This document discusses surface water and streamflow generation. It summarizes that a watershed is the area of land that drains into a stream, and streamflow is the movement of water through channels via surface and subsurface flow, influenced by climate, land cover, and soil. Streamflow is generated through three main mechanisms: 1) Hortonian overland flow during heavy rain on impervious surfaces, 2) subsurface flow through lateral movement of water in the soil, and 3) saturation overland flow when the soil is saturated from below and precipitation becomes overland runoff.

1. Surface water
 Watershed – area of
land draining into a
stream at a given
location
 Streamflow – gravity
movement of water in
channels
 Surface and subsurface
flow
 Affected by climate,
land cover, soil type, etc.

2. Sources of streamflow
http://uregina.ca/~sauchyn/geog327/outline.html

3. Streamflow generation
 Streamflow is generated by three mechanisms
1. Hortonian overland flow
2. Subsurface flow
3. Saturation overland flow
 Some texts mention groundwater ridging as an
additional mechanism contributing to streamflow

4. Welcome to the Critical Zone

5. Denudation
Weathering front
advance
Erosion and
weathering
control the extent
of critical zone
development

6. Sediment
Water,
solutes and
nutrients
Critical zone
architecture
influences sediment
sources, hydrology,
water chemistry and
ecology

7. Boulder
Golden
The Colorado Front Range
Fort
Collins

8. Boulder
Golden
Fort
Collins
The Boulder Creek watershed
Limits of glacial
and fluvial rejuvenation
•Precambrian crystalline bedrock
•Uniform climate history
•Three erosional states

9. Boulder Creek Critical Zone Observatory
Slope map draped over shaded relief.
Glacial limits
•How do weathering
and transport
processes control the
structure of the CZ?
•What is the impact of
CZ structure on
hydrological,
geochemical and
biological functions?

11. Three experiments in one:
the geomorphic context of Boulder Creek
Upper: glaciated
Middle: steady, old
Lower: rejuvenated

12. Front Range ‘Rocky mountain surface’

13. Lower: Boulder Canyon-Betasso

14. fracture
zone
5m
5m
bedding
weathered
rock
soil
water flow path
Oregon Coast Range- Coos Bay
Anderson et al., 1997, WRR.
Montgomery et al., 1997, WRR
Torres et al., 1998, WRR
Channel head

15. Hortonian Flow
 Sheet flow described by
Horton in 1930s
 When i<f, all i is absorbed
 When i > f, (i-f) results in
rainfall excess
 Applicable in
 impervious surfaces (urban
areas)
 Steep slopes with thin soil
 hydrophobic or compacted
soil with low infiltration
Rainfall, i
Infiltration, f
i > q
Later studies showed that Hortonian flow rarely occurs on vegetated surfaces in humid regions.

16. Subsurface flow
 Lateral movement of water occurring
through the soil above the water table
 primary mechanism for stream flow
generation when f>i
 Matrix/translatory flow
 Lateral flow of old water displaced by
precipitation inputs
 Near surface lateral conductivity is greater than
overall vertical conductivity
 Porosity and permeability higher near the ground
 Macropore flow
 Movement of water through large conduits in the
soil

17. Soil macropores

18. Saturation overland flow
 Soil is saturated from below by subsurface flow
 Any precipitation occurring over a saturated surface becomes
overland flow
 Occurs mainly at the bottom of hill slopes and near stream banks

19. Streamflow hydrograph
 Graph of stream
discharge as a
function of time at a
given location on the
stream
Perennial river
Ephemeral river Snow-fed River
Direct runoff
Baseflow