The Internal Green Ampt Parameters, Soil Moisture and IMD for a 100 Year SWMM 5 Simulation for Green Ampt Infiltration

Introduction:  This set of blogs uses the 1000 year rainfall/runoff/hydraulics model that you can download at http://swmm2000.com/forum/topics/1000-year-simulation-with-rainfall-in-swmm-5 to show the inner workings of SWMM 5 and by extension InfoSWMM and H2oMap SWMM using a QA/QC version of SWMM 5 with extended graphics.   I always hope that seeing the inner workings of a SWMM 5 feature helps to understand the code, sensitivity and importance of a parameter.   It also helps show sometimes when a parameter is not important.   In this example, we show some of the internal working of the Green Ampt Infiltration Parameters over the 100 year period. 

Discussion:  Key internal parameters for Green Ampt infiltration are

FUMax is the Saturated Moisture Content of the Upper Zone (internal units of feet)
F or FTOT in the graph is the Cumulative event infiltration at start of time interval (internal units of feet)
FU is the current moisture content of upper zone (internal units of feet)

As shown in Figure 1,  IMD and Soil Moisture are related.  When the soil moisture is zero then the IMD is equal to the maximum values of IMD or IMDMax.

These three parameters are used to calculate the IMD during the simulation among other important uses

IMD =  [ Maximum Allowable Infiltration – Current Moisture Content of the Upper Zone ] / Depth of the Upper Soil Layer

Or  IMD = [ FUMax – FU ] / Depth of the Upper Soil Layer

Soil Moisture = IMDMax - IMD 

Figure 1.   The Internal Green Ampt Parameters, Soil Moisture and IMD for a 100 Year SWMM 5 Simulation for Green Ampt Infiltration



Comments

Post a Comment

Popular posts from this blog

Orifice and Weir flow calculations

Note: Orifice and Weir Flow Computations The orifice flow calculation proceeds as follows: 1. Initially and whenever the setting (i.e., the fraction opened) changes, flow coefficients for both orifice and weir behavior are computed as follows: a. For side orifices: Define Hcrit = h/2 where h is the opening height. b. For bottom orifices: i. For a circular orifice, compute area over length (i.e., circumference) as AL = h /4. ii. For a rectangular orifice compute AL = h*w/(2*(h+w)) where w is the opening width. iii. Compute Hcrit = Cd*AL/0.414 where Cd is the orifice discharge coefficient. At step 1b, the critical head for the bottom orifice, where orifice flow turns into weir flow, is found by equating the result of the orifice equation to that of the weir equation Cd*Area*sqrt(2g)*sqrt(Hcrit) = Cw*Length*sqrt(Hcrit)*Hcrit or Hcrit = (Cd * Area) / (Cw/sqrt(2g) * Length) The value of Cw/sqrt(2g) for a sharp crested weir is 0.414.
Read more

SWMM 5 Error Messages

Engine Error Number Description ERROR 101: memory allocation error.                                                                                             ERROR 103: cannot solve KW equations for Link                                                                                   ERROR 105: cannot open ODE solver.                                                                                              ERROR 107: cannot compute a valid time step.                                                                                     ERROR 108: ambiguous outlet ID name for Subcatchment                                                                            ERROR 109: invalid parameter values for Aquifer                                                                                  ERROR 110: ground elevation is below water table for Subcatchment                                                         
Read more

EMC Washoff in SWMM5

Image
There are four steps to using EMC concentrations in your network: 1. Define your pollutant by adding a pollutant using the Data=>Quality=>Pollutant command : 2. Define the Land Use by using the Data=>Land Uses command or the Land Use Editor: 3. Define Buildup to be None by clicking on the None Tab: 4. Define the EMC Washoff concentration by clicking on the Washoff Tab: This is where you would add a GW concentration More: http://www.swmm2000.com/
Read more