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Hydrology > W11 - Flood management > Flashcards

W11 - Flood management Flashcards

1
Q

Why is important to manage ecosystem services?

A

Resources that ecosystems can provide  difficult to put a value on nature
Framework is useful to ‘monetise’ nature  helpful to put things in perspective for non-geographers

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2
Q

What are some supporting ecosystem services?

A
  • Habitats for animals
  • Water cycling
  • Soil formation
  • Nutrient cycling
  • Primary productivity
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3
Q

What are some provisioning ecosystem services?

A
  • Providing land for farming/irrigation
  • Drinking water
  • Hydropower
  • Trade routes
  • Water for industry
  • Land for building on
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4
Q

What are some cultural ecosystem services?

A
  • Mental health benefits – blue space
  • Tourism – brings money into economy
  • Recreation
  • Education
  • Cultural history
  • Sense of place
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5
Q

What are some regulating ecosystem services?

A
  • Nutrient cycling
  • Flood control
  • Water quality
  • Water quantity
  • Sediment supply
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6
Q

What do the descriptive different colours of water mean?

A

Blue: surface and freshwater, stored in snow, stream, lake, wetland, and subsurface

Green: embedded in the evapotranspiration cycle through vegetation (natural systems, forestry, and agriculture)

Grey: polluted wastewater from urban environments that does not contain a significant faecal burden or industrial contamination (showers, laundry, and kitchen washings)

Black: wastewater in a sanitation context which is likely to contain significant pathogen burden and organic matter (toilets and latrines)

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7
Q

What are the flood risk management strategies acting to reduce the probability of flooding?

A

Hard Engineering
o Maintenance of existing flood defences
o Construction of new flood defences
o Construction of flood control schemes (e.g. storage basins)

Source water management and Natural flood management
o Maximise water storage/flow attenuation capacity of the catchment (land use control – wetlands, forests and increasing infiltration on agricultural land)

Planning and enforcement
o Enforcement when activities of riparian owners are detrimental to flood risk
o Minimise new development on flood plain/high risk areas
o Sustainable urban planning

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8
Q

What are the flood risk management strategies acting to reduce the consequences of flooding?

A

More complete flood risk mapping
o understanding where flooding is likely to occur
o Including pluvial (surface water) flooding

Promoting awareness of flooding
o Operating and improving flood warning systems
o Improving actions of individuals and organisations to minimise consequences
o Providing and improving flood incident management

Promoting resilience and resistance of properties already in flood plain/high risk areas
o 2.4 million properties on floodplain in England!
o Waterproof doors, airbricks etc
o Flood insurance

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9
Q

What are the hydrological factors to consider for flood managers

A

meteorological factors + factors controlling water delivery to channel + channel capacity

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10
Q

What are the traditional engineering approaches to flood risk reduction?

A
  • Focus on fluvial flooding
  • Focus on channel capacity
  • Preventing the likelihood of flooding (e.g. over-banking).

Hard engineering approach to water and channel management
o Focus on flooding at problem locations – doesn’t tackle issue of flooding at source
o Embankments – disturbs and churns the environment
o Flood relief channels
o Move water through the system faster.

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11
Q

Infrastructure to redirect/store flow:

A

New Danube, Vienna (Bruce, 2019; Hurby, 2021)
Designed to 1-in-10,000 year event
* Success story in terms of hard engineering approaches
* Entirely man-made channel that runs about 25km through Vienna
* The new Danube is basically cut off from the main Danube for most of the year – become part of the city
* Able to direct all of the extra water and sediment to the extra channel
* Would have been very expensive but has been built to last

Salford flood storage basin
Cost £10 million
Building a bunch of levies that allow for low quality land to be flooded – prevents water from reaching high value areas

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12
Q

Infrastructure to limit flow

A

Thames Barrier
* Designed in the 1970s to withstand what they thought a 1-in-1,000 year flood was to 2030
* Cost £534 million (>£1.6 billion today)
* Operational from 1982
* Should operate to 2060-70 – their climate change and sea level rise predictions were more intense than they were
* Thames Estuary 2100 team already planning replacement
* All of the hard engineering approaches have knock on effects in other places

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13
Q

Keswick hard engineering example:

A
  • Glass flood defence wall
  • But what if the event magnitude exceeds the 1 in 100 year event?
  • Flood defences failed
  • December 2015
  • £2m just to save the pencil museum
  • Massive £6m investment of the wall becomes useless and needs maintaining pretty fast
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14
Q

Dredging to increase channel capacity?

