999
Christina River at Cooch's Bridge 12.35 10.50 13.73 Hurricane Floyd 1999
St. Jones River at Dover 7.70 - 11.72 Hurricane Irene 2011
Nanticoke River at Bridgeville 8.25 - 10.31 1979
* Record gage height at curent gage location
** Highest recorded value before going out of service during the storm

About the gages, stream and tide data

The Delaware Geological Survey (DGS) is actively involved in the monitoring of natural hazards such as stream and tidal flooding that are the result of large storms. The DGS identifies and investigates natural hazards to help understand the earth systems that present the hazards and determine strategies to prepare for or mitigate the risks. We are active in advising both county and state emergency management agencies on natural hazards. The DGS serves on the Delaware Emergency Management Agency’s (DEMA) Emergency Response Task Force for flooding, northeasters, and hurricanes and had staff located at the Delaware Emergency Operations Center during Hurricane Sandy.

An important component of monitoring storm events is having a real-time stream and tide gage network. These gages allow for monitoring of flooding during a storm as it happens to provide information to emergency managers and responders regarding areas of flooding and areas that may be flooded given the trends of rising stream or tide levels. The US Geological Survey, in cooperation with the Delaware Geological Survey, through a Federal-State partnership program operates and maintains stream and tide gages throughout Delaware.

Funding for operation and maintenance of this partnership program is provided by the Delaware Geological Survey, US Geological Survey, Delaware Department of Natural Resources and Environmental Control, Delaware Emergency Management Agency, City of Wilmington, City of Newark, and United Water Delaware.

The National Oceanic and Atmospheric Administration (NOAA) maintains tide gages in the Delaware Bay and River for purposes of navigation safety, environmental stewardship, and environmental assessment and prediction. These gages are an invaluable resource for real-time tidal conditions in the Delaware Bay and River.

Additional Information

Contact Us

For more information on Delaware flooding due to Hurricane Sandy, please contact Kelvin Ramsey at the Delaware Geological Survey (delgeosurvey@udel.edu, 302-831-2833.) For rainfall totals, please contact the Delaware State Climatologist Office.

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