River Ecology and Restoration - River Dynamics and Integrated River Management - page 687

(Continued)

Sturgeon prefer spawning areas with flow velocity of 0.08-0.14 m/s at the bottom,
0.43-0.58 m/s in the middle, and 1.15-1.70 m/s at the surface (Li, 2001). The surface
flow velocity at spawning areas is 1.1-1.7 m/s (Li, 1999). The flow velocity of spawning
areas during spawning season ranges from 0.82-2.01 m/s; 57.69% of fish are distributed
between 1.2-1.5 m/s. When spawning occurs during periods when water levels are
falling, the daily fluctuation range of flow velocity is 0.82-1.86 m/s, with an average of
1.24 m/s. The daily maximum fluctuation range is 1.20-2.33 m/s, with an average of
1.56 m/s. When spawning activity occurs during periods when water levels are rising, the
daily fluctuation range of flow velocity is 1.17-2.01 m/s, with an average of 1.55 m/s
(Wei, 2005). According to 31 records from 1983-2000, the average flow velocity on
spawning day was between 0.81-1.98 m/s, and 81% took place in the range of 1.00-
1.66 m/s (Yang et al., 2007).

Flow velocity
(spawning)

V 8

The suspended sediment concentration in reaches downstream from the Gezhouba Dam
is between 0.073-1.290 kg/m 3 , with an average of 0.508 kg/m 3 . About 66.67% of fish are
distributed between 0.3-0.7 kg/m 3 . When spawning activity occurs during periods of
falling water level, the daily average suspended sediment concentration varies between
0.17-1.29 kg/m 3 , with an average of 0.52 kg/m 3 . When spawning activity occurs during
periods of rising water levels, the daily average suspended sediment concentration varies
between 0.41-1.02 kg/m 3 , with an average of 0.61 kg/m 3 (Wei, 2005). The suitable range
of suspended sediment concentration for Chinese sturgeon is 0.10-1.32 kg/m 3 . From
1983-2000, 15 of 31 spawning events were in the range of 0.2-0.3 kg/m 3 (Yang et al.,
2007).

Suspended
sediment
concentration
(spawning)

V 9

10.3.4.5 Vegetation-Hydroperiod Modeling
Vegetation-Hydroperiod Modeling is a very useful tool for habitat evaluation. Hydroperiod is defined as
the depth, duration, and frequency of inundation and is a powerful determinant of what plants are likely
to be found in various positions in the riparian zone, as shown in Fig. 10.47. In most cases, the dominant
factor that makes the riparian zone distinct from the surrounding uplands, and the most important gradient
in structuring variation within the riparian zone, is site moisture conditions, or hydroperiod. Formalizing
this relation as a vegetation-hydroperiod model can provide a powerful tool for analyzing existing
distributions of riparian vegetation, casting forward or backward in time to alternative distributions, and
designing new distributions. The suitability of site conditions for various species of plants can be described
with the same conceptual approach used to model habitat suitability for animals. The basic logic of a
vegetation-hydroperiod model is straightforward. It is possible to measure how wet a site is and, more
importantly, to predict how wet a site will be. From this, it is possible to estimate what vegetation is
likely to occur on the site.
The two basic elements of the vegetation-hydroperiod relation are the physical conditions of site
moisture at various locations and the suitability of those sites for various plant species. In the simplest
case of describing existing patterns, site moisture and vegetation can be directly measured at a number of
locations. However, to use the vegetation-hydroperiod model to predict or design new situations, it is
necessary to predict new site moisture conditions. The most useful vegetation-hydroperiod models have
the following three components (FISRWG, 1997):
(1) Characterization of the hydrology or pattern of stream flow—This can take the form of a specific
sequence of flows, a summary of how often different flows occur, such as a flow duration or flood
frequency curve, or a representative flow value, such as bankfull discharge or mean annual discharge.
(2) A relation between streamflow and moisture conditions at sites in the riparian zone—This relation
can be measured as the water surface elevation at a variety of discharges and summarized as a stage vs.
discharge curve. It can also be calculated by a number of hydraulic models that relate water surface
elevations to discharge, taking into account variables of channel geometry and roughness or resistance to