User:Lewguida/new article name here

Sunbury Flood Reduction System is a federally authorized levee built between 1948 to 1952 by the Army Corp of Engineers around the perimeter of Sunbury, Pennsylvania. The flood reduction system provides protection against the Susquehanna River 3 feet below the top of the wall or levee which is 556,000 cubic feet per second. The maximum protection provided by utilizing the remaining three feet, freeboard, will be about 620,000 cfs or 35.80 feet. This height was reached in 1972 during the Hurricane Agnes flood event. Along Shamokin Creek, a freeboard of 3 feet is provided against a discharge of 16,000 cfs occurring when the Susquehanna River is at 556,000 cfs. By utilizing the discharge capacity to the top of the freeboard, Shamokin Creek can discharge about 45 percent more than the design flow with 556,000 cfs in the Susquehanna and can discharge 75 percent more than the design flow during low stages in the Susquehanna River. At the completion of construction the Army Corp transfered fiscal responsibility along with the daily operations and maintenance to the city of Sunbury. In 1993, due to financial constraints the City transfered daily operations and maintenance to the City of Sunbury Municipal Authority.

Concrete Floodwall is constructed where clearance would be too restricted for earthen levee construction. The floodwall is constructed of reinforced concrete on top of steel sheet pile. There are two specific types of concrete floodwall, I-Wall and T-Wall. Each type has several different designs to accommodate different conditions. The "I" type concrete floodwall has an average height of about 11.8 feet above the ground surface and is about 8,060 feet long. The “T” type wall has an average height of 19.2 feet above the ground surface and is about 4,040 feet long. In the event that seepage occurs under the floodwall it will be intercepted by 8 inch perforated pipes called toe-drains which flow to nearby pumping station to be discharged.

Earthen Levee The levees have a crown width of 8 feet and side slopes of 2.5 feet horizontal to 1-foot vertical. The levee along Shamokin Creek has an average height of about 16 feet and the sections of levee along the Susquehanna River and the levee tying into high ground at Mt. Pleasant Road have an average height of about 18 feet. The fill for the levee is impervious material obtained from areas located nearby. Prior to placing the embankment, the entire area under the levee was stripped to a minimum depth of 6 inches, inspection trenches were excavated to determine foundation conditions and, when considered necessary, unsuitable material in the foundation was removed and replaced with impervious fill. In the event that seepage occurs under the levee it will be intercepted by 8 inch perforated pipes called toe-drains which flow to nearby pumping station to be discharged.

Closure structures are openings which were left in levees and walls where it was not practicable, for economic or other reasons, to ramp railroads or highways over the flood protection structures. These openings must be closed during periods of high waters. Aluminum closures, which have a lot of components, are provided at larger openings. Sandbag closures, which are located in the freeboard range and require less frequent installs are provided at smaller openings. These openings must be closed during periods of high waters. There are 6 closure structures of 2 different designs at various locations throughout the system. Number and specific type are: 4 - Aluminum panel (1-vertical and 3-horizontal) 2 - Sandbag

Drainage structures During low river stages all storm drainage from the protected area is discharged by gravity. Overland flow to the levee will be disposed of through culverts. Allowable ponding elevations at the culvert were determined from a detailed topographic survey and field inspections. Each culvert is set low to utilize available head and minimize ponding heights; however, it is set above the stage at which ice might be expected to form in the tail water area. Slopes in the culverts are established so that deposition of solids in the culvert will be minimized.

Pumping Stations 80% of the city is surrounded by levee and floodwall which acts as a perimeter protection against the rising river and creek during a flood. During an event the perimeter protection, while protecting the city from the rising river and creek, now begins to act like a giant bowl collecting rain water internally. Without a natural mechanism to move the collected rain water out of the city, pumps stations are placed throughtout the city to accomplish this task.

Pump stations are situated throughout the system at strategic locations to pump the collected rain water out against the head of both the Susquehanna River and Shamokin Creek.

Capacities range from as little as 3,000 gpm to 113,000 gpm. An example of pumping capacity at the Spring Run station; if the pumps were connected to the Sunbury Community Center swimming pool, it could pump it dry in just 2 minutes!

(( Emergency Preparedness))

Emergency Operations are executed through a comprehensive action plan. The decision to activate all or part of the plan is based on data received from several sources through a monitoring network. The primary source is elevation data received from telemetry stations installed on the Susquehanna River, Spring Run and Shamokin Creek. More particularly a USGS gage located across the river from Sunbury in the Boro of Shamokin Dam. Decisions to implement particular flood fighting operations are condition specific and may vary drastically depending upon the type of event, pre-event conditions, anticipated duration and the magnitude of the event.

References

AgnesFloodwall.jpg

External links

• http://www.usace.army.mil/CEPA/FactSheets/Pages/LeveeTerms.aspx