A
  • Limited evidence that dredging is that effective as a flood control
  • Rivers are very good at self-regulating
  • Cost ~£12 per m3 so process vary from £10,000 to > £2 million depending on scale
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15
Q

Challenges to hard engineering options

A
  • How do you decide which defences to prioritise?
  • Increased awareness of need to manage whole catchments (spatial interactions)
  • Growing appreciation that flooding systems are dynamic over time and flood risks increasing (e.g. climate change)
    o We can’t all have massive defences
  • Can we really stop flooding happening?
    o Management rather than elimination?
  • But what are ‘acceptable risks’ from flooding?
  • How land is used
    o Loss of local land – parks dug up to make flood defences
    o Die off of marine life at the River Tees due to dredging higher upstream
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16
Q

What is Soft Engineering, Working With Natural Processes (WWNP) and Natural Flood Management (NFM)

A
  • Managing flood risk by protecting, restoring and emulating the natural regulating function of catchments and rivers
  • Has the potential to provide environmentally sensitive approaches to minimising flood risk, to reduce flood risk in areas where hard flood defences are not feasible
    o Maybe a village too small etc.
  • increase the lifespan of existing flood defences.
  • Working with nature to reduce flood risk
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17
Q

What are the Environment Agency 2018 ‘Working with Natural Processes’ report Categories of NFM Intervention?

A
  • River and floodplain management
  • Woodland management
  • Run-off management
  • Coast and estuarine management
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18
Q

The basis for NFM

A
  • Human activities have altered the hydrological function of most river basins to reduce natural attenuation of flood waves
  • It is possible to restore the basin to a more naturally functioning hydrological system
  • There are also natural kinds of infrastructure (e.g. woody debris dams, bunds) that can be used as an alternative to hard engineering solutions
    (Lane, 2017)
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19
Q

What are NFM Interventions trying to achieve? (Lane 2017)

A
  • Been around for around 10-15 years
  • Said that it worked  people began to make their own defences
  • Hydrograph attenuation
    o Increase upstream storage during extreme events
    o Manipulation of hillslopes to reduce rapid runoff
    o Increase attenuation within channels and the drainage network
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20
Q

Types of river and floodplain management:

A

River restoration: reinstatement of natural processes and features in a river
Floodplain restoration: Restoration of the hydrological connection between rivers and floodplains
Leaky/woody barriers: pieces of wood installed in channel, river corridor or floodplain to manage water
Offline storage areas: areas of floodplain adapted to retain water in a managed way

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21
Q

Types of river restoration:

A

Embankment removal
Re-meandering
Deculverting

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22
Q

Types of floodplain restoration:

A

Beaver reintroduction
Offline storage
Improving floodplain connectivity

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23
Q

purpose of Leaky/woody barriers

A

slows the flow, sediment traps

24
Q

types of runoff management

A

Soil and land: soil aeration, arable systems, grassland systems, hedges and buffer strips
Headwater drainage: hedgewater management, peatland restoration
Runoff pathway: ponds, swales, sediment traps

25
Q

types of headwater drainage:

A

Farming community engagement
Blanket bog restoration
Blocking drainage ditches

26
Q

types of runoff pathways:

A

Leaky barriers on hillslopes
runoff storage ponds
Bit off offline storage
Increases carrying capacity

27
Q

Types of woodland management:

A

Catchment woodland: total area of all woodland within a catchment
Cross-slope woodland: smaller belts of woodland across hill slopes
Floodplain woodland: land within the fluvial floodplain, subject to regular flooding
Riparian woodland: land adjoining a river channel, usually narrow e.g. <5m on either side

28
Q

Purpose of woodland management:

A

Reduce generation and conveyance of flood flows by the water use by trees
Increased soil infiltration beneath woodland
Increased hydraulic roughness exerted by woodland
Reduce soil erosion and sediment delivery

29
Q

Does NFM work? +ves/-ves

A
  • Excellent on the different approaches tried, and the different types of interventions
  • Lots of case studies
  • Uses a very useful ‘what we know/don’t know’ framework

BUT
* Dominated by small scale studies
* Place specific
* Scientific evidence of variable quality
* Highlighted more knowledge gaps than were filled in
* Focussed on loads of small studies that might not be applicable to other areas – how to scale up

30
Q

What is the scientific evidence base for NFM?

