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Water Resources RM > Water Supply Management > Flashcards

Water Supply Management Flashcards

1
Q

What is the UN definition of ‘water security’?

A

the capacity of a population to safeguard sustainable access to adequate quantities of acceptable quality water for sustaining livelihoods, human well-being, and socio-economic development, for ensuring protection against water-bourne pollution and water-related disasters, and for preserving ecosystems in a climate of peace and political stability.

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2
Q

What is virtual water?

A

Virtual water is water embedded in commodities

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3
Q

What is the waterfootprint?

A

The water footprint is the total volume of freshwater that is used to produce the foods and services consumed by an individual, business or nation

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4
Q

What three things can water infrastructure help with?

A

1) Protection against floods
2) Improving water quality
3) Ensuring water supply

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5
Q

Three points about the limits to infrastructure expansion

A
  • Infrastructure expansion for water supply is constrained (‘peak water limit’)
  • Marginal benefit of new infrastructures decreases with cumulative investment
  • It has substantial (often unanticipated) socio-economic-environmental costs
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6
Q

There’s a shift from ‘hard-path’ to ‘soft-path’ solutions through a….

A

growing emphasis on improving the productivity of existing infrastructure by making water management more efficient

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7
Q

5 main purposes of reservoirs?

A
  • Irrigation
  • Hydropower
  • Water supply (domestic and industry)
  • Flood control
  • Multiple purposes
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8
Q

Negative impacts of reservoirs?

A
  • Resettlement of inhabitants
  • River fragmentation, dams may affect the passage of migratory fish, can be partially overcome by constructing bypasses of fish ladders
  • Alteration of downstream flow regime
  • Sediment trapping, the dam blocks downstream transport of sediment, sediment accumulates in the reservoir (reservoir capacity diminishes in time), sediment supply to downstream areas is reduced (erosion of downstream river beds and banks)
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9
Q

Long term negative effects

A
  • Supply demand cycle

- Reservoir effects

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10
Q

What are water resources management plans?

A

They show how a water company propose to manage the supply-demand balance over a planning period of 25-years
They are produced every 5 years by the water company and need to be approved by the EA

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11
Q

3 aspects covered in water resources management plans?

A

1) The demand expected in a water resource zone (WRZ) across the 25-years planning period
2) The supply from each WRZ, incorporating the effects of changes in licences and climate change
3) The measures that will be implemented where forecast demand will exceed supply (e.g. leakage reduction, metering, water transfers, new reservoirs)

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12
Q

What are water resource system models?

A
  • Water resource system models are used to support the quantitative assessment underpinning the WRMP (supply side)
  • WRS models can simulate the movement of water through a water supply and distribution system, including reservoirs, pipes, treatment plans etc.
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13
Q

4 components of a reservoir

A

1) Dam
2) outlet from ‘outlet tower’
3) bottom outlet
4) spillways

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14
Q

7 different water fluxes

A

1) precipitation
2) seepage losses
3) inflow
4) evaporation
5) release (from outlets)
6) outflow (flow spillways)
7) outflow (from bottom spillways)

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15
Q

Where do inflows come from in a) reservoirs dammed in valley sides b) bank-side reservoirs

A

a) inflows come from upstream rivers and drainage catchment

b) inflows come from river abstraction

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16
Q

What is the evaporation equation?

A

E = e*S
where e = evaporation for squared meters (depends on local climate)
S = reservoir surface area

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17
Q

What is the surface area of the reservoir linked to?

A

SA is linked to the reservoir storage level and both are linked to the storage

The relationships between these variables depend on the geometry of the reservoir

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18
Q

Two methods of obtaining the stage-storage-area relationships

A

1) end area method

2) surface area method

19
Q

Explain the end area method in 3 steps

A

1) Valley cross sections are surveyed at various points
2) The end area of each cross section can be computed at selected values of water elevation (h)
3) The end area is multiplied by the horizontal distance between cross sections to obtain the storage (s) at each selected elevation

20
Q

Explain the surface area method in 3 steps

A

1) From a topographic map of the reservoir, estimate the reservoir surface area (S) at selected values of water elevation (h)
2) for each pair (h,S) compute the storage (s)
3) Interpolate the data pairs (h,s) and (h,S) to obtain the stage-storage curve and the stage-area curve

21
Q

When do spills take place?

A

Spills take place when the water level exceeds a threshold on the level, or equivalently a storage threshold (i.e. the reservoir (active) capacity)

22
Q

What is release?

A

This is a ‘controlled output’, in fact it depends on the operator’s decision (how much water one wants to take out of the reservoir). The simplest decision model is the Standard Operating Policy

23
Q

What is the Deployable Output (DO)?

