Table 4.4: Major principal sources and impacts of sedimentation

Pertinence Sector Action or mechanism Impacts
Source: Adapted from Environment Canada (2005a),  
Note: Water transforms landscapes and moves large amounts of soil and fine-grained materials in the form of sediment.
Sediment is: 1) eroded from the landscape, 2) transported by river systems and eventually 3) deposited in a riverbed, wetland, lake, reservoir or the ocean. Particles or fragments are eroded naturally by water, wind, glaciers, or plant and animal activities with geological (natural) erosion taking place slowly over centuries or millennia. Human activity may accelerate the erosion. Material dislodged is transported when exposed to fluvial erosion in streams and rivers. Deposition occurs as on flood plains, bars and islands in channels and deltas while considerable amounts end up in lakes, reservoirs and deep river beds.
 Agriculture areas, downstream catchments Agriculture
  • poor farming with excessive soil loss
  • increase soil erosion
  • add toxic chemicals to the environment
  • sediment and pollutants are added to streams
  • irrigation systems maintenance cost increased
Forest and development access areas, downstream catchments Forestry, Road Building, Construction, Mining
  • extensive tree cutting
  • lack of terrain reforestation
  • lack of runoff control in steep terrain
  • increase natural water runoff
  • accelerated soil erosion creating more sediment
Major rivers and navigable waterways Navigation
  • deposition in rivers or lakes
  • dredging (streams, reservoirs, lakes or harbors)
  • decreases water depth making navigation difficult or impossible.
  • releases toxic chemicals into the aquatic or land environment.
 Aquatic ecosystems Fisheries / Aquatic habitat
  • decreased light penetration
  • higher suspended solids concentrations
  • absorbed solar energy increases  water temperature
  • carrying toxic agricultural and industrial compounds
  • settling and settled sediment
  • affects fish feeding and schooling practices; can reduce fish survival
  • irritate gills of fish, can cause death, destroy protective mucous covering n fish eyes and scales
  • dislodge plants, invertebrates, and insects in stream beds affecting fish food sources resulting in smaller and fewer fish, increased infection and disease susceptibility
  • stress to some fish species
  • release to habitat causes fish abnormalities or death
  • buries and suffocates eggs
  • reduces reproduction
Lakes, rivers, reservoirs as water supplies Water supply
  • increased pump/turbine wear
  • reduced water supply usability for certain purposes
  • additional treatment for usability required
  • affects water delivery, increases maintenance costs
  • reduces water resource value and volume
  • increased costs
Hydroelectric facilities Hydropower
  • dams trap sediment carried downstream
  • increased pump/turbine wear
  • diminished reservoir capacity
  • shortened power generation lifecycle
  • higher maintenance, capital costs.
All waterways and their ecosystems Toxic chemicals
  • become attached or adsorbed to sediment particles
  • transported to and deposited in, other areas
  • later release into the environment.

Source: UNESCO  The United Nations World Water Development Report 2
Section 2: Changing Natural Systems,
Chapter 4, Part 2. Nature, Variability and Availability, p.134

Related publication:
Water Resources homeWater Resources
Other Figures & Tables on this publication:

Table 4.1: Precipitation distribution into surface water and groundwater components (by climate region)

Table 4.2: Selected large aquifer systems with non-renewables groundwater resources

Table 4.3: Water availability information by country (AQUASTAT, FAO 2005)

Table 4.4: Major principal sources and impacts of sedimentation

Table 4.5: Freshwater pollution sources, effects and constituents of concern

Table 4.6: Spatial and time scales within which pollution occurs and can be remediated

Table 4.7: Potential applications for reclaimed water

Figure 4.1: Global distribution of the world’s water

Figure 4.2: Schematic of the hydrologic cycle components in present-day setting

Figure 4.3: Oxygen-18 content of stream water along the main stem of large rivers

Figure 4.4: Variations in continental river runoff through most of the twentieth century (deviations from average values)

Figure 4.5: Typical hydrographs in accordance with climatic settings

Figure 4.6: Acid rain and its deposition processes

Figure 4.7: Five-year mean of the pH level in rainfall in the eastern regions of Canada and the US

Figure 4.8: Primary sources of groundwater pollution

Map 4.1

Map 4.2

Map 4.3: Groundwater abstraction rate as a percentage of mean recharge

Aral Sea