A

Dadson et al. (2017)
* NFM can work in small catchments (<20km2)
* Not yet demonstrated for large catchments
* NFM can be effective for smaller floods
* Contribution of NFM to extreme (large) events is uncertain
* But implication that many small interventions could combine to produce large benefits
* There are some key challenges to demonstrating success of NFM
* There are so many different confounding factors that it’s hard to see differences

31
Q

Difficulties in evidencing NFM at large scales

A

Scaling up is difficult because:
o It is hard to experimentally manipulate large catchments
o Lots of confounding variables/changes

Most studies sample before-after, so influenced by synoptic meteorology

Short duration of many studies precludes capture of large events

Many studies use modelling approaches to upscale
o Models are uncertain, particularly for large catchments
o Models are not always persuasive to public/policymakers
o We don’t have enough empirical data on all the processes (i.e. exactly how debris dams slow the flow) Upper Severn and Avon Catchment
* All models are wrong (but some are useful

32
Q

Will restoration reduce flood peaks

A

Increased water store within storms (water tables and soil water storage; increased surface storage) – Holding water back on the hillslope
and/or
Slowing delivery of water by reducing overland flow and channel water velocity (surface and channel roughness) – vegetation and barriers reduce flow velocity
Shuttleworth et al., 2019

33
Q

How do you know if any hydrograph change is not just because of synoptic variation (i.e. you had a particularly dry period after the intervention)?

A

Measure before and after and control

34
Q

What are low flows?

A
  • Flow of water in a stream during prolonged dry weather
  • Seasonal
  • Natural component of the flow regime in any river or stream
  • Use flow duration stats to define
    o e.g. 7Q10 - lowest 7-day average flow that occurs on average once every 10 years
  • Predictable
35
Q

What is a drought (river)?

A
  • More than low stream flows
  • Water availability for various designated uses
  • Defined as reduction in surface water storage, decrease of stream flow discharge and lowering of groundwater levels over large areas, over one or more consecutive years
  • Difficult to predict
36
Q

What are the water quality issues in catchment systems

A
  • Organic pollution
  • Sewage
  • Agricultural runoff – nutrient pollution (N and P)
  • Heavy metal concentration
  • Sediment + contaminated sediments
  • Emerging pollutants
    o Volatile organic compounds
    o Microplastics
37
Q

Why are there Increasing episodes of sewage release?

A
  • Increasing populations
  • Increased urbanisation and impermeable cover, therefore higher urban discharges
  • Climate change, increased storm intensity and increased urban runoff
    o Sewage systems made in the 19th century – can’t handle the amount of runoff and sewage
  • The ‘discharge consent’ system allows disposal of liquid waste by companies
  • Combined sewage and runoff systems
38
Q

What is the EU Water Framework Directive?

A
  • “Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for community action on the field of water policy”
  • Requires that all inland and coastal waters within defined river basin districts must reach at least “good status” (originally by 2015 or 2027)
  • Defines how this should be achieved through the establishment of environmental objectives and ecological targets for surface waters
  • Adopted into UK law in 2003
  • Thinking about water quality on a catchment scale  before this catchments weren’t thought of as units
39
Q

Key features of the WFD 1

A
  • Establishes river basin districts (RBD) as the basic management units
  • For each RBD a river basin management plan (RBMP) must be developed by the ‘competent authority’ (e.g. the Environment Agency in UK)
  • Each RBMP must include a programme of measures for achieving water quality protection and improvement
  • Defining water quality and measures to improve it
  • Prime aims are environmental, but RBMPs also need to consider economic and social needs
  • An integrated approach
  • Requires systematic assessment of water quality status of all water bodies
  • Requires extensive monitoring programmes
  • RBMPs aim to
    o Prevent further deterioration of water quality
    o Achieve good status for all water bodies
40
Q

But just what is ‘good status’?

A
  • Status level = combo of ‘chemical status’ and good ‘ecological status’
  • Importance of High (near natural) status as a reference
  • Good status only ‘slight change’ from natural conditions
    –> what is a ‘slight change’?
41
Q

How might we establish high status (natural conditions) reference conditions for our water bodies?

A

Lake Windermere has high concentrations of phosphorus, causing eutrophication (see Maberly, 2009)

Paleolimnology
o Can see what was living and died in the lakes
o Diatoms – single celled organisms that are sensitive to water quality
o Cumming (1999)

42
Q

Steps of the EU WFD

A
  1. Define ‘high/good status’
  2. Characterise (in detail) river basin districts, including environmental impacts of human activity
  3. Assess present water quality conditions
  4. Identify water quality management issues and pollution control measures
  5. Consult with interested parties over these measures, costs and benefits
  6. Implement agreed control measures
  7. Monitor improvements in water quality
  8. Review progress and
  9. Revise water management plans
43
Q

North West River Basin Management Plan 2022
Reasons for not achieving good status

A

by business sector
* Agriculture and rural land management
* Water industry
* Urban and transport

