MAPPING FLOOD STAGES FOR BASIN COMMUNITIES
"The commission may study and determine the nature and extent of
the flood plains of the Susquehanna River and its tributaries. Upon the
basis of the studies, it may delineate areas subject to flooding, including
but not limited to a classification of lands with reference to relative
risk of flooding and the establishment of standards for flood plain use
which will promote economic development and safeguard the public health,
welfare, safety, and property."
--Article 6, Section 6.2 of the Susquehanna River Basin
Compact, P.L. 91-575; 84 Stat. 1509 et seq.
What is a flood stage forecast map?
In the mid-1970s, the Susquehanna River Basin Commission (SRBC) developed
a technique to produce flood stage forecast maps that reflect a range
of stream stages that are tied to forecast points. SRBC prepared and widely
distributed maps for 90 basin communities. Each community map covered
all or portions of that community.
The maps provide details of flood plain areas and flood profiles with
water level contours to show and explain what areas in a community will
be inundated as flood waters reach certain levels (flood stages). These
maps were developed using the flood profiles generated for the federal
flood insurance program and relate to stream gages operated and maintained
by the U.S. Geological Survey. Data from these stream gages are used by
the National Weather Service as forecast points. Each map identifies the
location of the stream gage used in preparing the map.
SRBC currently is seeking funds to produce maps for other communities.
Why are flood stage forecast maps important for the basin?
The Susquehanna River Basin is one of the nation's most flood prone areas--experiencing
over six times the national average in damages per square mile each year.
Of the 1,388 basin communities, 1,150 of those are affected by flooding.
Furthermore, since the year 1810, the basin has been devastated by a major
flood about every 20 years, with the most recent being the January 1996
flash flood.
Because the basin is so flood prone, it is important that community officials
and residents understand what will happen to them when the basin's waterways
reach flood stage. Many basin residents are unfamiliar with and confused
by the term "flood stage." For example, when a flood stage of 20 feet
is predicted, people want to know if that means the water will rise 20
feet from the river's bottom or 20 feet above normal levels. Does it mean
a wall of water 20 feet high will come down the river or that the water
will rise 20 feet over the flood plain?
The flood stage forecast maps convert forecasted flood stages, issued
by the National Weather Service, to mean local water level elevations
for communities within the map study area.
Who uses flood stage forecast maps?
The maps can be used by: 1) emergency personnel to identify areas that
will be inundated first; 2) municipal officials to develop flood evacuation
plans; and 3) individuals living near the flood plain to easily determine
how the forecasted flood will affect them.
How long can the maps be used?
Once produced, the flood stage information is considered permanent. The
only factor that may change is the addition of new development within
the mapped area.
SRBC widely distributed the maps during the early 1980s to the community
officials that were in office then. However, since there is a significant
amount of turnover in local government, it is important that newly-elected
officials be made aware of these maps so the communities can continue
to benefit from them.
How are the flood stage forecast maps used?
Flood stage delineations, indicated by contour lines on the map, are
placed usually in five (5) feet intervals. The intervals are chosen based
on the topography of the flood plain. SRBC determined that a stage interval
of five feet at the forecast point is generally adequate for interpretation
and accuracy.
A flood stage forecast map is used after the National Weather Service
or another reliable source predicts the expected flood stage for a specific
event. Once that information is available, the map user can refer to the
map and follow the instructions included on each map. In the next column
is a sample instruction with the associated graphic.
The delineation lines placed on the map simply define the area of inundation
to be expected if the forecasted flood stage happens to be one of the
pre-selected stage interval lines. If the forecasted stage is not one
that has been placed on the map, the map user must interpolate between
stage interval lines. A more conservative approach, especially where delineations
are provided at less than five feet intervals, is to use the next highest
stage inundation line shown when considering the next course of action.
HOW TO USE THE MAP
1. Locate your property on the map.
2. Determine the flood stage which will affect you. Consider not only
water on your property, but also water preventing your evacuation.
3. Listen for forecasts on the radio and television of stages at the
stream gage used on the map.
4. If the forecasted stage could affect you, begin emergency actions.
If not, listen for revised forecasts until waters recede.
EXAMPLE: If you live in House A, river stages greater than 24 feet [indicated
as 24 on the map] would affect your property directly. If your evacuation
route goes through a low-lying area, emergency action may be required
at a lower stage than the stage affecting your property.
