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| {{learned|what the rainfall overlay is|how the rainfall overlay can be used|how the rainfall overlay can be configured|what principles govern its calculation}}
| | [[File:Rainfall-Overlay.jpg|thumb|right|200px|Rainfall overlay]] |
| | The Rainfall Overlay is a variant of the [[Water Overlay]], which in turn is a [[Grid overlay|grid overlay]]. Water overlays are connected to the [[Water Module]], a complex hydrological calculation module within the {{software}}. |
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| Calculations and numerical principles can be found on the [[Rainfall overlay calculations]] page.
| | The Rainfall overlay specializes in displaying the hazard and impact of (heavy) rainfall over the project area. Based on the elevation model, terrain roughness and representations of the sewer and water systems, several result types can be generated by the accompanying Water Module. |
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| Please click on [[Rainfall_Overlay_tutorial|tutorial]], to get started on using the overlay.
| | A [[Rainfall_Overlay_tutorial|Rainfall Overlay Tutorial]] is available to get you started with this overlay. |
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| ==Result types==
| | In order to get more familiar with the different components of the Rainfall Overlay check out Quadrant 2 of the [[Testbed_water_module|Water Module Testbed]]. This Testbed is available to you as a project in the {{software}}. |
| The rainfall overlay is a [[grid overlay]] showing results of heavy rainfall on the surface (inundation), sub-surface (groundwater), open water and sewer system. The following results are produced:
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| * '''BASE_GROUNDWATER_DISTANCE''': shows the distance between the surface level and the initial groundwater level in centimeters (NL: ontwateringsdiepte). For now, the height of the ground level is including the buildings and other objects on the ground (the height to the surface). This will be changed to the terrain height in a following release.
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| *'''BASE_TYPES''': shows the division of the grid cells in water, land or sewer areas that are connected to the sewer. Playing with the grid cell size, will make this division between areas/terrain types more or less accurate, which affects the calculation of the flooding.
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| *'''EVAPORATED''': shows how much water is evaporated after the rainfall in the defined simulation time. For more information on how this layer is calculated, see the [[Rainfall overlay calculations]] page.
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| *'''IMPACTED_BUILDINGS''': shows all constructions or neighboring cells which will be flooded with the settings as provided in the rain overlay wizard and the IMPACT_FLOOD_THRESHOLD_M attribute (see attributes of the rainfall overlay). The result type shows therefore which constructions or neighboring cells are more flooded than the defined threshold. The colors are based on the attribute 'Critical infrastructure' in the function values table, in where a classification is made in the importance of flooding of different types of buildings. Three values are by default entered in the function values table: 0 (not very critical, for example a shed or a park), 1 (important, most buildings), 2 (critical, such as a hospital or a school).
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| *'''SEWER_LAST_VALUE''': The amount of water remaining in the sewer after the simulation is over
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| *'''SEWER_MAX_VALUE''': The largest amount of water that was in the sewer at any time during the simulation
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| *'''SURFACE_DURATION''': The total amount of time the surface has a certain amount of rainfall on it. The amount of rainfall is adjustable with the water on surface threshold (m) in the rainfall overlay wizard. The default value of this threshold is 0.
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| *'''SURFACE_FLOW''': The total amount of water which has flowed across the surface
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| *'''SURFACE_LAST_VALUE''': The amount of water remaining on the surface after the simulation is over
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| *'''SURFACE_MAX_VALUE''': The largest amount of water that was on the surface at any time during the simulation. Differs from WATER_STRESS in that water stored on bodies of water is always included.
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| *'''UNDERGROUND_FLOW''': The total amount of water which has flowed underground
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| *'''UNDERGROUND_LAST_VALUE''': the amount of water which has flowed underground after the rain simulation is over.
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| *'''UNDERGROUND_MAX_VALUE''': the largest amount of water that flowed underground at any time during the simulation
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| *'''WATER_STRESS''': The maximum amount of excess water at any time during the simulation. Differs from SURFACE_MAX_VALUE because water stored on bodies of water are not immediately deemed "excess", this depends on the threshold value (ALLOWED_WATER_INCREASE_M) which can be defined in the last step of the [[#Rain overlay wizard|rain overlay wizard]] or in the ''Keys'' section of the overlay. If the amount of water exceeds this threshold value, the amount of water is visible on the water bodies.