A

The Deployable Output (or firm yield) is the maximum rate at which a system can supply water continuously through a dry period with a known or assumed severity

24
Q

Advantages of using historical drought to define the DO

A

1) Easier to communicate to the public, water companies aim to supply water through the worst drought in ‘living memory’
2) Allows for using simplified approaches to hydrological modelling for assessing the DO (or computing other performance indicators) whenever long flow records are available

25
Q

Disadvantages of using historical drought to define the DO

A

1) For ungauged catchments: estimating the worst drought using data from other catchments is possible but may provide inaccurate results
2) The worst drought in the available records might not be representative of future conditions, because of:
high variability of droughts along temporal scales (natural variability), hydrological changes due to climate change and land use change (human-induced variability)

26
Q

How can we estimate the DO?

A

The DO can be estimated by iteratively applying the reservoir simulation procedure.

27
Q

How is estimating the DO useful for reservoir sizing?

A

If the DO is smaller than the actual water demand then the reservoir is undersized

28
Q

Engineering objectives (e.g. water supply, flood control etc.) of WRS are often measured by indicators classified in 3 groups which are?

A

Reliability indicators - how frequently a WRS fails
Resiliency indicators - how quickly the WRS recovers from a failure
Vulnerability indicators - how severe the effects of a failure are

29
Q

Other options for defining vulnerability - squared deficits

And where does the uncertainty origionate from

A

Squaring is used to capture the non-linearity of the relationship between deficit amount and its consequences

The uncertainty origionates from the fact that we define the indicators from observable variables as a way to represent a process that are more difficult or even impossible to measure (proxy indicators)

30
Q

Other indicators of reservoir performance?

A

Reservoir purposes:

  • Water supply
  • Irrigation
  • Hydropower
  • Flood control

Adverse impacts

  • Resettlement of inhabitants
  • Sediment trapping
  • Loss of habitats and ecosystems
  • Dam safety and flood risk
31
Q

Possible indicators to measure benefits and costs of reservoir purposes and adverse impacts

A
  • Reliability, vulnerability, resilience of water supply
  • Crop yield
  • Surface area lost
  • Crop yield
  • Reduction in sediment transport
  • Loss of storage capacity
32
Q

Why are river flow regime relationships complex to model?

A

Processes interact at different spatial and temporal scales

Lack of data to build and validate models

33
Q

What we can do to help the modelling of river flow regime relationships as a part of ecosystem conditions?

A

Define a minimum flow requirement to support ecosystem functions (ecological flow or flow demand for ecosystems

Use the distance from such flow requirement as a proxy of the impacts on ecosystems conditions

34
Q

What are ‘ecological flows’ and ‘ecological functions’?

A

The ‘flow demand’ for ecosystems (or ‘ecological flow’) is the amount of flow that is needed to support ecosystem functions

  • Moderately high flows transport fine sediment and organic resources
  • Larger floods transport large wood, gravels and boulders
  • Low flow periods allow riparian plant species to establish themselves on river banks and floodplains
  • Floods that overtop riverbanks connect the channel to floodplains
35
Q

How to define the ‘flow demand’ through hydrological signatures

A

One way to define the flow demand is to define several signatures to characterize the natural flow regime. Each signature can be quantified via a set of indicators

36
Q

How do you measure the hydrological alteration?

A

The average distance between the hydrological indicators in natural conditions (pre-dam) and after dam construction is a measure of the hydrological alteration (and a proxy of the ‘damage’ to ecosystems)

37
Q

Analyses used to aid decision making

A
  • Cost-benefit analysis
  • Cost effectiveness analysis
  • Multi-criteria analysis
38
Q

Explain cost-benefit analysis

A
  • transform all performance indicators into monetary units
  • sum ‘costs’ and ‘benefits’ of each option
  • choose an option that maximises the net benefit
39
Q

Limitations of cost-benefit analysis

A

1) Difficult to monetise some objectives (e.g. environmental)
2) difficult to account for temporal distribution of costs and benefits (problem of defining the discount rate)3) Difficulty to account for different attitudes towards risk and uncertainty
4) Hide the distribution of costs and benefits across sectors

40
Q

Explain cost-effectiveness analysis

A
  • Set a target for each engineering and environmental indicator
  • Discard the options that do not achieve the targets
  • Among the remaining options, choose the one with lowest cost
41
Q

Limitations of cost-effectiveness analysis

A

it can hide trade-off between objectives

42
Q

What is multi-criteria analysis?

A

Relies on the concept of Pareto-dominance
Discard the options that are Pareto-dominated (at least one objective can be improved without worsening any other)

Limitations - choice within the set of pareto-efficient options is no univocal

43
Q

What are the 4 main global water related risks?

A

Flooding
Water scarcity
Inadequate water supply for sanitation
Ecosystem degradation and pollution

Water Resources RM (10 decks)

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