STREAMS
Hydrologic Cycle and Water Distribution on Earth
Ocean is by far the biggest reservoir. Of fresh water reservoirs, glaciers are by far
the largest reservoir.
Streams-channel
Drainage Basin, Watershed
Drainage Divide
Sediment Load
Velocity and DISCHARGE
Bedload/Suspended load/dissolved load
Gradient and Baselevel
If the river is above baselevel, it tends to cut down and erode the landscape, if it is
below baselevel it tends to deposit and fill in the surrounding landscape
Alluvial Fans and Deltas-drop in velocity/deposition of sediment
Channel and Floodplain evolution
Cutbanks, Meanders, Point Bars
Oxbow lakes
Floodplain
Levees
Discharge = volume of water per unit time traveling down the river
Can be calculated by measuring velocity and area of channel
Channels tend to meander across the floodplain with time
FLOODING
Water overflows channel banks
Natural rivers often flood every 2 or 3 years (small)
Larger floods occur less frequently
Some human changes to streams: covering of land-impermeable surfaces, channelization
of stream
Flood Frequency Curves: express probability of flood size as a “recurrence interval”
PROBABILITY is the key concept here.
Short record of stream vs. long record changes calculation
Development and Modification in the Floodplain
Increase in impermeable Surfaces (roads, parking lots, etc)
Surface runoff
Peak lag time shortened
Channelization
Straightening and stablization of the bank
May help upstream flooding-increases flow and gradient
May increase downstream flooding-increases amount of flow
Dams
Benefits include hydroelectric power generation, flood control, stable amount of
water flow throughout the year for irrigation
Drawbacks include flooding of the area behind the dam, changes in the sediment
budget for the river system (loss of nutrients onto the floodplain and delta), leaching of
the soil (Nile river case)
Levees-sedimentation in channel, raises level of channel (NO Miss. River was 10-15 feet
higher than Jackson Square