![37
(iii). The water balance equation can be arranged to produce:
ET+F= P - R - ΔS
where:
P = (1.3 2500106)
= 3.25109 m3
R = 9.4608108 m3 (from [i])
ΔS = 0 (i.e. no change in storage)
So,
ET + F = 3.25109 - 9.4608108
= 2.30392109 m3
= (2.30392109) / (2500106)
= 0.92 m
Problem #1](https://image.slidesharecdn.com/1-2-hydrologiccycle-241012053718-3af6459c/85/Hydrological-cycle-topic-in-Hydrology-engineering-subject-37-320.jpg)
Hydrological cycle topic in Hydrology engineering subject
- 1. Dr. Mujahid Khan, UET Peshawar Hydrology and Water Management
- 2. 2 Course Outline • Hydrologic Cycle and its Processes • Water Balance Approach • Estimation and Analysis of Precipitation Data • Infiltration and Runoff Phenomena • Application of TR55 model for Runoff Estimation • Measurement of Stream Flow and Stage Discharge Relationships • Unit Hydrograph Theory and its Application • Flood Flow Routing and its Application • Frequency Analysis • Application of HEC-HMS model
- 3. 3 The study of water, including rain, snow and water on the earth’s surface, covering its properties, distribution, utilisation, etc. (Chambers Science and Technology Dictionary) The study of water in all its forms, and from its origins to all its destinations on the earth. (Bras, 1990) The science dealing with the waters of the earth, their occurrence, distribution and circulation, their chemical and physical properties, and their interaction with the environment. (Ward & Robinson, 1999) HYDROLOGY
- 4. 4 Main Branches HYDROLOGY Ground Water Hydrology Surface Water Hydrology
- 5. 5 Water is one of the most valuable natural resources essential for human and animal life, industry and agriculture. The study of hydrology helps us to know (i) The maximum probable flood that may occur at a given site and its frequency; this is required for the safe design of drains and culverts, dams and reservoirs, channels and other flood control structures. (ii) The water yield from a basin—its occurrence, quantity and frequency, etc. this is necessary for the design of dams, municipal water supply, water power, river navigation, etc. (iii)The ground water development for which a knowledge of the hydrogeology of the area, i.e., of the formation soil, recharge facilities like streams and reservoirs, rainfall pattern, climate, cropping pattern, etc. are required. (iv)The maximum intensity of storm and its frequency for the design of a drainage project in the area. Scope of Hydrology
- 6. 6 Engineering Hydrology • It uses hydrologic principles in the solution of engineering problems arising from human exploitation of water resources of the earth. • The engineering Hydrologist, or water resources engineer, is involved in the planning, analysis, design, construction and operation of projects for the control, utilization and management of water resources. • Hydrologic calculations are estimates because mostly the empirical and approximate nature of methods are used to describe various hydrological processes.
- 7. 7 Quantity of water available from a catchment ? Quality of water in a catchment eg. sediment & phosphate content ? Problems Related to Hydrology
- 8. 8 Peak discharge expected in a stream during a storm ?
- 9. 9 The design of hydraulic structures eg. dams/ reservoirs, bridges
- 10. 10 Damage caused by peak floods
- 11. 11 Engineering Hydrology seeks to answer questions of the following types: • What is the maximum probable flood at a proposed dam site? • How does a catchment’s water yield vary from season to season and from year to year? • What is the relationship between a catchment’s surface water and groundwater resources? • What flood flows can be expected over a spillway, at a highway culvert, or in an urban storm drainage system? • What reservoir capacity is required to assure adequate water for irrigation or municipal water supply in droughts condition? • What hydrologic hardware (e.g. rain gauges, stream gauges etc) and software (computer models) are needed for real-time flood forecasting? Uses of Engineering Hydrology
- 12. 12 • In seeking answers to these questions, Engineering Hydrology uses various Measurement and Analysis techniques. • Hydrological Measurements Deals with the measurement of water in the different phases of hydrological cycle such as rainfall and stream gauging. • Hydrological Analysis Aims to develop a methodology to quantify a certain phase or phases of hydrologic cycle – for instance, precipitation, infiltration, or surface runoff. Hydrologic Measurement and Analysis
- 13. 13 HYDROLOGIC CYCLE • The hydrologic cycle describes the continues re-circulating transport of the waters of the earth, linking atmosphere, land and oceans. • To explain it briefly, water evaporates from the ocean surface, driven by energy from the Sun, and joins the atmosphere, moving inland as clouds. Once inland, atmospheric conditions act to condense and precipitate water onto the land surface, where, driven by gravitational forces, it returns to the ocean through river and streams. • The process is quite complex, containing many sub-cycles. • Engineering Hydrology takes a quantitative view of the hydrologic cycle.