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| ==Hydrological and hydraulic concepts== | | ==Rainfall overlay results== |
| | The Rainfall Overlay is a Water Overlay that is connected to the Water Module. This Water Module performs two dimensional grid based water simulations for a large set of input data and parameters, configured mostly through a related [[Water Overlay Wizard]]. When a simulation finishes, the module stores the result in the Rainfall overlay based on the selected result type. Only one result type can be stored per Rainfall overlay. |
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| ===Concepts===
| | The Water Module however, is not restricted to generating only one type of result. Instead it can produce multiple unique result types for one single simulation. |
| For the computation of the Rainfall Overlay several concepts are incorporated, which will be briefly described in this section. All For more details, please read the reference page:
| | Fortunately it is possible to add additional result type overlays which relate to a particular Rainfall overlay. These are known as [[Result Child Overlay]]s. Again, each child overlay only stores one particular result type. |
| * Rainfall 2 runoff concepts, describing the transport of rainfall via roofs, paved and unpaved areas to the groundwater, sewer system and/or surface in every cell
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| * An inundation concept, describing the process of overland flow (also referred to as sheet flow), when runoff exceeds the transport capacity of the sewer system.
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| * A groundwater concept, describing the transport of water trough the sub-soil.
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| * A sewer concept, describing the transport of water trough the sewer system.
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| * A surface water concept, describing the transport of water trough a polder system
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| The rainfall 2 runoff model, inundation model and groundwater model use a computational cell as unit. The sewer and surface water models use larger areas, referred to as districts, as primary unit.
| | Apart from multiple result types, the Rainfall overlay can also store result data of multiple, intermediate simulation results, instead of just a single end result. These intermediate simulation results are known as [[timeframes (Water Overlay)|timeframes]]. |
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| The rainfall overlay can be linked to the subsidence overlay to see the impact of subsidence on inundation. See therefore the section about [[#Including_subsidence|including the subsidence overlay]].
| | For the full list of result types, see [[Result type (Water Overlay)#List of Result Types|List of Result Types]]. |
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| [[File:Rainfall Overlay scematic.png|600px]] | | For other results, which are not overlay results, but still related to the simulation for a particular Rainfall overlay, see [[Results (Water Overlay)|Rainfall overlay results]]. |
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| Rainfall and evaporation are supplied as input data. Depending on the topography assigned to a cell ''rainfall'' contributes to storage (e.g. trees, roofs, etc) on paved (houses, roads, etc), unpaved (e.g. green zones) or open water areas from which ''evaporation'' can take place, depending on the topography of a cell. In case these storages are depleted: | | ==Module== |
| * In case of unpaved topography excess water contributes directly to surface ''(SCF)''
| | A Rainfall Overlay can be configured by opening the Rainfall Overlay Wizard. More in-depth information can be found under each of the categories below. |
| * Excess water from paved cells contributes to sewer storage ''(SIF)'' of the sewer district. If insufficient storage is available in the sewer district, water contributes to surface storage ''(SCF)''
| | {{Water Module buttons}} |
| From the surface storage water can directly infiltrate ''(INF)'' to the sub-surface if both the infiltration capacity and sub-surface storage is sufficient.
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| Water can flow from cell to cell via the surface ''(RUN)'', using all terms in of the dynamic wave equations relevant to describe rainfall induced flooding. If surface runoff contributes to a cell with an open water topography it contributes to the storage of the water district. Cell to cell ground water flow ''(GWF)'' is represented by Darcy's law. | | ==References== |
| | # [[Water Module Theory#Formulas|Water model formulas]] |
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| The sewer system and surface water system are represented by districts. Water from sewer districts ''(SEW OUT)'' is assumed to be pumped to a treatment plant and extracted from the model domain. The surface water system can consist of multiple water districts (for now we use peilgebieden), which have a typical drainage level. Outflow from each district ''(DIST OUT)'' can be extracted from the model domain or contribute to another district via hydraulic structures. Currently weirs, culverts and pumps are incorporated in the model.
| | {{WaterOverlay output nav}} |
| | | {{Overlay nav}} |
| ===Scope of application===
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| The rainfall overlay is typically used to show impact of heavy rainfall, typically more than 20 mm/hour in urban areas, in flat till mildly-sloped areas. It includes all processes describing what is commonly referred to as pluvial flooding or flash floods.
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| Please bear in mind the following:
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| * As the sewer system is simplified to districts, flooding due to sewer surcharge (water ex-filtrating from sewer systems) due to insufficient sewer capacity is excluded
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| * As the surface water system is simplified to districts, flooding due to over-topping canal embankments is excluded
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| * The total simulation time is by default divided by 2000 time steps (referred to as cycles). When the total simulation time is increased, the amount of cycles can be increased when necessary to assure accurate simulation results results.
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| ==Rainfall overlay wizard==
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| The rainfall overlay can be added to the project multiple times, to present different outcomes or scenarios and compare these, for example for different rainfall amounts. For information on adding and removing the overlay to and from the project, see the page about[[overlay#Adding and removing overlays| overlay]]s in general.
