ES 337 Water for Developing Countries Part B

ES 337 Water for Developing Countries Part B: Irrigation and Hydropower

Brett Martinson Office F 334 Office hours Monday 11: 00 – 13: 00 Phone 22339 E-mail dbm@eng. warwick. ac. uk

Objectives • To illustrate the combination of economics, engineering and social organisation that determines the best choice between competing technologies for any specific site. • To familiarise students with the design processes and the trade-offs required in selecting sites and system components for Hydropower. • To enable students to design simple irrigation systems and choose between competing methods of water extraction. • To introduce them to the complexity of the sociotechnical interactions that constrain the construction of new irrigation or hydropower schemes.

Syllabus • B 1. Basics – Hydrology, Water conveyance, Water storage • B 2. Hydro power – Hydro systems, power needs, power available, yields and economics – system design, entry arrangements, penstocks and surge control, turbine selection, exit arrangements and draft tubes, electronics and control • B 3. Irrigation – Water needs, Irrigation types,

Books Massey, B (1998) Mechanics of Fluids Stanley Thornes (QC 211 M 2) Harvey A et al (1993) Micro-hydro Design Manual, IT Pubs, (TK 1081 H 2) Inversin, A ( 1986) Micro-Hydro Sourcebook, NRECA (TK 1081 I 6) Tong Jiandong et al (1997) Mini Hydropower, Wiley, (TK 1081 M 4) Stern, P (1997) Small Scale Irrigation IT Pubs (TC 805 S 8) Cornish G (1998) Modern Irrigation Technologies, IT Pubs, (qto TC 805. C 6) Diemer G & Huibers F (1996) Crops, People & Irrigation IT Pubs (S 613 C 7)

Web resources Course site www 2. warwick. ac. uk/fac/sci/eng/staff/dbm/es 337/ Dams World Commission on Dams (home of Dams and Development: A New Framework for Decision-Making) http: //www. dams. org Hydro www. microhydropower. net Irrigation FAO Irrigation Water Management Training Manuals www. fao. org/docrep/

Assessment • Exam (70%) – Three of six questions (choose four) • Assessed work (30%) – Set in week 14 – Worth 2. 25 CATS ( 22 ½ hours work)

Part B 1: Basics B 1. 1 Hydrology

B 1. 1 Hydrology Topics • Catchments • Runoff coefficient – Infiltration, rainfall runoff relations, runoff coefficients • Interpolating rainfall data – Arithmetic mean method, Thiessen networks, isohyets • Flow measurement – Buckets, staff gauge, weirs, current meters, salt gulp, float method • Flow frequency

B 1. 1. 1 Hydrology Catchments

B 1. 1. 1 Hydrology Catchments: Estimating area: Counting squares

B 1. 1. 1 Hydrology Catchments: Estimating area: Blocking

B 1. 1. 2 Hydrology Runoff: Components

B 1. 1. 2 Hydrology Runoff: Components Transpiration Evaporation Soil water Overland flow Interflow Groundwater accreditation Evapotranspiration Direct runoff

B 1. 1. 2 Hydrology Runoff: Components • Transpiration – Water used by plants and returned to the atmosphere • Evaporation – Water evaporated directly from surface puddles • Soil water – Water retained by the soil • Overland flow – water running on the surface • Interflow – Water flowing underground but feeding the water course • Groundwater accreditation – Water lost to groundwater

B 1. 1. 2 Hydrology Runoff: Infiltration

B 1. 1. 2 Hydrology Runoff: Coefficient R = Runoff (mm s-1) k = Runoff coefficient P = Precipitation (mm s-1)

B 1. 1. 2 Hydrology Runoff: Coefficients Surface Concrete or Asphalt Gravel - Compact Clay - Bare Coefficient 0. 8 -1 0. 75 Clay - Light Vegetation 0. 6 Clay - Dense Vegetation 0. 5 Gravel - Bare 0. 65 Gravel - Light Vegetation 0. 5 Gravel - Dense Vegetation 0. 4 Loam - Bare 0. 6 Loam - Light Vegetation 0. 45 Loam - Dense Vegetation 0. 35 Sand - Bare 0. 5 Sand - Light Vegetation 0. 4 Sand - Dense Vegetation 0. 3 Grass Areas 0. 35

B 1. 1. 2 Hydrology Streamflow Qstream = Stream flow (litres s-1) R = Runoff (mm s-1) A = Catchment area (m 2)

B 1. 1. 3 Hydrology Spatial interpolation of rainfall data

B 1. 1. 3 Hydrology Spatial interpolation: Arithmetic mean • Average each station in the area P = Precipitation Subscripts are station numbers

B 1. 1. 3 Hydrology Spatial interpolation: Arithmetic mean: Limitations • Quick and dirty • Takes no account of changes in rain gauge density – outlying, unrepresentative gauges can be over valued • Not applicable if rainfall is dominated by topography, intense convection or very localised rainfall

B 1. 1. 3 Hydrology Spatial interpolation

B 1. 1. 3 Hydrology Spatial interpolation: Thiessen method

B 1. 1. 3 Hydrology Spatial interpolation: Thiessen method P = Precipitation A = Area Subscripts refer to regions

B 1. 1. 3 Hydrology Spatial interpolation: Thiessen method: Limitations • Not applicable if rainfall is dominated by topography, intense convection or very localised rainfall • Can be unnecessarily time consuming as catchment becomes smaller and rain gauges are more spaced out – simple distance weighting may be adequate

