Rainfall Analysis for Yamalur watershed

We had
good rainfall (1000mm plus on an average) in 2015. Yet, this summer was harsh
for everyone. Would it have helped if we had harvested rainwater? The primary analysis
from the project area (Yamalur watershed) observes that there is enough water
available for everyone if we do rainwater harvesting leaving excess water to go
to the lakes and/or groundwater recharge.  

A watershed is
the area of land where all of the water that falls in it and drains off of it
goes to a common outlet. Biome Trust has been involved in an action research
project called Particpatory Groundwater Mapping in a Yamalur watershed of an
area 33.81 sq.km.

Now if we
overlap the watershed area over a Google map and the administrative boundary
map i.e. BBMP ward map; we would see overlaps with the existing BBMP wards.
This helped us in understanding that this watershed consists of 6 BBMP wards-
HAL Airport, Bellandur, Marathahalli, HSR layout, Singasandra, Begur, Mangmanapalya
and some non-BBMP region still under village Panchayats viz. 4 villages in Halanayakanahalli Gram Panchayat
(Halanayakanahalli, Chikkanalli, Chikkanayakanahalli, Hadosiddapura),
Rayasandra, Choodasandra, Kodathi.

Rainfall data
is very critical for it gives an idea of water falling in an area (inflow), how
much is percolating, evaporation percentage, etc. The rainfall related data
collection involved contacting Karnataka State Natural Disaster Monitoring
Center (KSNDMC). KSNDMC has installed raingauges in 89 BBMP wards so far and
almost all village panchayats have these raingauges. We managed to get 2015
rainfall data (daily and monthly) from KSNDMC except Mangmanapalya (where there
is no raingauge and so have used closest ward Bommanahalli for the analysis)
and villages Rayasandra, Choodasandra, Kodathi. We’ll keep collecting this
information. However, some primary analysis throws some interesting results:

Raw data from
KSNDMC:

Month	HAL Airport	Bellandur	Marathahalli	HSR Layout	Bommanahalli	Singasandra	Begur	Halanayakanahalli GP
Jan	3	0	3	2.5	3	2	5.5	24
Feb	0	0	0	0	0	0	0	0
Mar	42.5	43.5	44	36.5	45	77.5	16.5	0
Apr	185	118.5	128.5	139.5	129	127.5	102.5	111.5
May	100	64.5	75	102	92	78	100.5	73.5
June	105	132.5	103.5	77	83.5	96.5	100	120.0
July	68.5	55.5	59	58	58	49.5	47.5	55.5
Aug	131.5	187	96.5	169.5	186.5	184.5	138	186.5
Sep	175.5	210.5	164.5	163.5	137.5	175	175	171.5
Oct	144	148	170.5	121	80	117.5	105	160.0
Nov	269.5	200.5	186.5	215.5	229	182.5	171	201.5
Dec	7.5	7.5	3.5	3	3	7	9.62	9.5
Total	1232	1168	1034.5	1088	1046.5	1097.5	971.12	1113.5

Some quick
observations:

Based on this
data, we want to understand some more details:

·        
Runoff available- Based on the land use understanding
this information would be easy to obtain

·        
Recharge- how much of the runoff can be used for
recharge, how many wells would be essential

·        
Recharge and borewell yields- to determine the
efficiency of shallow groundwater recharge and correlation with borewell yields
(if any). So we are collecting Static water level (SWL) data from many
borewells in the watershed. We use manual
and automatic
sensors to facilitate the data collection

·        
Spatial distribution of rainfall- Bangalore
rainfall is varying at the spatial scale so understanding which areas are the
high rainfall/low rainfall would help 

·        
Microwatershed level rainfall analysis. This
yamalur watershed consists of 8 micro-watersheds

We are still
learning to analyze this data and would like to hear from you on how best to
put this data to use. We would also like to use better visualization. This is what the Participatory Groundwater mapping action
research project is attempting to do.