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| When no input data is provided, results will be computed using default values and assumptions. To specify input, the rainfall overlay wizard is developed.
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| ===Step 1: Defining the weather===
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| In the first step the weather can be defined. Currently rainfall and evaporation are assumed uniform over the project domain; no variation in space can be specified.
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| [[File:Step1-weather.PNG|400px]]
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| At this screen you can define:
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| # a rainfall event and give it a name
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| # the length of the rainfall event and the dry period after the event. The sum of these determine the period over wich a simulation is run
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| # the total rainfall amount in mm which will be distributed over the length of the rainfall event
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| # the [[Rainfall_overlay_calculations#Evaporation_&_the_vertical_water_balance| reference evaporation]] rate in mm/day
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| # a rainfall-pattern, currently defined in 1-10 sines, which can be controlled by the slider
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| ===Step 2: Setup of the water system===
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| The overlay model can be defined by providing the following data:
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| *water areas (for now typically peilgebieden)
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| *sewer districts (rioleringsgebieden)
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| *hydraulic structures (culverts,weirs and pumps)
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| *initial groundwater levels
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| ====Water areas====
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| Water areas are imported as one or multiple [[area]]s and have one uniform representative water level. Water from one water area can flow to an adjacent water areas via [[#Hydraulic structures|hydraulic structures]]. Water can be extracted from the water system by specification of an outlet.
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| [[File:Step2-water_areas.PNG|400px]]
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| Water areas are defined by uploading a [[geojson]] file. The following attributes are needed for the calculations.
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| {| class="wikitable" | |
| ! Attribute
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| ! Description
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| ! Example
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| ! Remark
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| | NAME
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| | The name of the water level area.
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| | PG 256
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| | This attribute is not loaded in as attribute, but can be used as name to identify the resulting area in the Engine later on.
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| |-
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| | WATER_LEVEL
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| | The height of the water, in meters relative to reference (mNAP in The Netherlands).
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| | -1.5
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| | This is mandatory information
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| | OUTLET
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| | The amount of water which disappears from this level area in cubic meters per second (m3/s).
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| | 1.65
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| | This could also be the outlet of a ''gemaal''
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| |}
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| ====Initial groundwater level====
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| This step in the rain overlay wizard provides the possibility to upload a GeoTiff file with groundwater levels in m relative to reference level (NAP in The Netherlands). By default the groundwater level of the water level areas is used (for example the Gemiddelde Hoge Grondwaterstand in Dutch cases). The soil layer between the surface and the groundwater is available for storage.
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| ====Sewer areas====
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| The next step allows for the sewer areas to be uploaded. The file is loaded in as a [[geojson]] file as [[area]]s. The following attributes are needed:
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| {| class="wikitable" | |
| ! Attribute
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| ! Description
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| ! Example
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| ! Remark
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| | NAME
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| | The name of the sewer.
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| | Sewer North-East
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| | This attribute is not loaded in as attribute, but can be used as name to identify the resulting area in the Engine later on.
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| |-
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| | SEWER_PUMP_SPEED
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| | The speed at which water is pumped out of the sewer, in cubic meters per second (m3/s).
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| | 0.0012
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| |-
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| | SEWER_STORAGE
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| | The amount of water which can be stored in this sewer, in meters (m).
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| | 0.007
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| | The total amount of storage for this sewer is the surface area of the [[construction]]s which are connected to the sewer in this particular sewer area, times this attribute.
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| |}
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| If no sewers exist, the model has no water flowing into sewer containers for storage. Therefore, you can automatically generate these areas. For more information on how the generation of these areas is done or about the sewer system in general, see the [[Rainfall overlay calculations#Sewer system|Rainfall overlay calculations]] page.
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| ====Hydraulic structures====
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| [[#Water areas|Water areas]] can discharge to adjacent water areas and [[#Sewer areas|sewer areas]] can discharge to water areas by means of the hydraulic structures. Hydraulic structures are loaded in the project using the rainfall overlay wizard. The following structures are implemented:
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| * Weirs, culverts and pumps, connecting [[#Water areas|water areas]]
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| * Sewer overflows, connecting [[#Sewer areas|sewer areas]] to [[#Water areas|water areas]]
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| The following attributes need to be present.
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| {| class="wikitable"
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| ! Attribute
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| ! Description
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| ! Example
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| ! Remark
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| | NAME
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| | The name of the weir.
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| | PG 256
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| | This attribute is not loaded in as attribute, but can be used as name to identify the resulting contruction in the Engine later on.
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| |-
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| | WEIR_HEIGHT_M
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| | The height of the weir (crest level), in meters relative to the reference level used (NAP in The Netherlands).
