Precipitation-work 沉淀物估算网络PPT课件.ppt

Precipitation – work
Precipitation varies both in time and space

Sound hydrologic/hydraulic designs require adequate
estimation of temporal/ spatial precipitation patterns.
 
The density of rain work depends on
(1) purpose of the study;
(2) geographic configuration of the study region;
(3) economic consideration.
Rain Gauge Density in HK
Rain gauge density in HK is:
· Daily km2/gauge
· Autographic/ Automatic km2/gauge
 
Rain gauge density is significant higher in Hong Kong Island and much sparse relatively in New Territory (see figure).
Type
Number of Stations
Location Map
HKO Automatic Weather Station Rain Gauges
18
Figure 2
GEO Rain Gauge Stations - Telemetered
86
Figure 2
DSD Rain Gauge Stations - Telemetered
9
Figure 2
HKO Conventional Rain Gauge Stations
51
Figure 3
HKO Automatic Reporting Rain Gauges
21
Figure 2
Conventional Raingauge Locations in HK
Telemetered work in HK
World anization (WMO) Suggestion
A minimum density for precipitation work: (at least 10% are automatic recording gauges)
I: Flat region of temperature, Mediterranean & tropical zones;
IIa: Mountain region of temperate, Mediterranean & tropical zones
IIb: Small mountains island with very irregular precipitation requiring
very dense work
III: Arid and polar zones
Errors Precipitation Measurement
1. Human Error: scale reading & water displacement (if a
dip stick is used)
2. Instrumental Defect: water to moisten the gauge; speed at
which mechanical devices work (such as tipping bucket
gages); & inadequate use of wind shield
3. Improper Siting: height above ground of the gage orifice;
exposure angle; & regionalization techniques
 
(Ref: “Uncertainties in Estimating the Water Balance of Lakes,” by T. C. Winter, Water Resources Bulletin, AWRA, 17(1), 1981)
Rainfall Mass Curve & Hyetograph
Autographic Chart