IB+Fresh+Water

1. The water system The hydrological cycle Examine the inputs, outputs, stores and transfers of the hydrological cycle. Components of the basin hydrological system Inputs - in the forms of precipitation (rain or snow) Flow - where some of the water passes through a series of flows (e.g. infiltration, percolation, throughflow) Storage - where some of the water is stored in the lakes, soil or even ice Outputs - where the water is lost from the system either by the river carrying it to the sea or through evapotranspiration (loss of water directly from the ground, water surfaces and vegetation)

1.The Input Precipitation Refer to the deposition of moisture on the earth's surface from the atmosphere includes dew, hail (balls or irregular lumps of ice), rain, sleet (ice pellets) and snow. Forms the major input into the system through amounts vary over time and space.

2.The Storages Water from precipitation that reaches the basin may be stored temporarily in various forms: Interception storage Surface storage channel storage Soil moisture storage Ground water storage

(a) Interception http://www.physicalgeography.net/fundamentals/8k.html Defined as the capture of precipitation by the plant canopy and its subsequent return to the atmosphere through evaporation or sublimation. Some of the water that is intercepted never makes it to the ground surface. Instead, it evaporates from the vegetation surface directly back to the atmosphere. The key hydrological question concerns the extent to which interception alters the catchment water balance. The amount of precipitation intercepted by plants varies with leaf type, canopy architecture, (branching structure and leaf density), wind speed, available radiation, temperature, humidity of the atmosphere, magnitude and duration of precipitation, antecedent conditions of the canopy (i.e. whether it is saturated or not)

Surface Storage Occur in natural areas of impeded drainage such as lakes, reservoirs, ponds, drainage ditches and canals and canals. Also most apparent in urban areas for here the flat, impervious surfaces of roof tops, pavements and playing fields provide excellent sites for puddles.

Channel Storage Despite being the medium through which water drains from the system, channels also act as stores. They received their input indirectly through flows from other stores, and directly from precipitation that drops into them (i.e. channel precipitation). In times of flood, when the channel may overflow and take in the entire breadth of the flood plane, channel storage will be a major constituent of the system

Soil Moisture Storage When rain / meltwater enters the soil, a portion of it is stored in the pore spaces, while the remainder drains downward under the force of gravity. Depend upon the amount of precipitation (P) minus the amount loss by evaporation (E), plant transpiration (T) and drainage (D).

Soil Moisture = P – (E+T+D) Retention and availability of soil moisture depends on pore spaces type of soil vegetation soil condition (antecedent)

Groundwater Storage Approximately 22 % of the fresh water found at the Earth's terrestrial surface is stored as groundwater. Groundwater is specifically defined as the part of the subsurface water that fully saturates the pore space in bedrock, regolith or soil. The groundwater occupies the saturated zone. The upper surface of the saturated zone is called the water table. Groundwater is stored beneath the water table in the joints, pores, cracks and fissures in the rock which means that the amount of storage will vary according to the rock type. As the amount of groundwater increases or decreases, the water table rises or falls accordingly. When the entire area below the ground is saturated, FLOODING occurs because all subsequent precipitation if forced to remain on the surface. Groundwater returns to the surface through aquifers which empty into lakes, rivers, and the oceans. The flow of groundwater is much slower than runoff with speeds usually measured in centimetres per day, metre per year or even centimetres per year.

3. The Flows (Transfers) Throughfall and Stemflow A portion of the intercepted water can travel from the leaves to the branches and then flow down to the ground via the plant’s stem. This phenomenon is called stemflow. Another portion of the precipitation may flow along the edge of the plant canopy to cause canopy flow. Rain that falls through the vegetation, without being intercepted, is called throughfall.

Infiltration Infiltration – the process by whch water enters a permeable surface before moving downwards through the soil by Percolation. Infiltration capacity – the maximum rate at which the soil, in a given condition, can absorb water. It is expressed in units of depth per unit of time (cm/sec). Infiltration rate - rate at which soil absorbs rainfall

Movement of water (amount and rate) into the soil - is controlled by gravity, capillary action, and soil porosity.

Controls of Infiltration (a) Rainfall characteristics - rate of infiltration depends on the intensity of rainfall & soil infiltration capacity Surface runoff occurs when rainfall intensity exceeds infiltration capacity.

(b) Surface Controls Vegetation cover - interception - humus level (organic matter more porous & can hold greater quantity of water)

Soil surface state - surface sealing - compaction - impermeable pans - cracks & fissures

(c) Sub-Surface Controls Soil structure – ‘crumb-like’ soil (e.g. sand) allows for good drainage whilst horizontal plates (clay) impedes downward movement of water Soil texture – coarse textured soils have larger pores and fissures than fine-grained soils and therefore allow for more water flow. Cracks and macro-pores

Percolation As water moves through soils and rock layers it may reach more compact layers and its rate of movement slows down. The slow movement through these compact layers is called percolation. The process of percolation produces groundwater storage.

Difference between infiltration and percolation Water infiltration is water movement into the soil when rain or irrigation water is on the soil surface. This is when the water enters the soil through the surface. Percolation is the flow of more water through wetted soil. It is this percolating water moving through the soil which carries away nutrients and other salts dissolved from the soil.

Discuss the causes and consequences of the changing balance between water stored in oceans and ice.

The water balance Explain the concept of maximum sustainable yield of freshwater in terms of a balance between inputs and outputs.

2. Drainage basins and flooding Drainage basins Examine the functioning of a drainage basin as an open system with inputs, outputs, transfers, stores and feedback loops.

Discharge Define stream discharge. Examine its relationship to stream flow and channel shape.

Hydrographs Describe the characteristics of a hydrograph. Examine the reasons for spatial and temporal (short-term and long-term) variations in hydrographs. Examine the role of hydrographs in forecasting the magnitude, spatial extent and timing of floods.

Floods Discuss the natural and human causes and consequences of a specific river flood.

3. Management issues and strategies Dams and reservoirs Examine the hydrological changes resulting from the construction of dams and reservoirs. Examine the costs and benefits of dams and reservoirs as part of multi‑purpose schemes.

Floodplain management Explain the stream channel processes (erosion, transport, deposition) and explain the resultant landforms found on floodplains. Examine the human modifications of a floodplain and their effect on the size and probability of floods. Evaluate the costs and benefits of alternative stream management strategies.

Groundwater management Explain the functioning and management of artesian basins and aquifers, distinguishing between natural and artificial recharge. Examine the environmental impacts of groundwater abstraction.

Freshwater wetland management Describe the role of wetlands as a water resource. Evaluate the effectiveness of the management strategies that have been adopted in a major wetland.

Irrigation and agriculture Examine the environmental impact of agriculture and irrigation on water quality: salinization, agro‑chemical run-off, the pollution of groundwater and the eutrophication of lakes, rivers and wetlands.

4. Competing demands for water Conflicts at the local or national scale Examine the competing demands for water in a specific river basin. Evaluate the strategies that have been adopted to meet these demands.

Conflicts at the international scale Discuss an example of an international conflict related to freshwater.