Available Flood Stage Forecast Maps
Maps for areas marked with an * are available from the U.S. Army Corps
of Engineers.
| Municipality
| County
| Coverage
| Reach
|
|
| Full
or Partial
|
|
| Pennsylvania
|
|
|
|
| Allison
Twp.
| Clinton
| P
| Jersey
Shore-Lock Haven
|
| Athens
Boro.
| Bradford
| F
| Athens-Sayre-Susquehanna
River and Chemung River
|
| Athens
Twp.
| Bradford
| F
| Athens-Sayre-Susquehanna
River and Chemung River
|
| Bald
Eagle Twp.
| Clinton
| P
| Jersey
Shore-Lock Haven
|
| Bloomsburg
Town
| Columbia
| F
| Town
of Bloomsburg
|
| Brady
Twp.
| Lycoming
| F
| Turbot
Twp. To Lycoming County
|
| Buffalo
Twp.
| Perry
| P
| Upper
Paxton
|
| Buffalo
Twp.
| Union
| P
| Winfield
to Lewisburg
|
| Burnham
Boro.
| Mifflin
| F
| Lewistown-Juniata/Kischocoquillas
|
| Castania
Twp.
| Clinton
| P
| Jersey
Shore-Lock Haven
|
| Chapman
Twp.
| Clinton
| *
| *
|
| Clinton
Twp.
| Lycoming
| P
| Turbot
Twp. To Lycoming County
|
| Columbia
Boro.
| Lancaster
| F
| Lower
Susquehanna
|
| Cunningham
Twp.
| Luzerne
| P
| Shickshinny
|
| Danville
Boro.
| Montour
| F
| Danville
|
| Delaware
Twp.
| Northumberland
| F
| Turbot
Twp. To Lycoming County
|
| Derry
Twp.
| Dauphin
| F
| Harrisburg-Swatara
Cr. And Backwater
|
| Derry
Twp.
| Mifflin
| F
| Lewistown-Juniata/Kischocoquillas
|
| Duboistown
Boro.
| Lycoming
| *
| *
|
| Duryea
Boro.
| Luzerne
| F
| Wyoming
Valley
|
| East
Buffalo Twp.
| Union
| F
| Winfield
to Lewisburg
|
| East
Chillisquaque Twp.
| Northumberland
| P
| Winfield
to Lewisburg
|
| East
Donegal Twp.
| Lancaster
| P
| Lower
Susquehanna
|
| East
Hanover Twp.
| Dauphin
| F
| Harrisburg-Swatara
Cr.
|
| East
Manchester Twp.
| York
| P
| York-Condorous
Cr.
|
| East
Pennsboro Twp.
| Cumberland
| F
| Twp.
Of East Pennsboro-River and Conodoquinet Cr.
|
| Exeter
Boro.
| Luzerne
| F
| Wyoming
Valley
|
| Fairfield
Twp.
| Lycoming
| *
| *
|
| Fairview
Twp.
| York
| F
| Yellow
Breeches
|
| Flemington
Boro.
| Clinton
| F
| Jersey
Shore-Lock Haven
|
| Forty
Fort Boro.
| Luzerne
| F
| Wyoming
Valley
|
| Gamble
Twp.
| Lycoming
| *
| *
|
| Gregg
Twp.
| Union
| F
| Turbot
Twp. To Lycoming County
|
| Harrisburg
City
| Dauphin
| *
| *
|
| Hellam
Twp.
| York
| P
| Lower
Susquehanna/Long Level Area-York County
|
| Hepburn
Twp.
| Lycoming
| *
| *
|
| Hershey
Village (Derry Twp.)
| Dauphin
| F
| Harrisburg-Swatara
Cr.
|
| Hughesville
Boro.
| Lycoming
| *
| *
|
| Hummelstown
Boro.
| Dauphin
| F
| Harrisburg-Swatara
Cr.
|
| Jenkins
Twp.
| Luzerne
| F
| Wyoming
Valley
|
| Jersey
Shore Boro.
| Lycoming
| *
| *
|
| Kelly
Twp.
| Union
| F
| Winfield
to Lewisburg/Turbot Twp. To Lycoming County
|
| Kingston
Boro.
| Luzerne
| P
| Wyoming
Valley
|
| Leidy
Twp.
| Clinton
| *
| *
|
| Lewis
Twp.
| Lycoming
| *
| *
|
| Lewisburg
Boro.
| Union
| F
| Winfield
to Lewisburg
|
| Lewistown
Boro.
| Mifflin
| F
| Lewistown-Juniata/Kischocoquillas
|
| Lisburn
Village (Lower Allen Twp.)
| Cumberland
| F
| Yellow
Breeches
|
| Liverpool
Boro.
| Perry
| F
| Upper
Paxton
|
| Liverpool
Twp.
| Perry
| F
| Upper
Paxton
|
| Lock
Haven City
| Clinton
| *
| *
|
| Londonderry
Twp.