B 1. 1. 3 Hydrology Spatial interpolation: Isohyets 30 mm 20 mm 10 mm

B 1. 1. 3 Hydrology Spatial interpolation: Isohyets: Limitations • Not applicable if rainfall is dominated by topography or intense convection (but better than Thiessen) • Often difficult to obtain in low-income countries and usually only for average yearly precipitation

B 1. 1. 4 Hydrology Flow estimation • Buckets • Float • Weirs • Staff gauge • Current meters • Salt gulp

B 1. 1. 4 Hydrology Flow estimation: Buckets

B 1. 1. 4 Hydrology Flow estimation: Buckets: Limitations • Only useful for flows <20 l/s • Whole flow must be channelled to the bucket

B 1. 1. 4 Hydrology Flow estimation: Float

B 1. 1. 4 Hydrology Flow estimation: Float: Limitations • Average flow can only be inferred from flow at surface • The stream bed should not have any significant changes over the test length • Needs a good approximation of the stream bed shape – which can be tedious

B 1. 1. 4 Hydrology Flow estimation: Float: Correction factors Type Correction Concrete channel, rectangular section, smooth 0. 85 Large, slow clear stream (>10 m 2) 0. 75 Small regular stream (<10 m 2), smooth bed 0. 65 Shallow (<0. 5 m) turbulent stream 0. 45 Very shallow (<0. 2 m) or rocky stream 0. 25

B 1. 1. 4 Hydrology Flow estimation: Weirs

B 1. 1. 4 Hydrology Flow estimation: Weirs: Calculation for rectangular weirs >2 h b>3 h >2 h h H

B 1. 1. 4 Hydrology Flow estimation: Weirs: Calculation: Weir coefficients for rectangular weirs Head on weir h/H 0. 2 0. 4 0. 6 0. 8 1 2 5 0. 5 2. 31 2. 28 2. 27 2. 26 1 2. 07 2. 05 2. 04 2. 03 2 1. 95 1. 93 1. 92 1. 91 1. 90 10 1. 85 1. 83 1. 82 1. 81 ¥ 1. 83 1. 81 1. 80 1. 79

B 1. 1. 4 Hydrology Flow estimation: Weirs: Calculation for triangular weirs >2 h b >2 h h

B 1. 1. 4 Hydrology Flow estimation: Weirs: Calculation: Weir coefficients for triangular weirs 1. 39

B 1. 1. 4 Hydrology Flow estimation: Weirs: Limitations • An initial flow estimate is required to ensure the notch is an appropriate size • The weir must be perfectly sealed • Permanent weirs are costly • Even a temporary weir can be problematic and time consuming to construct

B 1. 1. 4 Hydrology Flow estimation: Staff gauge

B 1. 1. 4 Hydrology Flow estimation: Staff gauge: Limitations • Needs a good approximation of the stream bed shape which must remain valid – erosion/siltation will effect the validity of measurements • Only valid for comparing flows over time – an initial flow reading must be taken by another method • “weir coefficients” will change with water height

B 1. 1. 4 Hydrology Flow estimation: Current meters

B 1. 1. 4 Hydrology Flow estimation: Current meters: Limitations • Needs a good approximation of the stream bed shape • Cost? • Fragility?

B 1. 1. 4 Hydrology Flow estimation: Salt gulp

B 1. 1. 4 Hydrology Flow estimation: Salt gulp: Problems

B 1. 1. 4 Hydrology Flow estimation: Salt gulp: Limitations • Automated equipment can be expensive – non automated procedure is complex • Needs skill to take readings and interpret duff ones • Errors may not be apparent unless maths is done on-site

B 1. 1. 5 Hydrology Flow frequency: Time series

B 1. 1. 5 Hydrology Flow frequency: Mass curve (Rippl diagram)

B 1. 1. 5 Hydrology Flow frequency: Buckets

B 1. 1. 5 Hydrology Flow frequency: Exceedance (flow duration curve) Daily Rainfall (mm) Occurrences (frequency) Cumulative frequency Percentage cumulative frequency 100 0 0 0. 0% 99 0 0 0. 0% 98 1 1 0. 1% 97 0 1 0. 1% . . 10 44 710 52. 5% 9 52 762 56. 4% 8 54 816 60. 4% 7 90 906 67. 0% 6 78 984 72. 8% 5 126 1110 82. 1% 4 106 1216 89. 9% 3 96 1312 97. 0% 2 39 1351 99. 9% 1 1 1352 100. 0%

B 1. 1. 5 Hydrology Flow frequency: Exceedance (flow duration curve) http: //www. geocities. com/jonpeltier/Excel/Charts/Probability. Chart. html

B 1. 1 Hydrology Summary 1. Streams are defined by their “catchments”; the area where rain falls and flows to the stream 2. Rainfall over a catchment can be converted to a (fairly rough) estimate of streamflow by using a runoff coefficient 3. Nearby rain gauges can be used to give an estimate of the rainfall over a catchment using arithmetic mean or Thiessen methods. Isohyets can also be used 4. Streamflow can also be measured directly using means of buckets, floats, weirs, staff gauges current meters and the salt gulp technique 5. Time series data can usefully be summarised as a mass curve or as an exceedance

B 1. 2 Next…. . Water Storage