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| | -1.5
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| | WEIR_WIDTH
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| | The width of the weir (crest) in meters.
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| | 1.2
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| |-
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| | WEIR_COEFFICIENT
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| | The loss coefficient of the weir (a combination of contraction and other losses).
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| | 0.6
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| | WEIR_N
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| |-}
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| Weirs must overlap with at most 2 water level areas. If a weir overlaps with more that 2 water level areas, 2 areas are selected at random which the weir pumps between. If a weir overlaps with only 1 water level area, only its outlet function is processed. Structures which do not overlap with any water level areas are imported for visualization, but do not transport any water.
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| ===Step 3: Hydrological coefficients===
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| In the next steps of the wizard, hydrological coefficients regarding the surface and the underground terrains, can be edited.
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| For each of these coefficients, representative values are already entered in the forms.
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| *Water infiltration (m per day): the speed by which the water infiltrates the underground. The speed is also determined by the underground water infiltration factor. From these two values, the lowest value is used.
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| *Water manning: the Gauckler Manning coefficient, often denoted as n, is an empirically derived coefficient, which is dependent on many factors, including surface roughness and sinuosity. For more information about this formula see [[Rainfall_overlay_calculations#Manning_formula(surface_runoff)|the Rainfall overlay calculations page]].
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| *Water evaporation factor: this factor will be multiplied with the general reference evaporation.
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| *Reference Evaporation (mm per day): The Makking reference evaporation factor. This value ranges from 0.5 mm per day in the winter till 3 mm per day in the summer for the weather station ‘ De Bilt’ in the Netherlands.
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| *Water storage fraction: the percentage of underground volume that can be used for the storage of water. This number is determined by the difference between the ground water level and the surface height times the surface area.
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| *Vertical to horizontal infiltration factor: This factor will be multiplied with the vertical infiltration speed, to obtain the horizontal infiltration speed.
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| [[File:Visualisatie_wateroverlast.JPG|400px|thumb|right|Schematic visualization of the water flow over the water level areas and hydrological constructions.]]
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| ==Building functions==
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| Since [[construction]]s in the Engine have an effect on the flow of the water, for example if a building has a green roof, attributes concerning these values can be adjusted in this step of the wizard. Representative values are already entered in the table. The same values can also be adjusted in the [[Functions#Editing functions|function values window]].
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| ==Visualization of the water system==
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| In the last step you can choose for a [[#Result_types|result type]], as listed above. If you have provided the water level areas and the hydrological constructions to the Engine, along with the required attributes, a schematic visualization of the water flow from the various water level areas and the hydrological constructions is visible. The red spheres stand for water flowing from a weir to another water level area. The green spheres stand for a weir receiving water from a water level area. The speed of the spheres is based on the WEIR_SPEED and the OUTLET values. If no spheres are visible, the water flows very gently between these water level areas. The pop-ups in the 3D world are panels which mark the middle of the water level area or the place of the hydrological constructions. In these panels, the provided attributes, such as the WATER_LEVEL_M or the WEIR_HEIGHT can also be edited. Play around with this to see how the water flow changes.
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| ==Including subsidence==
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| [[File:Subsidence_attribute.JPG|400px|thumb|right|Create a new attribute containing the recalculated water levels.]]
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| [[File:Include_subsidence.JPG|400px|thumb|right|Include the subsidence overlay and select the new water level attribute.]]
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| For the calculation of the effects of a severe rainfall, effects of subsidence can be included, such as the recalculated water levels and the changed ground levels. For now, ground water levels affected by the subsidence are not included.
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| {{Editor steps|title=include subsidence|Add the [[Subsidence_(Overlay)|subsidence overlay]]. Take note of when to use and how to configure the subsidence overlay.|In the [[right panel]], select the "Keys" tab|Select the "Area attribute: output level (m)". Choose a new attribute, for example the WATER_LEVEL_OUTPUT attribute, to write the new water levels to. |In the Rainfall overlay in the [[right panel]], select the "Keys" tab.|Choose the overlay for the subsidence model you want to use in the "Include Subsidence" form.|Also select the newly created attribute containing the water levels in the "Area Attribute: Water Level (m)" form.|Go to the "General" tab and recalculate the grid.}} | |
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| Be careful not to write the new water levels calculated in the [[Subsidence_(Overlay)|subsidence overlay]] to the already existing water level attribute, otherwise the subsidence model will be recalculated with incorrect values when refreshing this overlay.
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| You can play around with the results of the two overlays and compare, for example, two rainfall overlays where one overlay takes the effects of a subsidence model into account and the other overlay shows results without these effects.
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