Simulation of River Flow for Downstream Water Allocation in the Heihe River Watershed, Northwest China - Landscape Ecology for Sustainable Environment and Culture - page 175

Observed 1978-1987 1990-2000 Precip

3

2

1

1.0E-01 0

8.0E-02

6.0E-02

4.0E-02

2.0E-02

0.0E+00

1/1/90 2/20/90 4/11/90 5/31/90 7/20/90 9/8/90 10/28/90 12/17/90

Fig. 9.4 Comparison of the simulated discharges and observed discharge in the Heihe River for

1990

Wu et al. 2010 ). Fourth, lack of detailed soil attribute and aquifer information led
to the failure of the DLBRM to detect the movement of groundwater in the study.
The simulated average annual flow for 1990-2000 was about 1.05 9 10 9 m 3 at
the middle reach outlet (at Zhengyixia Gage Station) under a normal precipitation
year (P = 50 %). But the annual river flow was simulated to change from
0.80 9 10 9 m 3 in 1991 (a dry year, P = 75 %) to 1.27 9 10 9 m 3 in 1998 (a wet
year, P = 20 %). It appears that under normal climatic years, the amount of flow
passing the middle reach outlet is slightly over 1 9 10 9 m 3 , barely satisfying the
requirement of delivering 0.95 9 10 9 m 3 downstream annually by the State
Council. This amount of flow, however, only has an exceedence probability of
50 %, meaning that the annual river flow is less than 1 9 10 9 m 3 at Zhengyixia
Gage Station 50 % of the time. In addition, the simulations of 1990-2000 over-
estimated the actual flow by 40 % (Fig. 9.3 ). The simulated daily flows for 1999
underestimated the discharges during the cold season, and overestimated the dis-
charges during the spring and summer (Fig. 9.4 ) (He et al. 2009 ). These dis-
crepancies are related to both the model structure and data availability and
accuracy. First, the DLBRM was developed to simulate hydrological processes of
North America's Great Lakes watersheds, and does not have explicit modules
available to simulate either permafrost processes or river channel infiltrations to
aquifer, which leads to its underestimation of discharges during the winter season
and overestimation of the discharges in the warm season, respectively. Second,
lack of data on detailed soil attributes and aquifer settings made the DLBRM
unable to discern the groundwater flows to the river. Third, it seems that large
storages of water in the reservoirs for the increased irrigation withdrawals in the