#Ask - Data Collection Steps
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aliyya tirangga
May 30, 2024, 12:19:05 PMMay 30
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Hi, I have several questions that makes me getting curious about those. I think these are basic questions but I have to confirm something. Here are my questions:
1. If we want to conduct regional scale groundwater modeling (watershed scale), what is the average spatial resolution required for elevation data? Is SRTM data with a 30 m spatial resolution representative enough to be used as digital elevation data in our model?
2. Related to question no. 1, I had an issue when I tried to delineate a catchment and generate streams based on a GIS approach using SRTM data. The location of higher-order streams, which I assumed to be rivers in my model, did not spatially align with the real rivers that I had delineated using Google Satellite aerial photos. Some segments of the real rivers were not located in valley topography on the SRTM data. How should I deal with this issue? Which river data should be used?
3. Are elevation data (river stage, lake stage, water table elevation from dugwell) sourced from handheld GPS measurements representative enough to be used for regional scale modelling? Regarding the third question, is the accuracy level of handheld GPS tolerable in the model? If not, is there any other more practical and low-cost method/tool?
4. Is there a practical and low-cost measurement method or instrument to measure riverbed sediment thickness and its hydraulic conductivity? How can this method be applied to large and deep rivers?
Thank you.
2. Related to question no. 1, I had an issue when I tried to delineate a catchment and generate streams based on a GIS approach using SRTM data. The location of higher-order streams, which I assumed to be rivers in my model, did not spatially align with the real rivers that I had delineated using Google Satellite aerial photos. Some segments of the real rivers were not located in valley topography on the SRTM data. How should I deal with this issue? Which river data should be used?
3. Are elevation data (river stage, lake stage, water table elevation from dugwell) sourced from handheld GPS measurements representative enough to be used for regional scale modelling? Regarding the third question, is the accuracy level of handheld GPS tolerable in the model? If not, is there any other more practical and low-cost method/tool?
4. Is there a practical and low-cost measurement method or instrument to measure riverbed sediment thickness and its hydraulic conductivity? How can this method be applied to large and deep rivers?
Thank you.
Jakab Andras - Gmail
May 31, 2024, 5:53:27 AMMay 31
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The 30 m resolution SRTM should be fine as the regional scale model would presumably have a rougher grid resolution than that. Nevertheless, the SRTM maps that are downloadable are not necessarily reflecting the true ground surface elevation especially if the land cover is complicated. I'm, however, not sure about this, so I would also love it if someone could share some more info on the SRTM accuracy.
As far as the catchment delineation is concerned, although I'm not an expert on this topic at all, I believe it needs calibration against true locations of the surface water features (e.g., by using Google Earth information, etc.). If you can't perform that kind of calibration then it's better to use a photo for your stream locations instead of a GIS generated catchment delineation outcome. Catchment delineation is rather sensitive to the topography and the less topographic variability you have (i.e., low-lands, etc.) the less accurate your delineation will be.
There is no single answer here. Everything depends on the modeling goals of course. What you may also do here, is to include measurement error in your observations, calibrate the model accordingly, and present your results with uncertainties being quantified. See manuals and presentations about automated calibration tools such as the PEST family of programs.
Riverbed sediment thickness is something that may even not exist. Not all surface waters have sediments on top of their beds. In MODFLOW the riverbed thickness and the vertical hydraulic conductivity of the sediments, therefore, in such cases, may be considered as surrogates for something that doesn't have a physical equivalent. As a result, these parameters are most often calibration parameters, and not being measured.
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Saul Montoya
Jun 1, 2024, 11:21:36 PMJun 1
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You can delineate a catchment using a SRTM or Aster Dem online without any preprocessing with Hatari Utils.
Please look at this tutorial:
Hatari Utils link.
Saul Montoya M.Sc. Dir: Caminos del Inca 288 dpto 302, Surco, Lima 33 | Tel.: (511) 4491922 | Cel: Nuevo! (51) 984 115 861 | Web: gidahatari.com |
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