Managing river and coastal environments: A continuing challenge 2010 China floods Duration10 May - Present Damage41 billion US$ Fatalities dead, 11,800+ missing or buried Area affected 28 provinces, autonomous regions and municipalities Source: Wikipedia

Managing river and coastal environments: A continuing challenge Why? Heavy downpour in summer Summer monsoon Onshore winds Low pressure centre over Asia Mudflow / landslide Overflow of rivers

Managing river and coastal environments: A continuing challenge 2Managing river and coastal environments: A continuing challenge

Managing river and coastal environments: A continuing challenge 2.1How does water shape our rivers and coasts?

Managing river and coastal environments: A continuing challenge A large crack along the coast at Cheung Chau (Credit: Liang Wing Hang Yanchap) crack A narrow ridge of sand in Greece (Credit: Corbis) A lake in New Zealand (Credit: NSIL) Cheung Chau Islands (Credit: The Government of Hong Kong Special Administrative Region)

Managing river and coastal environments: A continuing challenge Do you know what agents shape these landscape? They are shaped by rivers and waves. Let’s study some basic knowledge about river and coast before we learn how rivers and waves shape the land.

Managing river and coastal environments: A continuing challenge How does water move on our earth? Main storages of water AtmosphereLandOcean Soil and rocks Rivers and lakes Vegetation cover Water moves among the storage areas on the earth. The main storages are: Ice caps

Managing river and coastal environments: A continuing challenge How does water move on our earth? condensation surface run-off infiltration subsurface run-off transpiration evapotranspiration evaporation atmosphere rivers and lakes ocean soil and rocks vegetation cover precipitation

Managing river and coastal environments: A continuing challenge How does water move on our earth? interception precipitation transpiration evaporation stem flow drip flow Vegetation cover

Managing river and coastal environments: A continuing challenge Surface run-off evaporation precipitation overland flow channel flow surface run-off How does water move on our earth?

Managing river and coastal environments: A continuing challenge Water movement underground unsaturated rock and soil water table saturated rock impermeable rock surface storage soil moisture storage infiltration absorption ground water storage percolation evaporation throughflow base flow subsurface run-off How does water move on our earth?

Managing river and coastal environments: A continuing challenge If trees are cut down, how will the water cycle change? If there is deforestation … Test yourself! Interception will ( increase / decrease ); surface run-off will ( increase / decrease ); infiltration will ( increase / decrease ). Some map skills about rivers

Managing river and coastal environments: A continuing challenge The running water of the Jinsha Jiang (Credit: Tsui Chung Pong David) How does a river shape the land? Rivers can split rocks and cut into land; carry stones and sand along; drop the carrying stones and sand in places where their energy drops. Rivers are a significant agent that shape the landscape. Erosion Transportation Deposition

Managing river and coastal environments: A continuing challenge How does seawater shape our coast? An isolated mass of rock near Jeju Island, Republic of Korea (Credit: Liang Wing Hang Yanchap) Tides and waves are also agents that shape the coast. Waves can be either erode the land or deposit sediment there. Tides have significant impact on the formation of coastal landform.

Managing river and coastal environments: A continuing challenge How does seawater shape our coast? Tidal range There are two high tides and low tides every day. High tide – Low tide = Tidal range Active zone of wave action The larger the tidal range, the larger the zone of active wave action.

Managing river and coastal environments: A continuing challenge How does seawater shape our coast? Lowest water level Highest water level where storm waves can reach Zone of wave attack

Managing river and coastal environments: A continuing challenge How does seawater shape our coast? Foreshore Lowest water level Shore High tide level

Managing river and coastal environments: A continuing challenge How does seawater shape our coast? Backshore Foreshore Lowest water level Shore High tide level Highest water level Offshore

Managing river and coastal environments: A continuing challenge

1 Defining the area of a drainage basin Can you identify the watershed of River basin A on the map? First, identify the ridge that separates the basin from adjacent ones. Second, use a curved line to join the ridge and the highest parts down the spurs. Cut every contour line at right angle on its way. Last, close the watershed at the mouth of the river. River basin A

Managing river and coastal environments: A continuing challenge 2 Drainage density of a river Scale: 1:100,000 Drainage basin Channels Drainage density of the river = ___________________________ Total length of the channels in a drainage basin Total area of the drainage basin Total length of the channels = 21 cm  100,000 = 2,100,000 cm = 21 km

Managing river and coastal environments: A continuing challenge Drainage density of a river Scale: 1:100,000 Drainage density of the river = ___________________________ Total length of the channels in a drainage basin Total area of the drainage basin 0.5cm Complete squares = 55 squares

Managing river and coastal environments: A continuing challenge Scale: 1:100, Drainage density of a river Incomplete squares =35  0.5 = 17.5 squares Complete squares +Incomplete squares = = 72.5

Managing river and coastal environments: A continuing challenge 2 Drainage density of a river On the map, 1 cm = 100,000 cm (1 km) in actual; 0.5 cm = 50,000 cm (0.5 km) in actual The actual area of each square = 0.5 km  0.5 km = 0.25 km 2 The total area of the drainage basin = 0.25 km 2  72.5 complete squares = km 2

Managing river and coastal environments: A continuing challenge 2 Drainage density of a river Drainage density of the river Total length of the channels in a drainage basin = Total area of the drainage basin 21 km = km 2 = 1.16 km/km 2 The higher the drainage density, the more ( active / inactive ) the erosional force in the basin. Discussion : How will deforestation affect drainage density?

Managing river and coastal environments: A continuing challenge 3 Identifying different features of a river River A River source Confluence point Main river Tributaries

Managing river and coastal environments: A continuing challenge 4 Finding out the stream order River A Stream order = stream hierachy 1 First order streams 2 Second order streams 3 Third order streams 4 Fourth order streams This is a fourth order basin. Discussion: What is the difference in stream order between a river basin in TRF and a river basin in desert?

Managing river and coastal environments: A continuing challenge Identifying the ridges on a contour map A ridge A ridge is an elongated area of relatively high ground.

Managing river and coastal environments: A continuing challenge Is this a spur? B A Height (m) A B The cross-section of AB Identifying the spurs on a contour map