Geology Report
Corentin Liber
March 29, 2013
We made some advancements in the stream bed project so we think it's time to send a global report on our activities on this one.
The object of this survey was to study the erosion traces left by a (now dry) modern stream bed and deduce a maximum of information from it such as its maximal flow, regime, etc.
The first step was to locate such a stream bed. We checked by aerial imagery some areas with promising features before coming to the MDRS using Google Earth and checked some of the when we arrived.
We found one suitable bed the first day and began to study it quite soon.
We went on EVA each morning to collect data and worked on it during the afternoons ans evenings.
The first data we collected were the wetted perimeter, depth, width and inclination of the slope. We decided to work on a 670 meters long segment of the main stream bed and took measurements at 13 different points along the bed, most of the time where a secondary bed was linked to the main one. We used the Manning Formula to compute the flow and average speed from our data and worked on several shape models of the bed: rectangular, circular and one based on Fermi. The results show an increase of the flow as we go down the stream which is coherent with the reality.
The next step was to incorporate the incoming flows into the main one to check if the differences add up correctly. We took measurements just before the junction between the secondary and main beds for 24 secondary stream beds. We collected data in several points within 10 meters in the secondary beds and will take the average flow in consideration for the model.
We expect to find a great difference as the additional incoming flow should be quite superior the the increase in the main flow considering the infiltration that should be consequent. After we study the data this evening, we should have an estimation of the infiltration and we'll test it on the field in a future EVA.
To improve the precision of the model, we'll be going back to the main stream bed to take photos at short regulars intervals (around 10 meters) to be able to divide the bed in smaller sections and to apply to each one the best shape model based on what we record on site. We plan to take additional measurements in the main bed as we find 13 is not sufficient for a good estimation.
At last, we will be able to use a statistical approach of the model if we reach a sufficient amount of data collection points.
All the coordinates of the measurements points were recorded using the GPS, a map of the area and photos taken from high places around the survey area. By combining these different informations, we could map the whole survey area and the resulting map is quite precise. We could extend it easily if we decide to widen the studied zone.
As the area sometimes present problems with the communication (impossibility to contact the Hab) because of the surrounding relief, we are planning to test the quality of the signal at regular distance intervals and report it using this map, eventually on a wider scale if we have enough time. This could provide useful information for the next crews and prevent contact difficulties with the Hab in case of an emergency in the area.
The model is using the program Matlab and the mapping of the area is done using ArcGIS.