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ES337 Water for Developing Countries Part B: Irrigation and Hydropower

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Brett Martinson Office F334 Office hours Monday 11:00 – 13:00 Phone

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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 socio- technical interactions that constrain the construction of new irrigation or hydropower schemes.

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Syllabus B1.Basics –Hydrology, Water conveyance, Water storage B2.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 B3.Irrigation –Water needs, Irrigation types,

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Books Massey, B (1998) Mechanics of Fluids Stanley Thornes (QC 211 M2) Harvey A et al (1993) Micro-hydro Design Manual, IT Pubs, (TK 1081 H2) Inversin, A ( 1986) Micro-Hydro Sourcebook, NRECA (TK 1081 I6) Tong Jiandong et al (1997) Mini Hydropower, Wiley, (TK 1081 M4) Stern, P (1997) Small Scale Irrigation IT Pubs (TC 805 S8) Cornish G (1998) Modern Irrigation Technologies, IT Pubs, (qto TC 805.C6) Diemer G & Huibers F (1996) Crops, People & Irrigation IT Pubs (S 613 C7)

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Web resources Course site www2.warwick.ac.uk/fac/sci/eng/staff/dbm/es337/ Dams World Commission on Dams (home of Dams and Development: A New Framework for Decision-Making) Hydro Irrigation FAO Irrigation Water Management Training Manuals

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Assessment Exam (70%) –Three of six questions (choose four) Assessed work (30%) –Set in week 14 –Worth 2.25 CATS ( 22 ½ hours work)

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Part B1: Basics B1.1 Hydrology

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B1.1 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

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B1.1.1Hydrology Catchments

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B1.1.1Hydrology Catchments: Estimating area: Counting squares

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B1.1.1Hydrology Catchments: Estimating area: Blocking

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B1.1.2Hydrology Runoff:Components

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Groundwater accreditation Interflow Overland flow Evaporation Transpiration Direct runoff Evapotranspiration Soil water

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B1.1.2Hydrology 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

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B1.1.2Hydrology Runoff:Infiltration

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B1.1.2Hydrology Runoff:Coefficient R = Runoff (mm s -1 ) k = Runoff coefficient P = Precipitation (mm s -1 )

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B1.1.2Hydrology Runoff:Coefficients SurfaceCoefficient Concrete or Asphalt0.8-1 Gravel - Compact0.7 Clay - Bare0.75 Clay - Light Vegetation0.6 Clay - Dense Vegetation0.5 Gravel - Bare0.65 Gravel - Light Vegetation0.5 Gravel - Dense Vegetation0.4 Loam - Bare0.6 Loam - Light Vegetation0.45 Loam - Dense Vegetation0.35 Sand - Bare0.5 Sand - Light Vegetation0.4 Sand - Dense Vegetation0.3 Grass Areas0.35

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Q stream = Stream flow (litres s -1 ) R = Runoff (mm s -1 ) A = Catchment area (m 2 ) B1.1.2Hydrology Streamflow

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B1.1.3Hydrology Spatial interpolation of rainfall data

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P = Precipitation Subscripts are station numbers B1.1.3Hydrology Spatial interpolation: Arithmetic mean Average each station in the area

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B1.1.3Hydrology 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

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B1.1.3Hydrology Spatial interpolation

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B1.1.3Hydrology Spatial interpolation: Thiessen method

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P = Precipitation A = Area Subscripts refer to regions B1.1.3Hydrology Spatial interpolation: Thiessen method

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P = Precipitation A = Area Subscripts refer to regions

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B1.1.3Hydrology 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

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B1.1.3Hydrology Spatial interpolation: Isohyets 10mm 20mm 30mm

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B1.1.3Hydrology 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

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B1.1.4Hydrology Flow estimation Buckets Float Weirs Staff gauge Current meters Salt gulp

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B1.1.4Hydrology Flow estimation: Buckets

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B1.1.4Hydrology Flow estimation: Buckets: Limitations Only useful for flows <20l/s Whole flow must be channelled to the bucket

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B1.1.4Hydrology Flow estimation: Float

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B1.1.4Hydrology 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

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TypeCorrection Concrete channel, rectangular section, smooth 0.85 Large, slow clear stream (>10m 2 )0.75 Small regular stream (<10m 2 ), smooth bed 0.65 Shallow (<0.5m) turbulent stream0.45 Very shallow (<0.2m) or rocky stream0.25 B1.1.4Hydrology Flow estimation: Float: Correction factors

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B1.1.4Hydrology Flow estimation: Weirs

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B1.1.4Hydrology Flow estimation: Weirs: Calculation for rectangular weirs >2h b>3h h H

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B1.1.4Hydrology Flow estimation: Weirs: Calculation: Weir coefficients for rectangular weirs Head on weir h/H

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B1.1.4Hydrology Flow estimation: Weirs: Calculation for triangular weirs >2h h b

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B1.1.4Hydrology Flow estimation: Weirs: Calculation: Weir coefficients for triangular weirs 1.39

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B1.1.4Hydrology 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

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B1.1.4Hydrology Flow estimation: Staff gauge

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B1.1.4Hydrology 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

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B1.1.4Hydrology Flow estimation: Current meters

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B1.1.4Hydrology Flow estimation: Current meters: Limitations Needs a good approximation of the stream bed shape Cost? Fragility?

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B1.1.4Hydrology Flow estimation: Salt gulp

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B1.1.4Hydrology Flow estimation: Salt gulp: Problems

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B1.1.4Hydrology 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

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B1.1.5Hydrology Flow frequency: Time series

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B1.1.5Hydrology Flow frequency: Mass curve (Rippl diagram)

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B1.1.5Hydrology Flow frequency: Buckets

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B1.1.5Hydrology Flow frequency: Exceedance (flow duration curve) Daily Rainfall (mm)Occurrences (frequency) Cumulative frequency Percentage cumulative frequency % % % % % % % % % % % % % %

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B1.1.5Hydrology Flow frequency: Exceedance (flow duration curve)

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B1.1Hydrology 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

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B1.2 Next…..Water StorageNext…..Water Storage

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