Flows- Swanage Bay

What are flows?

the movement of people, products, money and other things across time/space

Why study geographical flows?

• create links

• help understand patterns

• help plan distribution of resources

• help predict the future

• help understand how systems work

Name and describe the site of the investigation of flows.

Swanage Bay-

• a bay on the

• East Coast of the

• Isle of Purbeck

• in southern England- Dorset

What is the enquiry question?

How do coastal management strategies affect the natural sediment flow in Swanage Bay?

What are the key questions?

Why does Swanage Bay need coastal management?- link to sediment flow

What coastal management strategies are being employed?

How effective are the coastal management strategies?- link to impact on sediment flow

Describe the distribution of rock-types in Swanage Bay.

Bay is made of soft clay and sands

making it vulnerable to erosion

What are the coastal management objectives in Swanage Bay? (secondary information)

• protect economic viability

• protect core values + character of the center of Swanage

• reduce flood risk

• maintain beach widths + use

• manage risk to properties

• maintain geological exposures- World Heritage Site + SSSI

• maintain landscape, views + appreciation of coastal environment

• support adaptability of communities

• reduce reliance on defences

Why has there been no active intervention on the eroding cliff face?

no economic value

How is the center of the bay protected?

Hold the Line- groynes + recharge

How is the southernmost curve of the Bay protected?

Hold the Line- Sea Wall

What are the 4 methods of data collection undertaken?

Groyne drop height- to establish effectiveness

Field sketch

Beach Profile- assess difference between replenishment + non-replenished

Wave measurements

Groyne Drop Height: Describe

• type of data

• sampling strategy

• method

Primary, Pragmatic, Quantitative

1. Metre rule to measure drop from the bottom to the top of the groyne uprights.

2. Repeat for first 10 uprights on each groyne- both N/S sides.

3. Calculate average drop for N/S sides.

4. Share data with other groups- increase sample size + reliability

Groyne Drop Heights: Justify

• data collected

• data type

• sampling strategy

• reliability

measure of groyne effectiveness

• if sediment built up on one side, drop would differ, showing the groynes work in preventing sediment flow due to LSD

quantitative- easy to graph, compare, spot patterns

pragmatic

• time + numbers = first 10 groynes

• tourist heavy area → most important area- maintained the most

reliable as we took 10 measurements + avg.

Groyne Drop Heights: Evaluate

• pros and cons of method

Pros:

• we used metre rules with cm marking- accurate

• collated data with other groups- reliable

• relatively cheap- not much equipment

• easy- minimal skills required

Cons:

• beach wasn’t only affected by coastal erosion (reprofiling, road drainage)

• Groyne 5 had a surface draining pipe from the road- abnormally small south side

• data doesn’t represent prevailing conditions- short time

• access was tide-dependent

• we may have missed a trend on the other side of the beach

Field Sketch- describe

• type of data

• method

Qualitative, Primary

1. We drew a basic sketch of Swanage Bay.

2. Annotations- defences, groynes, beach huts

   • anything that could alter the cost benefit of sea defenses

Field Sketch: Justify

• data collected

• data type

clear- lack of unnecessary details

• better than photograph

very fast

minimal equipment needed

Field Sketch: Evaluate

• pros and cons of method

Pros:

• Very fast, clear

• minimal equipment needed

• simple

• important aspects highlighted

Cons:

• scale could be inaccurate- impacting analysis

• features may be invisible to the naked eye

Wave measurement: describe

• type of data

• method

• working out

Quantitative, Primary data

1. Choose point at end of groyne.

2. Time a minute, count waves past point, record.

(>13 waves = destructive waves)

1. Throw an apple into the sea and mark place with ranger pole.

2. Wait a minute, find where it ended up.

3. Set another pole at end location and measure distance between poles.

Wave measurement: justify

• data collected

• method

accuracy:

• tape measure used- precise to the mm

• carried out in 2 areas to compare results

data:

• easy to find constructive/destructive

Wave measurement: evaluate

• pros and cons of method

pros:

• easy to do

• minimal equipment

• quick

cons:

• data only represents a part of the beach

• on the day, the winds blew NE, so LSD carried sediment in the opposite direction than it normally does

Beach profiles: describe

• data types

• method

Primary

Systematic

• areas chosen to cover space between each groyne

1. Set up ranger pole at edge of wet sand

2. Set up next pole 2m into the beach with tape measure.

3. Use a clinometer, place it at 1st pole and align with same point on next pole.

4. Identify angle and record.

5. Place 1st pole 2m inland from the 2nd, repeating process until sea wall.

6. Repeat at another point- one nourished, one not.

Beach profile: justify

• data collected

• data types

Systematic:

regular intervals removes bias + allowed the coverage of large area

• measuring the change in angle from sea wall to sea meant we could measure the effect of nourishment on gradient of land.

Beach profile: evaluate

• Pros and cons

Pros

• simple + easy

• quick

Cons:

• incorrect readings of clinometer

• skewed data by human activity

• area covered depends on the tide

Groyne Drop Height: presentation

• name the presentation

• justify

• bar graph

• clear and easy to interpret trend

• visual and numerical representation

• reading off the actual value is hard

Wave fq and direction: presentation

• name the presentation

• justify

• rose diagrams

• easy visual representation

• not difficult to interpret

• size = frequency

LSD direction + distance: presentation

• name presentation

• justify

• Flow lines- arrows on maps

• visually clear

• simple conversion scale

• time consuming

Beach profile: presentation

• name presentation

• justify

• use beach profile calculator

• put in values + angles to generate a slope

• easily understandable

• data represented clearly

Field sketch: presentation

• name

• justify

• field sketch

• only important features drawn

Flows analysis

• field sketch

• groyne drop

• beach profile

sketch

• showed strategies were wall, groynes (and replenishment)

groyne drop height:

• drop on south-facing side less than north-facing side

• Groyne 5 was by a sewage outlet so extra sand was eroded

• overall trend- groynes are trapping sediment flowing from the south.

wave measurements:

• LSD went N→S- anomaly on day

beach profile:

• beach is wider where nourishment happened in 2005/6

• showed it has worked

Flows conclusion

• why management

• what’s used

• how effective

• coastal erosion → LSD → in northerly direction → decreased beach → tourism impact

• groynes along coast, sea wall, nourishment

• groyne on south side- 73.7

• groyne on north side- 83.3

• shows they have worked in stopping build up

Groyne drop: evaluation

• accuracy

  • enhanced + issues + improvements

• careful measurements with a rigid ruler- no slack + no sinking into sand

• tide affected access

• better by replicating in 2 locations

Groyne drop: evaluation

• reliability

  • enhanced + issues + improvements

• measured at multiple points + averaged

• pragmatic sampling- only closest areas to town

• better my multiple people measuring + discounting anomalies + averaging

LSD with apple: evaluation

• accuracy

  • enhanced + issues + improvements

• timing with stopwatch = exact time

• apple may not act like sediment

• better by using painted pebble instead of apple

LSD with apple: evaluation

• reliability

  • enhanced + issues + improvements

• measuring in s and mm- smallest units

• lack of repeats of experiment

• repeat in multiple tidal conditions

Beach profile: evaluation

• accuracy

  • enhanced + issues + improvements

• using a clinometer- accurate angles

• room for error in reading of measurements

• better by having multiple people read value

Beach profile: evaluation

• reliability

  • enhanced + issues + improvements

• systematic sampling- every 2m removed bias

• only 1 measurement taken + only in 2 areas- one nourished/one not

• better by measuring more points, more areas and take averages