this is my presentation of hydraulic and water resources engineering. I have discussed in this ppt about network density for given rain gauge and calculations and index of witness.

1. GUIDED BY:-
PROF . Ravi patel
PREPARED BY:-
Divyen devani 140050106018
Devanshi desai 140050106017
BITS EDU CAMPUS

2.  Rainfall data is the most important and
fundamental data required for all hydrological
investigations.
 They are required for,
 Analysing storms
 Fixing design flood
 Forecasting flood in a river
 Reservoir regulation

3.  The rain gauges density or network density is
define as the ratio of total area of the catchment
to the total number of rain gauges in the
catchment.
 To obtain reliable results , the various rain
gauges should be evenly and uniformly
distributed within a given catchment.
 The total number of rain gauges installed
within a given catchment area should neither
be too many as to be costly nor should be to
less as to give unreliable results.

4.  The world meterological organisation (WMO)
has laid down the following norms for
minimum network density.
Ragio
n
Description Network density
Minimum tolerable
1 Flat region of temperate,
mediterranean and tropical
zones.
1 gauge for 600 to
900𝑘𝑚2
1 gauge for 900 to
3000𝑘𝑚2
2 Mountainous area of
temperate, mediterranean
and trpical zones.
1 gauge for 100 to
250𝑘𝑚2
1 gauge fo 250 to
1000𝑘𝑚2
3 Arid and polar zones 1 gauge for 1500
to 10000𝑘𝑚2
-

5.  IS recommendations on raingauge density
 Is : 4987-1968 recommendends the following
raingauge densities
i. In plains – 1 station for every 520sq.km.
ii. In regions with average elevation 1000m – 1
station per 260-390 sq.km.
iii. In hilly areas with heavy rainfall – 1 station for
every 130 sq.km.

6. Optimum number of raingauges:
– The optimum number of raingauge stations that
should exist in order that the mean rainfall can be
estimated with an assigned percentage of error is
given by
Where,
N = optimum number of raingauges
𝐶𝑣= coefficient of variation of rainfall
E = allowable percentage error in estimate
of mean rainfall
𝐶𝑣 can be computed as follows:

7. 1. Calculate mean average annual rainfall
𝑃 =
𝑃
𝑛
where,
𝑃= total rainfall
= 𝑃1 + 𝑃2+….. 𝑃𝑛
n = number of raingauge
existing
2. calculate 𝑃 − 𝑃 2

8. 3. Calculate sample standard derivation
𝜎 =
𝑃− 𝑃 2
𝑛−1
4.Calculate the coefficient of variation
𝐶𝑣=
100×𝜎
𝑃

9.  Index of Wetness
 • Index of Wetness =
𝑎𝑐𝑡𝑢𝑎𝑙 𝑟𝑎𝑖𝑛𝑓𝑎𝑙𝑙 𝑖𝑛 𝑔𝑖𝑣𝑒𝑛 𝑦𝑒𝑎𝑟 𝑎𝑡 𝑎 𝑝𝑙𝑎𝑐𝑒
𝑛𝑜𝑟𝑚𝑎𝑙 𝑎𝑛𝑛𝑢𝑎𝑙 𝑟𝑎𝑖𝑛𝑓𝑎𝑙𝑙 𝑎𝑙𝑙 𝑎𝑡 𝑡ℎ𝑎𝑡 𝑝𝑙𝑎𝑐𝑒
 It gives an idea of the wetness of that year and hence
is a measure of the deficiency of rainfall. A 60% index
of wetness means a deficiency of 40%.
 • Deficiency ~ 30-45% – Large
 • Deficiency ~ 45-60% – Serious
 • Deficiency ~ >60% – Disastrous
 Annual rainfall < Average Annual Rainfall – Bad
(Subnormal) Year
 Annual rainfall ~ Average Annual Rainfall – Normal
Year
 Annual rainfall > Average Annual Rainfall – Good
Year