Integrated River Management - River Dynamics and Integrated River Management - page 771

Fig. 11.57 (a) Velocity profile uppstream from a step, where flow depth was 0.22 m; (b) Velocity profile at the steplip,
where the step was 0.8 m high and the flow depth was only 0.08 m; (c) Velocity profile in a pool which was 0.5 m
downstream of the step with a flow depth of 0.3 m.

the channel bed (Wohl and Thompson, 2000; Wilcox and Wohl, 2007). Several debris flow events occurred
after the artificial step-pool system was instand, but the debris flows have been reduced to hyperconcentrated
flows when they passed the experimental reach. The high resistance created by the artificial steps caused
great velocity reduction and sediment deposition. The pools were filled with the debris flow deposits.
Nevertheless, the pools were partly restored after floods with low sediment concentrations.
Artificial step-pool systems create stable and diverse aquatic habitats. The habitat diversity index H R D R
(Table 11.4) distinct increased because of three primary aspects: (1) Water surface area is increased relative
to the natural channel, enlarging the area of aquatic habitat (2) streambed substrate became diversified.
Besides boulders, cobbles, and gravels in the natural condition, other substrates, such as silt, mud, and
even organic debris and water moss also appeared on the bed, and (3) the range of flow velocity expanded.
Before the artificial step-pool system the flow velocity was relatively uniform, typically from 0.4 to 1.0 m/s.
After the installed artificial step-pool system, flow velocities differed much more in various zones.
Surface flow velocity is low (0-0.2 m/s) in the sluggish water zone upstream of the steps. Near the step
crest, velocity rises to 1.5 m/s, or even higher. Flow velocity in pools fluctuates intensively, as the water
body entrains air bubbles, thereby increasing the concentration of dissolved oxygen. The biodiversity
was greatly increased after the artificial step-pool system installed. The taxa richness, S , increased from
17 under natural conditions to 22-37 after the artificial step-pool system installed. The abundance
increased from 62 ind/m 2 to 5217 ind/m 2 only nine months later, and the biodiversity index, B , also rose.

T able 11.4 Biodiversity and habitat diversity before and after the artificial step-pool system was installed

S Abundance
(ind/m P 2 P )

Dominant species
(Density of individual invertebrate)

Sampling date H D B

Natural
channel

Hydropsychidae (17), Baetidae (9), Haliplidae,
Haliplus sp (7)

Jun 13, 2006 12 17 61.5 9.5

Baetidae (492), Simuliidae (150), Tipulidae, Antocha
(65)

Jun 28, 2006 22 37 881.5 11.3

Baetidae, Baetis (330), Baetidae, Baetiella sp. (70),
Chironomidae sp 1 (57), Chironomidae sp 2 (48)

Sep 11, 2006 12 28 612.8 10.8

With artificial
step-pool
system

Baetidae, Baetis (445), Baetidae, Baetiella sp
(257), Heptageniidae, Iron sp. (139),
Hydropsychidae, Ceratopsyche sp. (66)

Nov 12, 2006 30 35 1087.5 11.7

Baetidae, Baetis (3280), Chironomidae sp. 1 (1394),
Chironomidae sp 2 (186), Chironomidae sp 3 (124),
Baetidae, Baetiella sp (78), Grouvellinus sp (39)

Mar 11, 2007 42 22 5217 10.4