Flooding and Its Control Assoc. Prof. Dr. Tarkan Erdik Department of Civil Engineering, I.T.U

Important notes on flooding It is acknowledged that there is not a linearly correlation between rainfall and flood events (a 100 year rainfall event will not result in a 100 year flood event). It is also commonly assumed that the 10-year rainfall will produce the 10-year flood. However, based on research in UK, 140 years rainfall is expected to generate a 100 year flood. A 500-year flood analysis is required for checking the design of bridge foundations against potential scour failure.

Source: Texas Department of Transportation Hydraulic Design Manual, 2006

Application and limitation of flood estimation methods

Recommended Minimum Stream Gauge Record Lengths Some of the gauging stations have only staff gauges without authomatic data recording device, and thus data is only recorded one or twice a day. This may lead to missing of the flood peaks.

Floods are usually considered in terms of peak runoff or discharge in cubic meters per second (m3/s) and hydrographs as discharge per time. If a flood has a 20 percent chance of being equaled or exceeded each year, over a long period of time, the flood will be equaled or exceeded on an average of once every five years. This is called the return period or recurrence interval (RI).

Up to 5m people in U.K. are at risk from river and coastal flooding Annual average damage estimated at £0.7 bn Recent floods have been more frequent Damage extent exacerbated by: Extensive building on flood plains Alterations to riverine channels Changes in recorded rainfall patterns Changes in land management use Climate change expected to increase flooding

Flood damage extent often exacerbated by: River flooding essentially a natural process that helps shape landscape Flooding generally caused by high rainfall and inability of land to drain water effectively - aggravated further when ground saturated Flooding frequently leads to serious water pollution and epidemiological problems Flood damage extent often exacerbated by: Inadequate flood warning systems Use of crude hydroinformatics tools Inadequately trained model users

INADEQUATE CAPACITY (WITHIN BANKS) BANK EROSION AND SILTING CAUSES OF FLOODS PRECIPITATION INADEQUATE CAPACITY (WITHIN BANKS) BANK EROSION AND SILTING LAND SLIDES TIDAL AND BACK WATER EFFECTS POOR DRAINAGE SNOW MELT AND GLACIAL OUT BURSTS

Commercial properties often badly affected by flooding

Embankment breaches often cause severe damage

Many old bridges throttle flow during floods

Single span modern bridges cause less throttling

FLOOD PLAIN ZONING WATER SUPPLY III III II I II I FACTORY HOSPITAL GOVT. OFFICE POWER HOUSE PARK RESIDENTIAL AREA UNIVERSITY FREQUENT FLOOD FLOOD ONCE IN 25 YEARS NORMAL CHANNEL FLOOD ONCE IN 100 YEARS

FLOOD CONTROL MEASURES There are various river engineering works that are used, either singly or in combination, to provide flood protection and reduce flood damages along river reaches. These are summarized below.

Structural and Nonstructural Measures Structural measures keep the floods away from resources in the floodplain Nonstructural measures keep the resources away from floods in the floodplain

Structural FRM Measures Dams Reservoirs Floodwalls Levees Channels Straightening Clearing and snagging Bridge modifications Conveyance modifications Pumping Channel diversions Beach Nourishment

Structural - Reservoirs Mt. Morris Dam McCook, Ill. FLOOD DAMAGE REDUCTION - Reservoirs This is the McCook Quarry. Part of the Greater Chicago Tunnel and Reservoir Plan, creating a reservoir here and at Thornton helps ease basement flooding for an estimated 170,000 structures. Construction has not yet started. Additional Information -- The McCook project was authorized by Congress in 1988 and involves construction of 10.5 billion gallon reservoir in the McCook Quarry. We’re looking at reservoir alternatives. Local sponsor has submitted alternative reservoir plans which Chicago District is evaluating. Mt. Morris Dam -- In the Great Lakes region, the Mount Morris Dam on the Genesee River, protects the city of Rochester, New York, from flooding. The largest gravity dam east of the Mississippi River, it has prevented nearly $1 billion in flood and erosion damages over the last 46 years. Also shown are the Center Hill Lake, one of our multi-purpose projects in middle Tennessee, located on the Caney Fork River and Yatesville Lake in Kentucky, our newest flood control reservoir. Center Hill Lake, Tenn. Yatesville Lake, Ky.

