An overfill ratio in beach nourishment design is used to
Answer: A
A ratio above one indicates more fill is needed than the simple volume calculation suggests. It is estimated from the grain size statistics of the borrow and native materials. Ratios well above one indicate a poor borrow source.
Please log in or register to report this question.
Cross shore transport differs from longshore transport in that cross shore transport
Answer: B
Correct answer: redistributes sediment within the profile rather than along it
Cross-shore transport moves sediment up and down the profile - offshore into bars during storms, back onshore during calm periods - so the material generally stays within the same stretch of coast. Longshore transport moves it along the coast and can remove it from the frontage altogether. Distinguishing the two matters, since a beach flattened by cross-shore transport will recover and one drained by longshore drift will not.
Please log in or register to report this question.
Consider the following statements comparing the two transport modes.
1. Cross shore transport is largely reversible over a season.
2. Longshore transport produces a net movement along the coast.
3. Cross shore transport is the main cause of long term shoreline retreat.
Answer: C
The first two are correct and give the essential distinction. The third is generally wrong, since long term retreat usually reflects a longshore or budget deficit instead. Seasonal exchange and long term trend are distinct.
Please log in or register to report this question.
A shoreline that is retreating steadily over decades most likely has
Answer: D
Persistent retreat implies losses exceeding supply over the long term. Identifying which budget term is responsible is the first step towards any sensible response. Treating a symptom without the cause rarely succeeds.
Please log in or register to report this question.
Assertion (A): Distinguishing storm response from long term trend is essential in coastal monitoring.
Reason (R): A beach may recover fully from a storm while still retreating over decades.
Answer: A
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the difficulty. A single storm can cut a beach back dramatically and the beach can rebuild fully over the following months, so a survey taken just afterwards shows an alarming loss that means nothing. Conversely a slow retreat of half a metre a year is invisible in any one year and is what actually threatens the frontage. Only a record of a decade or more separates the two.
Please log in or register to report this question.
State whether the following is true or false.
A single storm's erosion is not evidence of a long term erosion trend.
Answer: B
Correct answer: True
Storm erosion is largely cross-shore: sand is drawn offshore into bars and returns over the following calmer months. A trend requires a net loss from the system, which is a matter of the sediment budget rather than of any one event. Acting on a post-storm survey as though it showed a trend has led to a great deal of unnecessary defence, which is why the distinction is drawn so firmly.
Please log in or register to report this question.
Match each monitoring technique with what it provides.
List I
A. Beach profile survey
B. Aerial photography
C. Airborne lidar
D. Wave buoy
List II
1. high resolution topography over long frontages
2. cross sectional change at fixed lines
3. the incident wave climate driving the change
4. planform shoreline position over time
Answer: C
Correct answer: A-2, B-4, C-1, D-3
Each technique answers a different question. A profile survey measures cross-sectional change along fixed lines, which is what volume calculations require. Aerial photography gives the planform position of the shoreline through time. Lidar covers long frontages in three dimensions at high resolution. And a wave buoy records the forcing, without which the observed changes cannot be attributed to a cause.
Please log in or register to report this question.
Shoreline position is most commonly defined for mapping purposes as
Answer: D
Consistency of the definition matters more than which definition is chosen. Comparing positions defined differently is a common source of spurious change in historical analyses. Definition matters more than which one is chosen.
Please log in or register to report this question.
Assertion (A): Historical shoreline change analyses must use a consistent shoreline definition.
Reason (R): Different definitions can differ by more than the change being measured.
Answer: A
Both are true and the reason gives the risk, and tidal state at the time of a photograph matters greatly. Correcting for it is a standard step in shoreline change analysis. Tide state can shift the wet-dry line many metres.
Please log in or register to report this question.
Long term shoreline change rates on eroding sandy coasts are commonly of the order of
Answer: B
Correct answer: a fraction of a metre to a few metres per year
Typical long-term retreat rates on eroding sandy coasts run from a few tenths of a metre to a few metres a year, with soft cliffs at the upper end. Small as they sound, they accumulate to tens or hundreds of metres over the life of a building, which is why setback lines are drawn on a hundred-year projection and why the rate must be measured over a long record.
Please log in or register to report this question.
