Options - Drainage

The drainage category includes the following properties related to Drainage Networks. Note that these parameters will be the values adopted when creating a catchment. You will be able to edit the values in the Catchment later:

• Runoff Coefficient (C, Double) - Also called infiltration coefficient, run-off, or simply C
  This coefficient can be given by this table:
  
  

  Location	C
  Roofs and asphalted surfaces	0.00 to 0.95
  Cobblestones, tiles, blocks with well-taken joints	0.85 to 0.90
  Irregular stone pavements	0.50 to 0.70
  Gravel roads and walks	0.15 to 0.30
  Parks, gardens, lawns	0.01 to 0.20

  
  This table can be further simplified by:
  C = ((Covered area) * 0.7 + (Uncovered area) * 0.3) / ((Covered area) + (Uncovered area))
  Understand the covered area as a very impermeable urbanized stretch and uncovered as rural areas.
  As a matter of fact, many prefectures impose values of C. Curitiba, for example, determines that you use C = 0.95 to 1.00 in central areas and 0.8 in other regions.
  
• Calculation Method (Mcr, Enumerator) - Apply or not the Fantoli coefficient to the flow calculation in the equation:
  Qesc = Qmon + F * SCXA * Cr * I
  • Default - This coefficient is not applied
    F = 1
  • DNIT - The coefficient will be calculated by the equation:
    F = 0.0725 * (I * TM) ^ (1 / 3))
  
  Where:
  • Qmon - sum of point flows entering the structures upstream of the pipe
  • F - Fantoli coefficient
  • SCXA - Sum of the runoff coefficient (C) multiplied by the contribution area in the pipe upstream structures
  • Cr - Coefficient of delay
  • TM - System time (greater value between concentration times and upstream travel times added)
  • I - precipitation, as a function of the rainfall equation, system time (TM) and return time (Tr)
• Distribution Coefficient (n, Double) - Coefficient applied to the calculation of flow in large catchments
  The distribution coefficient (n) corrects the effects of the distribution of rainfall considered uniform in the Rational method, mainly in medium-sized catchments, with areas greater than 1 km². This coefficient is given as a function of the Catchment area and a coefficient related to the average slope or the area itself.
  In the Rational Method, the throughput is given by Q = C * I * A
  In the Modified Rational Method, it is given by: Q = CR * C * I * A
  
  CR = A^(-n)
  Being:
  Q: flow
  I: precipitation
  A: Catchment area
  n:distribution coefficient
  
  The DNIT hydrology manual (IPR 715 / 2005, page 128) uses n= 0.15 for urban works and 0.10 for rural works
  The program allows you to define values for the distribution coefficient in intervals of the area, by clicking the button: that appears when selecting this property:
  
  
• Rain equation - The rainfall equation to be used in the calculation of all Drainage Networks in the current project must be based on the time of concentration (tc) and the time of recurrence (Tr)
  These equations usually have this format: I = A * Tr ^ B / (tc + C) ^ D
  Where A, B, C and D are tabulated coefficients.
  You can obtain these parameters from the Plúvio provided by GBRP - Water Resources Research Group.
  You can also get the equation by clicking the button . See more in the topic Rainfall Equations
• Precipitation (I, Double) - This property appears here so you can test the equation chosen above. If you see any odd values here, your equation has a problem. Compare the example:
  
  
• Tc Equation (TcEq, TcEquation) - Informs which equation will be used to calculate the concentration time (tc)
• Time of concentration (Tc, Double) - the time of concentration of a hydrographic Catchment is defined by the travel time that the runoff takes to reach the main course from the most distant points to the place where you want to define the discharge.
  
• Minimum Concentration Time (TcMin, Double) - When the calculated or arbitrated concentration time of the basins associated with the device is lower than this value, this value will be adopted
• Time of recurrence (Tr, Double) - It is the time of recurrence of the rain, or time it takes to repeat a rain of equal intensity and duration. According to CETESB, it ranges from 2 to 10 years:

  Location	years
  Residential	2
  Commercial	5
  Areas with public buildings, airports	2 to 5
  Highly valued areas	5 to 10

  
  The IS - 203 - Hydrological Studies (das Basic Guidelines for Preparing Road Studies and Projects) recommends Designing using 10 years and checking the amount levels in 20 or 25 years old