- 14. 14
- 16. 16 • The quantification of the hydrologic cycle which is an open system, can be represented by a mass balance equation, where inputs minus outputs are equal to the change in storage. I - O = DS It is a basic Hydrologic Principle or equation that may be applied either on global or regional scale. • The water holding elements of the hydrological cycle are: 1. Atmosphere 2. Vegetation 3. Snow packs 4. Land surface 5. Soil 6. Streams, lakes and rivers 7. Aquifers 8 Oceans Hydrologic Cycle
- 17. 17 Hydrological Processes • Precipitation • Interception • Evaporation • Transpiration • Infiltration • Overland flow • Sub Surface flow (P-96) • Groundwater outflow
- 18. 18
- 19. 19 Evapotranspiration from land Evaporation from ocean Moisture over land Precipitation on land 100 61 39 424 Precipitation on ocean 385 Groundwater outflow Surface outflow 38 1 Surface flow Groundwater flow Infiltration Global Water Balance of The hydrological cycle
- 20. 20 In the atmosphere: Precipitation (P) = Evapotranspiration (ET) 100+385 = 61+424 On land: P = Evapotranspiration (ET) + Surface runoff (R) + Groundwater outflow 100 = 61 + 38 + 1 Over oceans and seas: Ocean precipitation + Surface runoff + Groundwater outflow = Evaporation (E) 385 + 38 + 1 = 424 Global Water Balance
- 21. 21 Table 1. Estimated Distribution of World's Water. Component Volume 1000 km3 % of Total Water Atmospheric water 13 0.001 Surface Water Salt Water in Oceans Salt water in lakes & inland seas Fresh water in lakes Fresh water in stream channels Fresh water in glaciers and icecaps Water in the biomass 1320000 104 125 1.25 29000 50 97.2 0.008 0.009 0.0001 2.15 0.004 Subsurface water Vadose water G/W within depth of 0.8 km G/W between 0.8 and 4 km depth 67 4200 4200 0.005 0.31 0.31 Total (rounded) 1360000 100
- 22. 22 Hydrologic Systems • Chow, Maidment, and Mays (1988) defined a hydrologic system as a structure or volume in space, surrounded by a boundary, that accepts water and other inputs, operates on them internally, and produces them as outputs. • The structure (for surface or subsurface flow) or volume in space (for atmospheric moisture flow) is the totality of the flow paths through which the water may pass as throughout from the point it enters the system to the point it leaves. • The boundary is a continuous surface defined in three dimensions enclosing the volume or structure. • A working medium enters the system as input, interacts with the structure and other media, and leaves as output. • Physical, chemical and biological processes operate on the working media within the system; the most common working media involved in hydrologic analysis are water, air and heat energy.