| Dauphin
| F
| Harrisburg-Swatara
Cr. And Backwater
|
| Long
Level Area
| York
| F
| Long
Level Area-York County
|
| Lower
Allen Twp.
| Cumberland
| F
| Yellow
Breeches
|
| Lower
Augusta Twp.
| Northumberland
| P
| Sunbury
to Selingsgrove
|
| Lower
Mahanoy Twp.
| Northumberland
| P
| Upper
Paxton
|
| Lower
Swatara Twp.
| Dauphin
| F
| Harrisburg-Swatara
Cr. And Backwater
|
| Lower
Windsor Twp.
| York
| P
| Long
Level Area-York County
|
| Loyalsock
Twp.
| Lycoming
| *
| *
|
| Lycoming
Twp.
| Lycoming
| *
| *
|
| Mahoning
Twp.
| Montour
| P
| Danville
|
| Manchester
Twp.
| York
| F
| York-Condorous
Cr.
|
| Marietta
Boro.
| Lancaster
| F
| Lower
Susquehanna
|
| Middletown
Boro.
| Dauphin
| F
| Harrisburg-Swatara
Cr. And Backwater
|
| Mill
Hall Boro.
| Clinton
| F
| Jersey
Shore-Lock Haven
|
| Millersburg
Boro.
| Dauphin
| F
| Upper
Paxton
|
| Milton
Boro.
| Lycoming
| *
| *
|
| Milton
Boro.
| Northumberland
| *
| *
|
| Monoghan
Twp.
| York
| F
| Yellow
Breeches
|
| Monroe
Twp.
| Snyder
| F
| Sunbury
to Selingsgrove
|
| Montgomery
Boro.
| Lycoming
| *
| *
|
| Montoursville
Boro.
| Lycoming
| *
| *
|
| Muncy
Boro.
| Lycoming
| *
| *
|
| Muncy
Creek Twp.
| Lycoming
| *
| *
|
| New
Cumberland Boro.
| Cumberland
| F
| Yellow
Breeches
|
| Newton
Twp.
| Lackawanna
| F
| Wyoming
Valley
|
| North
York Boro.
| York
| F
| York-Condorous
Cr.
|
| Noyes
Twp.
| Clinton
| *
| *
|
| Old
Lycoming Twp.
| Lycoming
| *
| *
|
| Penn
Twp.
| Snyder
| P
| Sunbury
to Selingsgrove
|
| Piatt
Twp.
| Lycoming
| *
| *
|
| Pittston
Boro.
| Luzerne
| F
| Wyoming
Valley
|
| Plains
Twp.
| Luzerne
| F
| Wyoming
Valley
|
| Point
Twp.
| Northumberland
| P
| Winfield
to Lewisburg/Danville
|
| Ransom
Twp.
| Lackawanna
| F
| Wyoming
Valley
|
| Renovo
Boro.
| Clinton
| *
| *
|
| Riverside
Boro.
| Northumberland
| F
| Danville
|
| Royalton
Boro.
| Dauphin
| F
| Harrisburg-Swatara
Cr. And Backwater
|
| Rush
Twp.
| Northumberland
| P
| Danville
|
| Sand
Beach Village
| Dauphin
| F
| Harrisburg-Swatara
Cr.
|
| Sayre
Boro.
| Bradford
| F
| Athens-Sayre-Susquehanna
River and Chemung River
|
| Selingsgrove
Boro.
| Snyder
| F
| Sunbury
to Selingsgrove
|
| Shamokin
Dam Boro.
| Snyder
| F
| Sunbury
to Selingsgrove
|
| Shickshinny
Boro.
| Luzerne
| F
| Shickshinny
|
| South
Hanover Twp.
| Dauphin
| F
| Harrisburg-Swatara
Cr.
|
| South
Renovo Boro.
| Clinton
| *
| *
|
| South
Waverly Boro.
| Bradford
| F
| Athens-Sayre-Susquehanna
River and Chemung River
|
| Spring
Garden Twp.
| York
| P
| York-Condorous
Cr.
|
| Springettsbury
Twp.
| York
| F
| York-Condorous
Cr.
|
| Sunbury
City
| Northumberland
| F
| Sunbury
to Selingsgrove
|
| Swatara
Twp.
| Dauphin
| F
| Harrisburg-Swatara
Cr.
|
| Swoyersville
Boro.
| Luzerne
| F
| Wyoming
Valley
|
| Turbot
Twp.
| Northumberland
| F
| Turbot
Twp. To Lycoming County
|
| Union
Deposit Village
| Dauphin
| F
| Harrisburg-Swatara
Cr.
