BASIC OF HYDROLOGY

Evaporation • Condensation • Precipitation • Surface Runoff • Interception • Transpiration • Infiltration • Sub-surface Runoff INVOLVING PROCESSES HYDROLOGICAL CYCLE CONCEPT OF HYDROLOGY BASIC OF HYDROLOGY THE EFFECT OF SOILS USE TOWARD HYDROLOGICAL CYCLE water balance THE HYDROLOGY CONTINUITY EQUATION calculate

CONCEPT OF HYDROLOGY • Discusses the hydrologic cycle, it’s processes, water balance, precipitation types, estimation of precipitation, and analysis of precipitation data. Also methods of measurement of stream flow, stage discharge relation, unit hydrograph theory, Transposition of Hydrograph, Synthesis of hydrograph from basin characteristics, stream flow routing, flood frequency analysis and attenuation of flood flows. Emphasis is given towards the calculation of rain fall data and urban drainage concept in developing new areas.

What Is Hydrology? • The study of water on, under, and over the Earth’s surface, and from its origins to all its destinations on the earth is called hydrology. • The scientific study of water, seeking to explain the water balance equation in terms of time and space, and assessing the impact of physical and chemical processes and their role in ecosystems.

Uses of Engineering Hydrology • Hydrology is used to find out maximum probable flood at proposed sites e.g. Dams. • The variation of water production from catchments can be calculated and described by hydrology. • Engineering hydrology enables us to find out the relationship between a catchment’s surface water and groundwater resources • The expected flood flows over a spillway, at a highway Culvert, or in an urban storm drainage system can be known by this very subject. • It helps us to know the required reservoir capacity to assure adequate water for irrigation or municipal water supply in droughts condition. • It tells us 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 • Used in connection with design and operations of hydraulic structure • Used in prediction of flood over a spillway, at highway culvert or in urban storm drainage • Used to assess the reservoir capacity required to assure adequate water for irrigation or municipal water supply during drought • Hydrology is an indispensable tool in planning and building hydraulic structures. • Hydrology is used for city water supply design which is based on catchments area, amount of rainfall, dry period, storage capacity, runoff evaporation and transpiration.

HYDROLOGY Surface Water Hydrology Ground Water Hydrology Ice and Snow Hydrology Limnology Hydrology Branches of Hydrology

Hydrological Cycle

Hydrological Cycle • The hydrologic cycle is the continuous, unsteady circulation of water from the atmosphere to and under the land surface and back to the atmosphere by various processes. It is dynamic in that the quantity and quality of water at a particular location may vary greatly with time. Temporal variations may occur in the atmosphere, on land surface, in surface waters, and in the groundwater of an area. Within the hydrologic cycle, water may appear in all three of its states; solid, liquid, and gas.

Solar energy heats up the oceans water surface, lake, river etc. Water falls as rain, snow Water vapour condenses into clouds Some of rain infiltrates in soil Water evaporates and rises into the air Water returns to the sea Surface runoff makes its way into rivers and streams. Rivers flow back into the ocean due to the force of gravity. The cycle starts all over again. How The Water Cycle Works

Evaporation • Evaporation is the process by which water is converted from its liquid form to its vapor form and thus transferred from land and water masses to the atmosphere. • The rate of evaporation depends upon: • Wind speed: the higher the wind speed, the more evaporation • Temperature: the higher the temperature, the more evaporation • Humidity: the lower the humidity, the more evaporation

Evapotranspiration

Condensation The change of water from its gaseous form (water vapor) into liquid water. Condensation generally occurs in the atmosphere when warm air raises, cools and looses its capacity to hold water vapor. As a result, excess water vapor condenses to form cloud droplets.

Precipitation • Precipitation occurs when so much water has condensed that the air cannot hold it anymore. The clouds get heavy and water falls back to the earth in the form of rain, hail, sleet or snow. • Precipitation can occur primarily as rain. Annual amounts of precipitation are unpredictable and variable, ranging from approximately 1500 mm to 4000 mm in various locations in Malaysia. In essence, precipitation is the most important process in the hydrologic cycle because it is the 'driving force' providing water that must be accommodated in the urban environment.

Surface runoff • Sometimes referred to as overland flow, is the process whereby water moves from the ground surface to a waterway or water body. Urbanisation usually dramatically increase surface runoff volume and rates.

Interception • Interception is the amount of precipitation that wets and adheres to aboveground objects (primarily vegetation) until it is evaporated back into the atmosphere. The annual amount of interception in a particular area is affected by factors such as the amount and type of precipitation, the extent and type of vegetation, and winds. Interception is not likely to be an important process in urban stormwater management programs.

Transpiration • When plants absorb water from the ground and exhale it into the air as water vapour (Pielou, 1998). • Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves. Transpiration also includes a process called guttation, which is the loss of water in liquid form from the uninjured leaf or stem of the plant, principally through water stomata.

Environmental factors that affect the rate of transpiration: 1. LightPlants transpire more rapidly in the light than in the dark. This is largely because light stimulates the opening of the stomata (mechanism). Light also speeds up transpiration by warming the leaf. 2. TemperaturePlants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. At 30°C, a leaf may transpire three times as fast as it does at 20°C. 3. HumidityThe rate of diffusion of any substance increases as the difference in concentration of the substances in the two regions increases.When the surrounding air is dry, diffusion of water out of the leaf goes on more rapidly. 4. WindWhen there is no breeze, the air surrounding a leaf becomes increasingly humid thus reducing the rate of transpiration. When a breeze is present, the humid air is carried away and replaced by drier air. 5. Soil waterA plant cannot continue to transpire rapidly if its water loss is not made up by replacement from the soil. When absorption of water by the roots fails to keep up with the rate of transpiration, loss of turgor occurs, and the stomata close. This immediately reduces the rate of transpiration (as well as of photosynthesis). If the loss of turgor extends to the rest of the leaf and stem, the plant wilts.