- 23. 23 Mass Balance in Hydrologic Systems • General form: Rate of accumulation of mass in system = Input rate - output rate ± reaction • Hydrologists: Change in storage = Inflow – Outflow • Assumptions: – no reaction – volume, pressure, temperature do not change
- 24. 24 Inflow: 1. Precipitation 2. Import defined as water channeled into a given area. 3. Groundwater inflow from adjoining areas. Outflow: 1. Surface runoff outflow 2. Export defined as water channeled out of the same area. 3. Evaporation 4. Transpiration 5. Interception Change in Storage: This occurs as change in: 1. Groundwater 2. Soil moisture 3. Surface reservoir water and depression storage 4. Detention Storage Water Balance Components
- 25. 25 Global Hydrologic Cycle • The global hydrologic cycle can be represented as a system containing three subsystems: the atmospheric water system, the surface water system, and the subsurface water system. • Block-diagram (flow chart) representation of GHC is shown in Figure#1.
- 26. 26 Precipitation Infiltration Transpiration Interception Groundwater recharge Overland flow Subsurface flow Runoff to streams and ocean Surface runoff Groundwater flow Evaporation Atmospheric Water Subsurface Water Surface Water Block-diagram representation of the global hydrologic system (Chow et al. 1988).
- 27. 27 Regional Water Balance (Water Budget) Precipitation (P) Evapotranspiration (ET) Surface runoff (R) Infiltration (F) A mass balance over time from t = 0 to T, i.e. Inputs - Outputs = Change in Storage P - (R+ET+F) = ΔS All terms in the hydrologic equation should be in the same units.
- 28. 28 Infiltration (F) Storage (S) Time t = 0 Time t = T Change in storage (DS) Precipitation (P) Evapotranspiration (ET) Surface runoff (R) Schematic representation of the mass balance equation DS = P - (R + F + ET) DS = +ve if P > (R + F + ET) DS = -ve if P < (R + F + ET) DS = 0 if P = (R + F + ET)
- 29. 29 Catchment and Basin • A catchment is a portion of the earth’s surface that collects runoff and concentrates it at its furthest downstream point, referred to as the catchment outlet. • The runoff concentrated by a catchment flows either into a larger catchment or into the ocean. • The place where a stream enters a larger stream or body of water is referred to as the mouth. • The terms watershed and basin are commonly used to refer to catchments. Generally, watershed is used to describe a small catchment (stream watershed), whereas basin is reserved for large catchments (river basins).
- 30. 30 • The watershed or basin is defined by the surrounding topography, the perimeter of which is called a divide. • It is the highest elevation surrounding the watershed. • All of the water that falls on the inside of the divide has the potential to be shed into the streams of the basin encompassed by the divide. Water falling outside of the divide is shed to another basin. • The water flowing in streams is called stream flow. Watershed and Stream
- 31. 31 • Horton suggested a classification of stream order as a measure of the amount of branching within a basin. • A first order stream is a small, unbranched tributary. • A second order stream has only first order tributaries. • A third order stream has first and second order tributaries and so on. • When a channel of lower order joins a channel of higher order, the channel downstream retains the higher of the two orders. Stream Order
- 32. 32 Figure 1. Stream Orders of a Watershed. Divide 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 1 2 3 3 3 4 4 2 1 1
- 33. 33 Watershed Characteristics Size Slope Shape Soil type Storage capacity Reservoir Divide Natural stream Urban Concrete channel