|
| Union
Twp.
| Union
| P
| Winfield
to Lewisburg
|
| Upper
Allen Twp.
| Cumberland
| F
| Yellow
Breeches
|
| Upper
Augusta Twp.
| Northumberland
| P
| Sunbury
to Selingsgrove
|
| Upper
Fairfield Twp.
| Lycoming
| *
| *
|
| Upper
Paxton Twp.
| Dauphin
| F
| Upper
Paxton
|
| Watsontown
Boro.
| Northumberland
| F
| Turbot
Twp. To Lycoming County
|
| West
Chillisquaque Twp.
| Northumberland
| F
| Winfield
to Lewisburg/Turbot Twp. To Lycoming County
|
| West
Fairview Boro.
| Cumberland
| F
| Twp.
Of East Pennsboro-River and Conodoquinet Cr.
|
| West
Hempfield Twp.
| Lancaster
| F
| Lower
Susquehanna
|
| West
Manchester Twp.
| York
| P
| York-Condorous
Cr.
|
| West
Pittston Boro.
| Luzerne
| F
| Wyoming
Valley
|
| West
Wyoming Boro.
| Luzerne
| F
| Wyoming
Valley
|
| West
York Boro.
| York
| F
| York-Condorous
Cr.
|
| White
Deer
| Union
| F
| Turbot
Twp. To Lycoming County
|
| White
Deer Twp.
| Union
| F
| Turbot
Twp. To Lycoming County
|
| Williamsport
City
| Lycoming
| *
| *
|
| Winfield
| Union
| F
| Winfield
to Lewisburg
|
| Wolf
Twp.
| Lycoming
| *
| *
|
| Wormleysburg
Boro.
| Cumberland
| P
| Twp.
Of East Pennsboro-River
|
| Wrightsville
Boro.
| York
| F
| Lower
Susquehanna/Long Level Area-York County
|
| Wyoming
Boro.
| Luzerne
| F
| Wyoming
Valley
|
| York
City
| York
| F
| York-Condorous
Cr.
|
|
|
|
|
|
Maryland
|
|
|
|
| Havre
de Grace City
| Harford
| F
| Conowingo
Dam to Havre de Grace
|
| Perryville
Town
| Cecil
| F
| Conowingo
Dam to Havre de Grace
|
| Port
Deposit District
| Cecil
| F
| Conowingo
Dam to Havre de Grace
|
| Port
Deposit Town
| Cecil
| F
| Conowingo
Dam to Havre de Grace
|
|
| New
York
|
|
|
|
| Addison
Town
| Steuben
| P
| Addison
|
| Addison
Village
| Steuben
| F
| Addison
|
| Barker
Town
| Broome
| *
| *
|
| Bath
Village
| Steuben
| *
| *
|
| Big
Flats Town
| Chemung
| F
| Big
Flats
|
| Big
Flats Town
| Chemung
| *
| *
|
| Binghamton
City
| Broome
| F
| Binghamton-Susquehanna
River and Chenago River
|
| Campbell
Town
| Steuben
| *
| *
|
| Chemung
Town
| Chemung
| P
| Athens-Sayre-Chemung
River
|
| Chenango
Town
| Chenango
| *
| *
|
| Cohocton
Town
| Steuben
| *
| *
|
| Conklin
Town
| Broome
| *
| *
|
| Dickinson
Town
| Broome
| F
| Binghamton-Chenango
River
|
| Elmira
City
| Chemung
| F
| Newtown
Cr.
|
| Elmira
City
| Chemung
| *
| *
|
| Elmira
Heights Village
| Chemung
| F
| Newtown
Cr.
|
| Elmira
Town
| Chemung
| F
| Newtown
Cr.
|
| Endicott
Village
| Broome
| F
| Binghamton-Susquehanna
River
|
| Erwin
Town
| Steuben
| *
| *
|
| Fenton
Town
| Broome
| *
| *
|
| Greene
Town
| Chenango
| *
| *
|
| Horseheads
Town
| Chemung
| F
| Newtown
Cr.
|
| Horseheads
Village
| Chemung
| F
| Newtown
Cr.
|
| Johnson
City Village
| Broome
| F
| Binghamton-Susquehanna
River
|
| Kirkwood
Town
| Broome
| *
| *
|
| Owego
Village
| Tioga
| F
| Owego
|
| Port
Dickinson Village
| Broome
| F
| Binghamton-Chenango
River
|
| Southport
Town
| Chemung
| *
| *
|
| Union
Town
| Broome
| F
| Binghamton-Susquehanna
River
|
| Vestal
Town
| Broome
| F
| Binghamton-Susquehanna
River
|
|
