Stream Channel Incision Following DrainageBasin Urbanization

1
Stream Channel Incision Following Drainage-Basin
Urbanization

• Booth, D.B
• Josh Hackett and Marina Drazba

2
Runoff
3
Runoff
4
Study Site
Geology low-permeability till, lacustrine
deposits, and bedrock below permeable soil
developed beneath the forest.
Precipitation low intensity, canopy interception
is significant in the hydrologic balance.
Interception Infiltration capacities of
undisturbed soils are rarely exceeded.
Runoff Largest runoff peaks are produced by
multi-day storms, which raise the hillslope
groundwater tables.
5
Effects
Increased runoff
6
Hydrograph
7
HSPF Model
8
HSPF Model
9
(No Transcript)
10
Stream Channel
11
Incision of stream channels
12
Channel Incision
Flow and Sediment Parameters

• Incision is dependent on transport relative to
  flux

Flow competence tb ?wgdS tb is shear
stress ?w is water density d is flow depth g
is gravity S is energy gradient (slope)
Critical Shear Stress tcr a dms tcr is critical
shear stress dms is the median sediment diameter
Slope and grain size control incision Topo
and geologic maps can be used to identify erosion
susceptible areas
13
Channel Incision
Identifying incision-susceptible localities

• Stream-power formulations (slope x discharge)
• Unit stream-power (stream-power per unit time per
  unit area)
• Shear stress

14
(No Transcript)
15
Channel Incision
Channel Characteristics
reducing slope limits incision
Low slope, High shear stress
16
LOD
17
Discharge Increase
18
Altered Stream Channel
19
Diverted Stream
20
Mitigation
21
Conclusions

• Urbanization increases runoff by decreasing
  storage
• Increase in runoff may lead to an incised stream
• Use maps and local geology to identify incision
  susceptible localities
• Mitigation can be as simple as a retention basin
  for storing the increased runoff to prevent
  incision