Hydrology 101 Gavin Fields, David Lergessner XP-LIVE webinar  This is part of our XP-LIVE educational program  Webinars have been recorded and are available at  http://www.xpsolutions.com/category/news/xplive/ Hydrology 101 Agenda  Introduction  Hydrology: The Physical Characteristics  Historic vs Design Storms  Routing Methods  Results  Direct (2D) Rainfall  Question / Answer XP Solutions  Software for modeling wastewater, stormwater, and floods  Graphical User Interface (GUI) and analytical engines  CAD/GIS type interface and data management tools  Graphical reports, maps, animations  1D analytical engine solves the complete St. Venant (Dynamic Flow) equations for gradually varied, one dimensional, unsteady flow  2D analytical engine embedded as xp2D Why Hydrology is important?  Agriculture  Planning  Stormwater  Flood / Risk  Engineering  Assessing Change Hydrologic cycle http://nd.water.usgs.gov/ukraine/english/pictures/watercycle.html Managing water means managing catchments Definition: Land bounded by natural features such as hills or mountains and from whichfromall A catchment is an area or basin of land surrounded by hills or mountains which all run-off water flows to a low point such as a stream, river or the ocean or sometimes runoff water flows to a low point. a lake. The boundary of a catchment is known as an interfluve. Roads often follow the interfluve Catchments vary in size. The Murray-Darling basin drains 1/7th of the Australian continent Indus Ganges Brahmaputra Rivers play an important role in shaping the landscape. Topographic maps help to identify slope patterns and catchment areas. Topography also plays a major role in weather and climate events. Coastal ranges have a significant impact on rainfall distribution. Rising air cools and loses its moisture Rain shadow Mountains force the winds to rise. Orographic Rainfall Port Douglas 8.30am The Outer Reef same day just over 60kms away On the western side of India, the Western Ghats cause orographic rainfall. The Himalayas to the north not only block rainbearing winds but they also deflect them to the north-west. Monsoon rains cause widespread slow onset flooding in northern Australia and parts of Asia Water running off the eastern side of the Great Dividing Range in this area will find its way into the Brisbane River System The Brisbane River is a relatively short river by world standards. Water falling on the western side of the Great Dividing Range in this area will begin a journey of hundreds of kilometres across the Australian continent. On the way the water from the river will be used in many different ways. Runoff characteristics vary from sheet flow to stream flow conditions as passing showers cross low flat areas that join river systems on the way to South Australia. Some places show evidence of river erosion yet may be dry for many years. The amount and type of vegetation cover is important and affects runoff. Rainforests are adapted to use as much water as possible. Fire can have an impact. Fire or the absence of fire can have an impact. Himalayas Deccan Just how much of the rainfall received by an area as runoff depends on a number of factors. The material on which the rain falls plays a significant role. The Indo-Gangetic Plain is composed of alluvium, which is material deposited by rivers. This material consists of silt, clay, sands and gravels. The soil and rock type affect run-off rates. In some areas the flow of water is rigidly controlled. Redcliffe 1957 Redcliffe 1987 Urbanisation affects infiltration rates Redcliffe 2014 There are many different types of floods: • flash floods which can be of natural or human origin with very little warning eg heavy rainfall in a catchment with narrow valleys or the failure of a dam or levee • rapid onset floods which rise quickly over one or two days and just as quickly fall • slow onset floods which rise over a period of days and take weeks or months to fall. Many factors affect the type of run-off and flooding which may occur. There is a time lag between the rainfall and the flood peak. This allows flood predictions to be made in distant places. Rivers such as the Barron River in north Queensland can experience very rapid changes of flow. Hydrology Overview Precipitation – losses = runoff  Precipitation    Rainfall intensity, duration, volume Snow Melt Groundwater  Losses Evapotranspiration Infiltration Depressions Storage    Hydrograph Peak flow Peak volume [Max Flow = 0.3350] Hydrology Rates  Runoff Node - Laur 0% 0 100 200 Rainfall Total Infiltration Flow 0.3 Flow (cms)    0.2 0.1 0.0 1 Wed Jan 2014 0:30 1:00 Time 1:30 Storms  Design Storms  Average intensity/ absolute depth is required  Storm duration is required  Temporal pattern is required  Historic Storms  Recorded storm events  Return period can be calculated Historic Storms  Observed rainfall:  Can be used for flood forecasting models after calibration  Can be used for validating/verifying the models Precipitation Frequency/Probability  Event Frequency  Uncertainties of nature  Result from random components  Limited historic data  Event Probability – P(E)  P(E) = n/N  Example the percent chance of occurence  10 times / 100 years = 0.1 or a 10% chance of occurrence in 100 years  Often referred to as the 10 year storm Annual Exceedance Probability  Annual Exceedance Probability (AEP) or  Average Recurrence Interval (ARI)  Risk  Mis-representation  Particularly in the Media Storage and Losses  Interception  Surface Detention  Evapotranspiration  Additional factors  Infiltration  Soil moisture storage  Groundwater  Depression storage   Infiltration Evaporation     Prior weather conditions Season Duration of rainfall event Temperature (snowfall) Loss Methods  Horton  With cumulative maximum infiltration  Green-Ampt  Uniform loss  Proportional loss  Initial and continuing loss  Initial and proportional loss  SCS Model  Fraction initial abstraction  Fixed depth initial abstraction Runoff  To obtain the runoff from rainfall excess  Process is called runoff routing Key Parameters  Area  Rainfall  Catchment Slope  Catchment Roughness  Catchment Width and  Length (at times) Land use characteristics What Do We Want to Produce  Hydrographs  Derive peak flow and volume  Related to rainfall frequency  Historic rainfall or design storms Hydrology methods  Rational Method  Laurenson  SCS  Unit Hydrographs – Time Area Rainfall and Runoff Results Many Hydrology Methods      SWMM Runoff Kinematic Wave Laurenson SCS Unit Hydrographs     SBUH, Snyder Rational Time Area Nash, Clark      LA County Method (MODRAT) CUHP Alameda County (Snyder) 2 Sacramento Methods 5 UK Methods  Rational Formula  Plus Regional Methods Rational Formula  Derived from the concept of critical catchment response Qpeak=k*CIA k=unit conversion constant C=runoff co-efficient I=intensity against the ToC A=catchment area Laurenson (rafts) Hydrology  Most widely used in Australia  By Dr. Eric Laurenson Laurenson Hydrology (Contd..)  Non-Linear Reservoir Equation: s = B q n +1 B = 0.285 A0.52 (1 + U ) −1.97 S c − 0.50 * BX * PERN s → storage q → disch arg e n → storage non − linearity exp onent B → storage delay coefficient A → subcatchment area U → urbanized fraction of catchment S c → catchment slope BX → multiplication factor for gauged catchments PERN → function of Manning ' s roughness Time-Area Hydrology  Derived by the British TRRL (1922)  Rainfall excess hyetographs convoluted through the Time-Area diagram Effect of development  Typically impervious and roughness characteristics are modified Direct Rainfall • Land surface grid (DTM) needed • Rainfall applied to grid cells • Initial & continuing or Green • Ampt losses can be applied Surface roughness based on landuse Direct Rainfall (cont.) Questions? Comments? Thank you for joining this presentation, Hydrology 101 By Gavin Fields [email protected] Contact XP Solutions Americas: Asia Pacific: EMEA: +1 888 554 5022 +61 7 3310 2302 +44 0 1635 582555 [email protected] [email protected] [email protected] www.xpsolutions.com