MyWatershed -Water Balance Exercise What will happen if we build a - PowerPoint PPT Presentation

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

Regional Picture Village Ghotewadi Crop Choice Total Land 3000 Ha. What is a feasible cropping Forest 1200 Ha. pattern? Commons 100 Ha. Wastelands 300 Ha. Is ( � i A i r i ) − ( A ∗ f ) positive? Agricultural 1500 Ha. But what is A ? Rainfall ( f ) 520mm Crop Area A i (Ha.) Req. r i (mm) Season Grapes 100 1200 Annual Soyabean 300 500 Kharif Maize 200 700 Kharif Tomato 200 650 Summer () July 24, 2017 24 / 37

ET load graphically critical critical Rain point 1 point 2 Kharif Rabbi Summer Long Annual S O N D M A M J J A J F J Run−Off () July 31, 2017 27 / 39

Rains () July 24, 2017 25 / 37

Demand () July 24, 2017 26 / 37

Deficit () July 24, 2017 27 / 37

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. () July 24, 2017 28 / 37

Rainfall Mean Annual Precipitation (1961 - 1990) 0° 150° w.G. 120° 90° 60° 30° 30° 60° 90° 120° 150° e.G. 180° 60° 60° 30° 30° 0° 0° 30° 30° 60° 60° Scale 1 : 120 000 000 Precipitation in mm/a Source: Gridded Precipitation Normals Data Set, Global Precipitation Climatology Centre (GPCC), 0 10 50 100 200 500 1000 2500 no data Offenbach 2007 source: whymap.org , BGR-Unesco. () July 24, 2017 29 / 37

Run-off () July 24, 2017 30 / 37

A Basin () July 24, 2017 31 / 37

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? () July 31, 2017 35 / 39

Recharge Groundwater Recharge (1961 - 1990) per Capita (2000) 150° 120° 90° 60° 30° 0° 30° 60° 90° 120° 150° e.G. 180° 60° 60° 30° 30° 0° 0° 30° 30° 60° 60° Scale 1 : 120 000 000 Groundwater recharge in m 3 /person*a Sources: Mean groundwater recharge calculated with WaterGAP 2.1, Universities of Frankfurt & Kassel 2007; country boundary Population data based on GPW - Version 3, Center for International Earth Science Information Network 0 250 500 1000 1500 3000 10000 no data (CIESIN) 2005 source: whymap.org , BGR-Unesco. () July 24, 2017 33 / 37

Recharge/Geology-India source: whymap.org , BGR-Unesco. () July 24, 2017 34 / 37

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% () July 24, 2017 35 / 37

Thanks () July 24, 2017 36 / 37

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? () August 2, 2017 2 / 25

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 Stream ������ ������ Water−Table ������ ������ ������ ������ ������ ������ Base−flow ������ ������ () August 2, 2017 3 / 25

What happens when it rains stream(t) = only-surface(t)+sometime-in-ground(t) precip(t) = infil(t)+only-surface(t) infil(t) = sometime-in-ground(t)+all-time-in-ground(t) out(t) = stream(t)+all-time-in-ground(t) precip(t) = out(t) () August 2, 2017 4 / 25

What happens when it rains Rain Infiltration Overland Baseflow Time stream(t) = only-surface(t)+sometime-in-ground(t) precip(t) = infil(t)+only-surface(t) infil(t) = sometime-in-ground(t)+all-time-in-ground(t) out(t) = stream(t)+all-time-in-ground(t) precip(t) = out(t) () August 2, 2017 5 / 25

Immediate Runoff () August 2, 2017 6 / 25

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 − α t + 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. Monsoons Runoff Baseflow Baseflow Time () August 2, 2017 7 / 25

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? () August 2, 2017 8 / 25

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. () August 2, 2017 9 / 25

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 storage i ( n + 1) = (1 − β ) ∗ storage i ( n ) + overflow i − 1 ( n ) − ∆ i ( n ) overflow i ( n + 1) = A ∗ ( f i ( n ) − b ) ∗ (1 − α ) + ∆ i ( n ) Rain f (mm) S1 S2 S3 S4 S5 Day 1 11 11 9 9 9 Day 2 0 0 0 0 0 Day 3 2 2 2 3 2 () August 2, 2017 10 / 25

Measuring Rain (wikipedia) Standard : Funnel-top, and Tipping bucket : Funnel, with water a measuring cylinder. falling on a see-saw. Pulse generated every 0.2mm. Now standard in India. () August 2, 2017 11 / 25