Installation | Usage | Parameters |
- Q: Can ArcNLET be installed with ArcGIS10?
A: Yes (as of version 1.1).
- Q: How to upgrade ArcNLET to a newer version?
A: On Windows 7, the software can be uninstalled from the control panel as
described in Section 3.1.2 of the User's Manual. On Windows XP, it may be necessary to run the setup.exe file of the currentlyy installed version
as administrator and select "Remove ArcNLET".
- Q: Can LiDAR DEM be used in the software?
A: Yes. Please refer to Section 2.1 of the Application Manual.
What are the units of the nitrate plumes (i.e., the output of the Transport module)? What are the units of the output nitrate load
(i.e., the output of the Nitrate Load Estimation module)?
A: The plumes have units of concentration (mass per
volume, M/L3)and are the same as the concentration units of the source plane (C0).
The units of the output load are mass per time (M/T) with the
mass portion of the units the same as the mass units of C0 and the time
portion of the units the same as the time units of hydraulic
conductivity (L/T) and the decay coefficient (1/T). Refer to
Table 5-1 of the User's Manual for a complete listing of parameter
- Q: How do I decide the level of post-processing to use?
A: If one is only interested in the load calculation and not in the plume distribution
then one can use the 'None' option for a shorter run time. If one is interested in the plume distribution and the area of interest
has small water bodies (e.g., ditches) one should use 'Full' option. Otherwise, medium (the default) is sufficient.
- Q: Why are some plumes sometimes not displayed?
A: There are three main reasons for this (1) septic tanks that lie within a water body are excluded from calcuation. This can be corrected
by adjusting septic tank locations as needed.
(2) If a plume is too short (due to a large decay rate, small flow velocity, low longitudinal dispersivity or any combination thereof),
it will not be displayed.
(3) Another reason why a plume may not be displayed is related to the warping algorithms used. This situation rarely occurs and does not affect the nitrate load calculation
- Q: How to choose the values resolution and step size in the Particle Tracking module?
A: These values are automatically calculated by the software. Making these values smaller
is better however this will result in increased execution time and memory usage.
- Q: What value should be used for the smoothing factor?
A: The smoothing factor is determined based on calibration by comparing the smoothed DEM with observed hydraulic head.
An example of determining this factor is given in Section 4.3 of the Application Manual.
- Q: What value should be used for the source plane height, Z?
A: This coefficient is in general determined based on field observations of vertical nitrate profile near the sources. If the profile is
not available, one may choose another option of "Specified_Input_Mass_Rate" that determine the Z value based on the equation of Section 4.2.1 of the Technical Manual.
- Q:Is ammonia considered when estimating the nitrate concentration?
A: No. This software only considers nitrate transport. The source plane contraction C0 is for nitrate only.
- Q: What are the ArcNLET default parameter values? Are they recommended to be used for any simulations?
A: The default values are for training purposes only; with these values, first-time users of ArcNLET can run the model without worrying about what values to use. The values are from literature and should be adjusted for different sites of interest. The application manual describes how to obtain hydraulic conductivity and porosity from SURRGO database and how to calibrate model parameters based on observations of hydraulic head and nitrate concentration. If these data are not available, the users need consult a hydrogeologist for reasonable values of the model parameters.
- Q: Clicking the Help menu entry in the software brings up an error message saying that the system can't find the specified file.
A: The help file (users_manual.pdf) must be downloaded separately and placed in the installation folder.
- Q: The transport module appears to run slowly under ArcGIS 9.x
A: The Spatial Analyst libraries of ArcGIS 9 have been improved in ArcGIS 10 which results in faster model excecution and lower memory usage.