FloodingHow can we mitigate it’s effects?

Why is flooding a problem?• Settlers in New Zealand commonly chose to

live next to rivers and lakes, as these were a source of fresh water, and the adjacent plains usually had fertile soil. As a consequence, about two-thirds of New Zealanders now live in areas that are naturally prone to flooding.

• Nearly 70% of towns and cities with populations of over 20,000 have river flood problems.

Source: http://www.teara.govt.nz/en/floods/page-6

Why is flooding a problem? Contd.• Human activity has also increased the likelihood of

flooding. Large areas of native forest were cleared by both Māori and European settlers, leading to a more rapid run-off of rain into stream networks, and to erosion that raised the levels of river beds.

• In urban areas, ground that would normally soak up falling rain has been replaced by buildings, footpaths and roads. This leads to surface flooding during heavy rain, and increases the run-off into storm drains, causing higher water levels in local streams.

Source: http://www.teara.govt.nz/en/floods/page-6

Action Flow Chart

What recommendations can we make to mitigate

this vulnerability?Eg build a second road on

higher ground

What cultural phenomena can we identify as being potentially vulnerable?Eg roads, because they

connects the area

What information do we need to know? What details

are relevant?Eg what roads, how long they are, where they go

How can we map these features to illustrate the

issue?Eg measure the length of roads that will be flooded

What can we do about it?

• Under the Resource Management Act 1991, territorial and regional authorities can regulate land use and construction on high-risk flood plains

• We can utilise both short term and long term strategies to help reduce the effects of flooding by making suggestions to the Manawatu District Council

Short Term strategies (for when the flooding hits)

1. Placing sandbags Around important buildings and roads (sacks filled with sand)

2. Evacuate areas under threat3. Close roads

Long Term Strategies (to propose)1. Damming the river and using control gates2. Creating some sort of warning system3. Relocating roads, buildings, and other cultural

phenomenon4. Constructing stop banks x metres high along

the side of the river5. Construct groynes6. Limiting development in specific areas7. Lower the riverbed8. Raise the bridge

1. Damming the river and using control gates

2. Developing a Warning System

3. Relocating roads, buildings, and other cultural phenomenon

4. Constructing Stopbanks along the edge of the river

These are also called Levees

5. Constructing groynes along the edge of the river to catch sediment and slow erosion down

6. Restricting development in flood-prone areas

Netherlands

7. Lowering the Riverbed by digging gravel out of the river channel

8. Raise the height of the bridge

Class Brainstorm - Costs (Social Political Economic eNvironmental)

Bridge and roads (infrastructure)Washed away, supports damaged, banks erodedpeople unable to leave, and no help/supplies can come in. livelihoods are affected. FarmLivestock drown – source of income EVegetation destroyed – plants (food for livestock/source of income) E NDamage to property S E Disruption of livelihood for the farmers/families SLong term effects of siltation and erosion E N SettlementHomes being damaged/destroyed – people don’t have shelter S EPeople’s property gets damaged/destroyed S ELong term effects of water contamination and pollution, clean up costs S E N Power lines damaged – no power and disrupted communication S

Flooding Mitigation Strategies

Advantages and Disadvantages

Alarm system

Description: warning system of biological/technical nature deployed by an individual/group to inform of a future danger.

Disadvantage: 1: it to expensive2: if it need fixing it will cost more.

Advantage: 1: it will last a long time2: it will be loud and clear.

Groynes

Advantage• Slows erosion• Lowers risk of floods• Interesting sight

Disadvantage• Accelerates down drift

erosion• Causes people to assume

places like beaches are not a natural feature

Constructing groynes along the edge of the river to catch sediment and slow erosion down

Groynes are used as water structures that prevent the depositing of sediment and also interrupts water flow so that erosion is reduced. In rivers, Groynes help aid in water navigation and they also help prevent sediment depositing.

DEVELOPING A WARNINGSYSTEM!

My long term strategy for Mitigation strategy is an alarm. At the rivers there will be an alert level. There will be a sensor where the water reaches. Once the water reaches the maximum height of the river the

sensor will go off, triggering the alarm located around the river and warning the local villagers.