- 34. 34 For the analysis and design of any hydrologic project adequate data and length of records are necessary. A hydrologist is often posed with lack of adequate data. The basic hydrological data required are: (i) Climatological data (ii) Hydrometeorological data like temperature, wind velocity, humidity, etc. (iii) Precipitation records (iv) Stream-flow records (v) Seasonal fluctuation of ground water table or piezometric heads (vi) Evaporation data (vii) Cropping pattern, crops and their consumptive use (viii) Water quality data of surface streams and ground water (ix) Geomorphologic studies of the basin, like area, shape and slope of the basin, mean and median elevation, mean temperature (as well as highest and lowest temperature recorded) and other physiographic characteristics of the basin; stream density and drainage density; tanks and reservoirs (x) Hydrometeorological characteristics of basin: i. (Depth-area-duration (DAD) curves for critical storms (station equipped with self-recording raingauges). ii. Isohyetal maps—Isohyets may be drawn for long-term average, annual and monthly precipitation for individual years and months iii. Cropping pattern—crops and their seasons iv. Daily, monthly and annual evaporation from water surfaces in the basin v. Water balance studies of the basin vi. Soil conservation and methods of flood control HYDROLOGICAL DATA
- 35. 35 In a given year, a catchment with an area of 2500 km2 received 1.3 m of precipitation. The average rate of flow measured in a river draining the catchment was 30 m3s-1. (i). How much total river runoff occurred in the year (in m3)? (ii). What is the runoff coefficient? (iii).How much water is lost due to the combined effects of evaporation, transpiration, and infiltration. (Express in m). Problem #1
- 36. 36 Solution (i). Total runoff volume = number of seconds in a year average flow rate = 31 536 000 30 = 9.4608108 m3 (ii). Runoff coefficient = runoff volume/ precipitation volume = (9.4608108) / (1.3 2500 106) = 0.29 (29 %) Problem #1
- 37. 37 (iii). The water balance equation can be arranged to produce: ET+F= P - R - ΔS where: P = (1.3 2500106) = 3.25109 m3 R = 9.4608108 m3 (from [i]) ΔS = 0 (i.e. no change in storage) So, ET + F = 3.25109 - 9.4608108 = 2.30392109 m3 = (2.30392109) / (2500106) = 0.92 m Problem #1
- 38. 38 In a given year, a catchment with an area of 1750 km2 received 1250 mm of precipitation. The average rate of flow measured in a river draining the catchment was 25 m3s-1. (i). Calculate how much total river runoff occurred in the year (in m3). (ii).Calculate the runoff coefficient. What is the percentage runoff ? Problem #2 Area of the catchment = 1750 km2 = 1750 x 10^6 m2 Flow rate in the river = 25 m3/s Precipitation received = 1250 mm = 1.25 m
- 39. 39 Solution: Total runoff volume = 31 536 000 x 25 = 788.4 x 10^6 m3 Total annual precipitation = (1.25) x (1750 x 10^6) = 2187.5 x 10^6 m3 Flow rate during the year = 2187.5 x 10^6 / (365 x 24 x 60 x 60) = 69.36 m3/s Runoff Coefficient = Actual flow in river / Total precipitation occurred = 25 / 69.36 = 0.36 Percentage of flow = 0.36 x 100 = 36% Problem #2
- 40. 40 Problem #3 A lake has a surface area of 708,000 m2. In May, the River A flows into the lake at an average rate of 1.5 m3/s. River B flows out of lake at an average rate of 1.25 m3/s. The evaporation rate was measured as 14.0 cm/month. A total of 22.5 cm of precipitation fell in May. Seepage losses are negligible. The average depth in the lake on May 1 was 19 m. What was the average depth on May 30th? • Surface area of lake = A = 708,000 m2 • Average depth on May 1 = 19 m
- 41. 41 • Inputs to the lake Average inflow = I = 1.5 m3/s = 3,888,000 m3/mo Precipitation = P = 22.5 cm/month = 159,300 m3/mo • Outputs to the lake Average outflow = O = 1.25 m3/s = 3,240,000 m3/mo Evaporation = E = 14.0 cm/month = 99,300 m3/mo Seepage = 0 Problem #3 Mass Balance equation: Change in volume of water in the lake during this month = DS = change in storage = Inflow - Outflow + Precipitation - Evaporation
- 42. 42 • DS = I – O + P – E = = 3,888,000 m3/mo – 3,240,000 m3/mo + 159,300 m3/mo – 99,300 m3/mo • DS = 708,000 m3/mo Problem #3 • Since DS = 708,000 m3/mo and the average surface area is 708,000 m2, the change in depth during the month = (708,000 m3/mo)/708,000 m2 = 1 m or about 3.25 ft. • Note DS is positive, this means that the volume increases and therefore the depth increases. The new average depth on May 30th would be 20 m.