Structural - Walls & Levees Lock Haven, PA Frankfort, KY FLOOD DAMAGE REDUCTION - Walls and levees We have extensive experience in the design and construction of structural features such as T-walls, I-walls, levees, and closure structures of all kinds. The district presentations will show more detailed examples. The West Columbus project in Columbus Ohio is currently under construction. Frankfort, KY West Columbus

Channel Modification Projects Minnesota River, MN, diversion Martins Fork, KY, diversion River Rouge, MI, channelization Harlan, KY, tunnels LOCAL PROTECTION PROJECTS - SECTION 202 Chronic flooding along the Big Sandy River and Upper Cumberland area, such as this, caused Congress to authorize flood control projects under Section 202 of the Energy and Water Development Act of 1981. Whether the construction of floodwalls, gate closures, pump stations, diversion channels or tunnels, Section 202 is helping us relieve many flooding problems. These projects are exempt from normal B/C cost ratio determinations. Planning and Huntington District will speak further on the 202 program. Additional Information -- Chronic flooding of the Levisa and Tug Forks of the Big Sandy River and Upper Cumberland River, is dramatically illustrated here at Fairview, West Virginia, during the extreme flooding of April 1977. The narrow valleys and steep mountains confine all development to the flood plain.

Beach Nourishment, (Before) Miami/Dade County, FL Beach Nourishment, (After) Miami/Dade County, FL

Nonstructural FRM Measures Elevation Relocation Floodwalls, Levees and Berms Buyout/Acquisition Dry Flood Proofing Wet Flood Proofing Flooding Warning/Preparedness

Elevating on Extended Foundation Walls

Elevating on Fill

Elevation on Piers, Posts, Piles, or Columns

Relocation Process Moving the Structure Evacuate temporary roadway Attach structure to trailer Transport structure to new site

Relocation Process Restoration of Old Site Plan must include a new use for the evacuated floodplain Demolish and remove foundation and pavement Disconnect and remove all utilities Grading and site stabilization

Evacuated floodplain area

Ring wall/levee

Ring wall/levee - closure

Ring wall/levee

Dry Flood Proofing: Methods Waterproof Sealant

Dry Flood Proofing Method: Waterproof Sealant

Flood Control Measures

1 River Improvement River improvement is a measure to increase the flow capacity of the existing river channel and includes widening, dredging/excavation, and dike construction as illustrated below. River Improvement

A dutch dike Coastal flooding Low-lying areas

To attain a large flow capacity, widening of the channel is one of the appropriate measures. However, in urbanized area, implementation may be difficult due to land acquisition problem. Measures to reduce peak discharge at the upper reaches of the urbanized area are therefore considered to be necessary 2 Dam The flood peak discharge is reduced and stored in the reservoir and later released so as to reduce the peak discharge in the downstream. The dam should be situated in a place where large quantity of water will be possibly stored. However, such area is constrained by the topographical and geological conditions of the area

3) Retarding Basin A retarding basin has the same function as a dam. In general, a retarding basin is generally constructed in the middle reach to reduce flood discharge at the downstream reaches.

The Watarase Retarding Basin.

4 Floodway Floodway is aimed at diverting floodwater to the sea, lake or another main river from the existing river by excavating a new manmade waterway, in order to avoid the drastic widening of the existing river or to shorten the extension of improvement

Allocation Procedure in Flood Control Planning In the formulation of a flood control plan, all possible flood control measures/facilities should be explored and evaluated from the engineering, socio-economic and environmental viewpoints so as to select the optimum plan.

Runoff Model for Alternatives runoff basin models for SCS unit hydrograph in HEC-HMS window to obtain the design discharge, Model for Allocation of Design Discharge Model for Design Discharge

Storm surge barriers Design & construction Risk management

New York: Verrazano Barrier Closed Open

Verrazano Narrows Barrier