An advantage of this warning system is that it will give the villagers time to collect the belongings they need

for their homes and head to higher ground as the alarm will trigger when the river reaches its maximum

height before destruction occurs However this alarm may have its disadvantages. At one point in time a family may have their TV on to loud, they may be out of town to collect personal belongings, the alarms may be dimmed

in sound and also stress may fall upon the villagers and trauma may occur.

Another advantage of this warning system if we are able to allow the sirens to be loud enough, it will alert the whole village which will help the villagers escape from the destruction and

collect important items and be safe and also help the villagers to remain calm and secure about the nearest high ground for their escape.

A disadvantage of this alarm is the sensors may not work due to the water destruction of the river or also that the sensor may have been taken by the river as water eroded the piece of land

these sensors may have been held on. This allows the villagers to find out about the flood by vision and the villagers will have to fight the destruction whilst preparing their most needed

items and family for fast escape

Mitigation Strategy: Damming river and using control gates.

What is Damming the river and control gates?

-A Barrier constructed across a waterway to control the flow or raise of level of water.

Disadvantage; It is a lot of money to build a River Damm which does affect our economy because we are spending a lot of money .Advantage; It protects us from floods which can not only harm our lives, but can kill our plantations in certain areas of country (Farming, etc)

Developing a Warning SystemA Warning system is an alarm system that triggers the sensors if there is a case of Flooding which sends out warning sirens to the people.

Advantages:- Quicker method of

warning the people without having to go out and check yourself

- Gives a very clear warning when sirens go off.

Disadvantages:- Cost a lot of money to

have these systems installed

- Sensors might go off at anytime (kids may just splash water)

Creating some sort of warning system

Description

Some sort of warning system should be created. This could help mitigate flooding as it has a sensor with a restricted level of amount of water that it can consume before it triggers the siren, alarming everyone that there is going to be a flooding occurring.

Advantages

• Everyone is warned that there is going to be a flood and therefore can react quicker.

• People are able to retrieve their belongings needed before any destruction occurs.

• People are able to evacuate their homes before any destruction occurs.

Disadvantages

• Some people may not hear the siren as it may not be loud enough.

• Something could go wrong and the siren is not triggered.

• Someone could tamper would the system creating a false or stopping the alarm from going off.

Groyne

A groyne is a wall or jetty built out from a riverbank or shore to slow down the process of erosion.

Advantages:• They trap sediment

from longshore drift which builds up the beach.

• They last long.Disadvantages:• They starve beaches

further down the coast of sediment.

• They are expensive to build.

What are Groynes?A wall made of either wood, steel, rubble mounds or sand-filled bags which is extended from coastlines to halt longshore drift.

Constructing groynes along the edge of the river to catch sediment and slow erosion

down

Advantages and Disadvantages

Advantages• Slows down erosion• Inexpensive• Doesn’t affect the

environment around it

Disadvantages• Only slows down erosion, it

doesn’t prevent it.• Long term affects• Can only manage floods a

certain height

DAMS & CONTROL GATES.• Dams and control gates could also be known as Floodgates, this flood gate are adjustable

gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They are there to adjust flow rates in sluices and canals, or they may be designed to stop water flow entirely as part of a levee or storm serge system. Since most of these devices operate by controlling the water surface elevation being stored or routed, they are also known as crest gates. In the case of flood bypass systems, floodgates sometimes are also used to lower the water levels in a main river or canal channels by allowing more water to flow into a flood bypass or detention basin when the main river or canal is approaching a flood stage making it an advantage. A disadvantage of having dams / control gates are that it is not cheap. Another disadvantage is that the upstream side of the dam will be permanently flooded.

This technique of using sirens to warn villagers of a flooding risk is activated when the river levels touch a certain height which is measured by a sensor that will activate the alarm

ADVANTAGES:*It can alert the villagers when a flood is possible*It is possibly a good way tio help people evacuate before the flood approaches

DISADVANTAGES:*the sound may not be loud enough to be heard around the entire area*the sensor can have problems and put out false alarms*the wiring system may have defaults as it is underwater