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MyWatershed -Water Balance Exercise What will happen if we build a check-dam and a reservoir? Flows: Rainfall 859 mm Runoff 192 mm Evapo-transpiration 532mm Groundwater flows 135mm Stocks: Surface Water Groundwater

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MyWatershed-Water Balance Exercise

What will happen if we build a check-dam and a reservoir? Flows: Rainfall 859 mm Runoff 192 mm ↓ Evapo-transpiration 532mm Groundwater flows 135mm ↑ Stocks: Surface Water ↑ Groundwater ↑

() July 24, 2017 22 / 37

SLIDE 2

Regional Picture

Village Ghotewadi Total Land 3000 Ha. Forest 1200 Ha. Commons 100 Ha. Wastelands 300 Ha. Agricultural 1500 Ha. Rainfall (f ) 520mm

Crop Choice

What is a feasible cropping pattern? Is (

i Airi) − (A ∗ f ) positive?

But what is A? Crop Area Ai (Ha.)

Req. ri (mm)

Season Grapes 100 1200 Annual Soyabean 300 500 Kharif Maize 200 700 Kharif Tomato 200 650 Summer

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SLIDE 3

ET load graphically

J S O N J F M J J A D A M Long Kharif Rabbi Summer Annual point 1 critical critical point 2 Rain

Run−Off

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Rains

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Demand

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Deficit

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Precipitation

Precipitation is the most visible component of the Hydrological cycle. Rains in India are the most important cultural and economic event of the year. 15 wets days supply 50% of annual rains! India receives most of its rains (of about 900 mm/year average) in the form of three monsoons:

◮ South-west (for W. and C. India, May 1st-Oct. 1st) ◮ South-east (for E. and N. India, June 1st-Oct. 1st) ◮ South (south-east coast of India, Oct. 1 Dec. 1st)

Most important regional data. Observed by network of rain-guages. Daily Rainfall mm/day Season Total mm Rainfall Intensity mm/day Rainy Days No.

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Rainfall

Mean Annual Precipitation (1961 - 1990)

Scale 1 : 120 000 000

Source: Gridded Precipitation Normals Data Set, Global Precipitation Climatology Centre (GPCC), Offenbach 2007

60° 180° 150° e.G. 60° 30° 0° 120° 30° 60° 120° 150° w.G. 90° 90° 60° 30° 0° 30° 60° 30° 0° 30° 60°

Precipitation in mm/a

10 50 100 200 1000 500 2500 no data

source: whymap.org, BGR-Unesco.

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Run-off

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SLIDE 10

A Basin

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Mahanadi Basin-Data

Length of Mahanadi River (Km) 850 Catchment Area (Sq.km.) 141600 Average Water Resource Potential (MCM) 66800 Utilizable* Surface Water Resource (MCM) 50000 Total Live Storage Capacity of Projects (MCM) 14200 *-utilizable: which will not directlu run off to sea, or is available within the country’s boundary. Can you estimate the infiltration fraction? What is the use of storage? What is the connection between the two?

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Recharge

Scale 1 : 120 000 000

Sources: Mean groundwater recharge calculated with WaterGAP 2.1, Universities of Frankfurt & Kassel 2007; Population data based on GPW - Version 3, Center for International Earth Science Information Network (CIESIN) 2005

Groundwater Recharge (1961 - 1990) per Capita (2000)

country boundary

Groundwater recharge in m3/person*a

250 500 1000 1500 10000 3000 no data

60° 30° 0° 30° 60° 180° 150° e.G. 120° 90° 60° 30° 0° 30° 60° 90° 120° 150° 60° 30° 30° 0° 60°

source: whymap.org, BGR-Unesco.

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Recharge/Geology-India

source: whymap.org, BGR-Unesco.

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CGWB estimates

Annual Replenishable Ground Water Resources 433 bcm Net Annual Ground Water Availability 398 bcm Annual Ground Water Draft for Irrigation 245 bcm Domestic & Industrial uses Stage of Ground Water Development 62%

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SLIDE 15

Thanks

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SLIDE 16

What happens when it rains?

What happens when a drop hits the ground? How much flows? Where does it go? How do we measure and estimate rain and flow?

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Precipitation to Run-Off

Many stages from Precipitation to Run-Off Interception: The contact of the raindrop with vegetation. Stem-Flow: Flow of water from plant to soil. Infiltration: Coversion of liquid-water to soil moisture.

◮ Saturation: All soil pores get filled with water.

Run-Off: Two components:

◮ Overland-flow: Post saturation! Excess flow reaches streams. ◮ Base-flow: Groundwater releases moisture into streams. Run−Off Infiltration Base−flow Water−Table Stream

()

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What happens when it rains

stream(t) =

nly-surface(t)+sometime-in-ground(t)

precip(t) = infil(t)+only-surface(t) infil(t) = sometime-in-ground(t)+all-time-in-ground(t)

ut(t)

= stream(t)+all-time-in-ground(t) precip(t) =

ut(t)

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SLIDE 19

What happens when it rains

Time Rain Overland Baseflow Infiltration

stream(t) =

nly-surface(t)+sometime-in-ground(t)

precip(t) = infil(t)+only-surface(t) infil(t) = sometime-in-ground(t)+all-time-in-ground(t)

ut(t)

= stream(t)+all-time-in-ground(t) precip(t) =

ut(t)

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SLIDE 20

Immediate Runoff

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Stream-flow and Base-flow

The stream flow is largely baseflow for most of the year. Only in the monsoon is there a run-off component. A simple exponential flow model: flow = Ae−αt + B where A, B and α are parameters of the watershed. A small α signifies good health. If flow is negative, assume it to signify that the stream is dry.

Runoff Time Monsoons Baseflow Baseflow

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Infiltration and Stream-flow

Infiltration This is the part of precipitation which flows out of the watershed through rivers and streams. Overall Indian average is about 43% , in Konkan its above 93 % . The difference

◮ is stored in reservoirs and tanks. ◮ recharges ground-water. ◮ evaporates or is consumed.

Stram-flow is a function of rain-intensity, slope, land-conditions, forest-cover, existing soil-moisture and many other things. How do I estimate stream-flow and infiltration? How do I modify these?

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Slope

Both stream-flow and infiltration depend greatly on the slope. Slope-maps are an important input for developing Stream-flow and infiltration models for the water-shed. Infiltration models are easier and depend on point conditions. Stream-flow models are more difficult and also must model drainage and thus, floods. Standard models for watersheds must be developed and calibrated.

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Computing flows-A Model

Regions S1 S2 S3 S4 S5 Area Ha. 220 330 510 430 290 Capacity (TCM) 13 34 100 70 30 Storage (TCM) 2 8 12 12 20 Infiltration α 0.4 0.5 0.6 0.3 0.5 ET b (mm) 3 5 6 6 7 storagei(n + 1) = (1 − β) ∗ storagei(n) + overflowi−1(n) − ∆i(n)

verflowi(n + 1)

= A ∗ (fi(n) − b) ∗ (1 − α) + ∆i(n) Rain f (mm) S1 S2 S3 S4 S5 Day 1 11 11 9 9 9 Day 2 Day 3 2 2 2 3 2

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SLIDE 25

Measuring Rain (wikipedia)

Standard : Funnel-top, and a measuring cylinder. Tipping bucket : Funnel, with water falling on a see-saw. Pulse generated every 0.2mm. Now standard in India.

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