44
Q

Managing diffuse pollution from rural areas
from EU water

A

Environment Agency/Natural England
Agricultural and rural land management (farm businesses)
Water industry and rural land management

45
Q

Managing diffuse pollution from rural areas
from EU water –> Environment Agency/Natural England

A
  • check and ensure compliance against environmental permits against requirements of a wide range of environmental legislation.
  • use opportunity mapping to identify and promote locations where woodland creation can achieve multiple benefits for the environment
  • Provide advice and training to farmers in some priority catchments through an approach such as Catchment Sensitive Farming
46
Q

Managing diffuse pollution from rural areas
from EU water –> Agricultural and rural land management (farm businesses)

A
  • comply with permits relating to spreading of waste to land for agricultural benefit, pig and poultry units, etc.
  • comply with the action programme measures within the Nitrate Pollution Prevention Regulations 2015
  • voluntarily participate in Countryside Stewardship and Countryside Productivity schemes to prevent deterioration, improve water quality
47
Q

Managing diffuse pollution from rural areas
from EU water –> Water industry and rural land management

A

work together in drinking water safeguard zones to reduce the need for water treatment as a result of nutrients or pesticides to meet drinking water standards.

48
Q

Aims of Catchment sensitive farming Run by Natural England

A
  • Save farms money by introducing careful nutrient and pesticide planning, reduce soil loss and help farmers meet their statutory obligations such as NVZs,
  • Deliver environmental benefits such as reducing water pollution, cleaner drinking water, safer bathing water, healthier fisheries, thriving wildlife and lower flood risk for the whole community Workshops, tailored advice, capital grants
49
Q

How can we Reduce the need for water treatment?

A
  • Buffer strips/riparian corridors
  • Headwater restoration
50
Q

Managing pollution from wastewater
NW river basin management plan 2015
Role of Environment agency:

A
  • grant and review environmental permits to the water industry, manufacturing and other sectors to protect the environment from pollutants in discharged effluent.
  • work with the water industry to develop a long-term strategy for sewerage to prevent deterioration of permitted discharges and minimise risks to the water environment from misconnected sewerage.
  • carry out a review of areas sensitive to eutrophication, in relation to the Urban Waste Water Treatment Directive (UWWTD) and make recommendations to Defra.
  • enforce restrictions and bans on the use of certain chemicals (with H&S inspectorate)
51
Q

Managing pollution from wastewater
NW river basin management plan 2015
Role of local government:

A
  • consider the impact on water quality in planning/development/management of new buildings and infrastructure.
52
Q

Managing pollution from wastewater
NW river basin management plan 2015
Role of all sectors:

A
  • consider the Marine Policy Statement and marine plans in decisions that affect marine and coastal environments
53
Q

Managing pollution from wastewater
Work with the water industry – engineered solutions

A
  • Retention storage
  • Can be released more slowly when the system is able to cope
  • High-rate clarification treatment
    o Sewer separation - would require changing the systems below ground
54
Q

Managing pollution from wastewater
Work with the water industry – enforce policy

A
  • Implementation of regulation such as discharge consents on point sources, permits and environmental damage legislation
  • Provision of pollution prevention advice and campaigning
  • Improvement of continuous and intermittent sewage effluent discharges
  • Policy is only as good as the current structures that are in place - Tory government slashed Environment agency funding
55
Q

Managing pollution from urban areas
Sustainable Drainage Systems (SuDS)

A

Limited infiltration in urban environments → drainage networks overwhelmed
SuDS use a sequence of techniques that together form a management train. To control flow velocity and pollutants

May include:
* source control methods (decrease the volume of water)
* pre-treatment steps, such as vegetated swales or filter trenches (remove pollutants)
* retention systems (delay discharge to watercourses)
* infiltration systems such as infiltration trenches and soakaways
* water enters the system slower – doesn’t overwhelm sewage systems

56
Q

WFD +ves

A

Many extremely positive aspects!
* Integrative and catchment-based approach
* Relies very heavily on key concepts and information from catchment science
* Uses extensive, systematically monitored water quality data
* A focus for tackling diffuse pollution
* Optimises water quality management strategies for individual catchments through River Basin Management Plans  recognises that individual areas have their own management needs

57
Q

WFD -ves

A
  • agreeing protocols and systems for classification
    o What is ‘slight’ deviation from high status?
    o What exactly should/can be measured?
  • there can be exclusions (water bodies where you don’t need to reach good status)
  • Constraints on realising the RBMPs and slow progress to good status
  • economic barriers (resourcing the plans)
  • political and institutional barriers
  • moving targets (e.g. climate change, Brexit) – things happen that are unexpected

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