Infiltration • Infiltration is defined as the passage of water through the air-soil interface. Infiltration rates are affected by factors such as time since the rainfall event started, soil porosity and permeability, antecedent soil moisture conditions, and presence of vegetation. Infiltration is a very important process in urban stormwater management and, therefore, essentially all hydrologic methods explicitly account for infiltration. Urbanisation usually decreases infiltration with a resulting increase in runoff volume and discharge.

Sub-surface runoff. • Interflow, sometimes referred to as subsurface stormflow, is the process whereby water moves laterally beneath the land surface, but above the groundwater table. Interflow occurs until water enters a waterway or water body, or is evapotranspired. Interflow is affected by the same factors as those for surface runoff. Interflow is rarely explicitly analysed; it is usually considered part of the surface runoff. Surface runoff, interflow, and precipitation falling directly on water bodies are sometimes lumped together and called direct runoff.

Example :(Jun 2012) • Explain three process involved. (CLO1:C2) i. Precipitation (2 marks) ii. Surface runoff (2 marks) iii. Evaporation (2 marks)

The Effect of Soils Use Toward Hydrological Cycle. • When development occurs, the resultant alterations to the land can lead to dramatics changes to the hydrology or the way water is transported and stored, • Impervious man-made surfaces (asphalt, concrete, rooftops) and compacted earth associated with development create a barrier to percolation of rainfall into the soil, increasing surface runoff and decreasing ground water infiltration.

This disruption of the natural water cycle leads to a number of changes, including: • Increased volume and velocity of runoff • Increased frequency and severity of flooding • Peak (storm) flows many times greater than in natural basins • Loss of natural runoff storage capacity in vegetation, wetlands, and soil • Reduced groundwater recharge • Decreased base flow (the ground water contribution to stream flow). This can result in streams becoming intermittent or dry, and also affects water temperature. Impacts on Stream Form and Function

Relationships between impervious cover and surface runoff • Natural Ground Cover • 0% Impervious Surface • Low Density Residential • 10%-20% Impervious Surface • Urban Residential • 35%-50% Impervious Surface • Commercial Industrial • 75%-100% Impervious Surface

The Effect of Soils Use Toward Hydrological Cycle. Rainwater runs off the land into water bodies. It also percolates into the soil. Percolation recharges groundwater and filters pollutants. Through both pathways, water makes its way into our creeks, ponds, wetlands, rivers, and oceans. Development puts impervious surfaces, roads, sidewalk, and roofs, that prevent percolation. Most of the rainwater runs off the land carrying pollutants into water bodies. Without percolation, flooding is more frequent and severe.

Example : (Jun 2012) Explain the effects of hydrological cycle due to the deforestation based on Figure 1( c ) below. (CLO1 : C5) precipitation river Cut-off trees

THE HYDROLOGY CONTINUITY EQUATION Inflow – Outflow = Change in Storage I – O = ds/dt I – O = ∆S P – DRO – E – T- G = ∆S @ P – ( R + ET + G) = ∆S Abbreviations: G = Ground water P = PrecipitationR = Runoff or excess rainfall DRO = direct runoffB = Subsurface flowI = InfiltrationET = EvapotranspirationE = Evaporation T = TranspirationS = Change in storage in the saturated zone - soil or groundwater

Exercise 1: • Kelantan's river catchment's expected to accept rain as much as 350 mm from the beginning October 2003 to December 2003. Evaporation and infiltration respectively was estimated at 35 mm and 25 mm in that time period. The catchment’s area was 90 km2. There is a reservoir in these catchments. Estimate runoff volume in m3 if level of reservoir unchanged.

Exercise 2: • Hydrology record for a catchment's as wide as 500 km2 show excess rainfall annual and average the surface runoff annual respectively was 90 cm and 33 cm. One reservoir as wide 1700 km2 had planned the construction in the outlet part of catchment area. The annual evaporation average to that reservoir was expected as much as 150 mm. Determine storage values that occur in that reservoir.

Exercise 3: • In period three months, Ketereh district are expected to receive rain as much as 245 mm. evapotranspiration were estimate as 80 mm and diffusion to sub surface as much as 20 mm. Wide of basin was 36 km2. Estimate : • Excess rain depth • Calculate direct runoff volume • If direct runoff may be stored in a reservoir, determine population of people which can accept water supply for now if per-capita daily utilizability was 200 liters.

Exercise 4: • Catchment area in Kuala Krai has area 1720 km2. Annual average rainfall data is 3200 mm. There are two rivers which flowed to that catchment area, namely Sungai Kuala Nal and Sungai Krai. Discharge from Sungai Kuala Nal is 23m3/s while data from Sungai Krai not obtained. Record that made to show loss result condensation process and bypass is 12% from average annual rainfall. Calculate discharge value for Sungai Krai.

Example: • In 2 months, Sungai Melaka is predicted to receive about 360mm rainfall. Evaporation is approximately 87mm and infiltration to sub layer predicted is 50mm. What is the volume of runoff in m3 if the catchment area is 80km2.

References: • http://arrowsmithwatersheds.org/links/Definitions.html • http://www.bbc.co.uk/schools/ks2bitesize/science/materials/changing_states/read5.shtml • http://www.planningwithpower.org/pubs/id-257.htm • http://lincoln.ne.gov/city/pworks/watrshed/educate/runoff/index.htm

BASIC OF HYDROLOGY