“Rivers were here long before man, and for untold ages every stream has periodically exercised its right to expand when carrying more than normal flow. Man’s error has not been the neglect of flood control measures, but his refusal to recognize the right of rivers to their floodplain.” (Engineering News-Record 1937)
Answers to Aerial photo library display questions:
WHEN THE RIVER FLOODS, WHICH SIDE OFTHE RIVER WILL BE MORE DAMAGED, THE OPEN FIELDS or the HOUSES and OFFICES?
The area with houses will experience damage which is more costly than the fields. Flooding can cause not only water damage to a structure, but the structure’s foundation can be undermined, and the soil can become eroded making the structure unsafe. Debris can also enter the house if the flood waters rise rapidly, and the contents of the home can be swept away. Additionally, other property damage can occur such as damage to cars, recreational vehicles, roads, bridges, power lines, and even the sewer system.
When fields flood next to a river, the damage is less costly. Damage can include soil being washed away, loss of vegetation, and loss of the ability to graze until the flood water recedes and the vegetation grows back.
DURING A FLOOD, WHAT TYPES OF POLLUTANTS MAY END UP IN THE RIVER THAT COME FROM THE OPEN FIELDS?
Soil, Trees and branches, Rocks, Manure, Debris from fencing, Pesticides, Herbicides, Fertilizer
HOW ABOUT POLLUTANTS WHICH COME FROM HOUSES AND OFFICES?
Houses can contain pollutants which include:
Pesticides, Herbicides, Fertilizer, Motor Oil, Antifreeze, Transmission fluid, Gasoline, Household chemicals, Rubbing alcohol, Paint, Hydrogen peroxide, Construction debris, Untreated human & pet waste
Offices have most of the previous pollutants and may also have:
Printer toner, Printer ink, Toxic heavy metals from technology waste
WHICH POLLUTANTS DO YOU THINK WILL HAVE MORE IMPACTS ON THE RIVER AND THE SURROUNDING ENVIRONMENT?
The pollutants which have the most impact on the river are those that come from houses and offices. The amount and types of waste found in houses and offices can be poisonous and hazardous to humans and our surrounding environment. These pollutants are not meant to enter the river. The pollutants are harmful to our health and the health of the river and can make us and the animals and plants very sick.
what is a floodplain and why are floodplains important?
A floodplain is the level area bordering a river channel which is likely to be covered with water during a flood. Floodplains are important because the water has a place to spread and be stored when the river overflows its sides (banks). Having a place for the water to spread out reduces the speed of the water which helps to reduce the flood water depths and the flood-related damage downstream. Natural floodplains reduce wind and wave impacts during a storms and floods. The vegetation on an open floodplain protects soil from washing downstream, helps filter the flood waters to improve water quality, and moderates water temperature which reduces impacts to plants and animals. Floodplains also help to recharge groundwater systems and provide essential habitat for many different plants and wildlife, particularly birds. (Azad, 2008)
WHERE ARE THE FLOODPLAINS IN THIS PHOTO?
In this aerial photo, the floodplain is all of the open fields. The area with houses is also located within the river’s floodplain; however, the floodplain in this location has been modified by a levee system to help reduce the potential forflooding. This modification of thefloodplain was done to allow the neighborhood to be built. A levee system is a raised or mounded are along the river bank, put in place to protect the houses, offices and their infrastructure.
Where do you think the water GOES during a flood event?
Floodwaters will spill over the sides (banks) of the river and flow into the open fields. Depending on the amount of flooding, the water could enter the area with houses and offices.
If floodplains are modified and HOUSES, Roads and offices are built (like the area on the east side of the river), Where does the water go Then?
If both sides of the river are built with houses and offices, it is likely that a levee would be put in place along both sides of the river. This will mean during a flood event the river will be forced to flow between the two levees. The river initially will not be able to access the floodplains, which in turn, will increase the speed and depth of the water flow within the main rive channel. The river and flood debris may damage the levee and flow into the area with houses and office, but may also cause further damage downstream.
What would happen downstream?
The increased speed and depth of the river will send more water to downstream areas. This additional volume of water and the potential debris it carries has a more destructive force than if the flood waters were allowed to spread across the open floodplain. Fast, deep water carrying debris can damage structures like houses and offices, but can also damage the river banks. Vegetation such as trees and shrubs can be ripped out. With no roots to hold the soil and rocks in place, whole sections of the river’s banks can be severely damaged. Another community or neighborhood may be downstream and will suffer more costly damage to homes, offices, roads, bridges, and other structures if there are no floodplains to store water and slow the flood. Such structures are at risk from high speed flood flows that can wash away foundations. Structures built in the floodplain can decrease the amount of the floodplain available to store water. This can make flooding worse elsewhere in the valley and downstream. (Lewis and Cobourn) Building in the floodplain reduces the river’s natural ability to limit flood damage. It is less hazardous to prevent development in floodplains than to protect development after it is built. (Lewis and Cobourn)
References:
Lewis, Steve R. and Cobourn,John. Fact Sheet-04-71: River Corridor Protection: Carson River Coalition’s Main Message. 2004. University of Nevada, Reno Cooperative Extension.
Azad, Genie. Carson River Watershed Floodplain Management Plan. 2008. Carson Water Subconservancy District.
Carson River Flooding in Carson Valley (Carson Valley after 1997 Flood)
Photo coutesy of Reno Gazzette Journel
Floodplain Publications
Floodplain Websites
