The entire area that contributes water to the reservoir ( the contributory area )

is an important consideration.

Rainfall, snowfall, rock types soil types, vegetation, runoff gradients,

construction activities, road cuts and fills, land use, forest fires.

Surely topographic maps already exist of the watershed.

Google Maps and Google Earth will reduce your work load.

Remember to work smart not work hard.

Small reservoirs have a limited lifespan.

Large reservoirs have a long lifespan.

The life of a reservoir begins with the construction of a Dam.

There will be records if you look for them hard enough and long enough.

Weather services keep records of rainfall events for years.

Reservoirs have initial volumes, and contributory areas have measured

surface areas that provided materials to completely fill that volume

in a specific time frame.

Many reservoirs operate for years, and then one great rainfall event

fills them up completely with eroded soil in a few hours.

Historical areal photographs will help determine the initial conditions

prior to the dam construction. Militarys and Governments love to keep

old and new recon photos.

A series of photos could help you determine conditions at several

time periods.

Thanks for your feedback. It's appreciated. I will definitely be looking in to a few of those aspects now.

A geological map is a symbolic depiction of reality and as such final results are deeply conditioned by your initial aims. So you should be clear about the aims of your mapping before starting to collect data. In any case, some considerations and recommendations are always working.

Before you start with the acquisition of new data you should do three things: i) retrieve all the information already available in the study area, ii) retrieve the available historical maps (e.g., vintage topographic and geological maps) and aerial photographs, iii) make a preliminary geological and geomorphological survey with an appropriate scale, highlighting all the elements useful to the realization of your map. In this way you can have an initial idea of the geological and geomorphological setting of the site and you can better design new surveys to be carried out.

The GPR can be useful, but you have to get an idea of the thickness of the alluvial deposits, because you know that the depth of study that GPR can achieve depends primarily on the frequency used and, therefore, the type of antenna you will use. In order to design the best GPR survey campaign you should also approximately know the textures of the alluvial sediments and the depth of the water table.

Even the ERT can be very useful in this case, especially if you expect to have a good resistivity contrast, both between the covers and geological substrate and within the alluvial deposits.

Anyway, GPR and ERT still need to be calibrated with direct information of the subsurface. So your idea about sampling the subsoil is very useful. How you will take the samples? Are you performing mechanical or manual sampling? In the event that the grain size of the deposits is very coarse, it will be difficult for you to reach an adequate depth. You should take this into account before you start.

With regard to laboratory analysis, you could perform the grain size analyzes on the core samples. In this case, you have to properly evaluate the quality of your samples, because a loss of fine grain material during sampling may cause an underestimation of such material.

Finally, I suggest you create a GIS in your area of study, so that you can better manage your information, both previously available and newly acquired. With the GIS also the realization of final maps and geological cross-sections would be much easier. There are open source GIS, such as Quantum GIS (http://www.qgis.org/), which allow you to work very well.

For a general overview of the geology of an area you usually need to know the rock types at the area of interest, the orientation of their foliation-bedding (if they have), the type of the geologic contacts and the major structures of the area (faults and folds). Depending on the purpose of your project additional geologic information could be helpful, for example discontinuities, weathering etc. The aim of the project will designate the type and amount of information you need.

Thank you both, Massimiliano and George! I never thought of doing any ERT tests but now that you mention it, it should have been in my mind from step one. GIS will certainly be used, but thanks for recommending Quantum GIS. I had never heard of it before your mentioning. George, my final project is aimed towards quantifying the amount of sediment deposited with the dam in place while investigating where this material came from. I've done work in compiling maps of the contributing area to the reservoir and the geology of the area. With this being the case I should be able to come up with a good idea of what the sediment will look like upon further reviewing the rock units included in the contributing area. Could you think of anything else that would be useful to me with this in mind? All of the help posted has brought up some very useful considerations, I thank you all!

Petrographic analyzes on rock fragments coming from your samples and x-ray could help you to make comparison with rock units. Petrofacies and petrostratigraphy desumed from your samples could help you in reaching your goals, when compared with all the available information (geology, weathering, runoff, etc.)

Some useful information, apart from the ones already mentioned, could be a map with the topographic gradient of the contributing area (it shouldn’t be too hard to make one with a GIS), the vegetation coverage, weathering conditions of the rocks, any natural springs in the area and big or small slides or generally mass movements upstream.

It would be instructive to cut a smooth face and take pictures of the sediment layers

to see if there are any Varves ( alternating winter and summer layers ). If there are

any Varves, the summer layers will be lighter in color and thicker, while the winter

layers will be thinner and darker in color. Lighter layers form when micro-organisms

consume the available nutrients in the summer run off periods and deposit their own

calcium rich deposits mixed with what they could not digest. In the winter they

are not as active or plentiful so the deposited layer is " unconsumed " and thus darker and still full of nutrients.

I have noticed these Varves in 70 million year old ocean floor layers, which are

currently tiled up vertically, and, in layers inside a Cave I visited often when I

was much younger.

Since the deepest erosion will be near the original dam location,

you should be able to scrape a vertical face with shovels and trowels to

get below the plant and weather disturbed soils down to the annual Varves.

In both the 70 million year old layers and the cave sediment layers, the

alternating pair of layers was about 5 mm thick. It will be interesting to

see if the layers in a reservoir are similar, or if they vary wildly in thickness

year to year as rainfall patterns and run off ( sediment load ) vary.

I don't know where your site is but in the UK reservoirs may be periodically drained for inspection exposing the sediments. I have sampled a 4 m high wall of sediment using monolith tins banged into the incised sediments - quickly as the dam was re-filling. Usually we sample from a boat, but seeing a drained site give you a good idea of the variations across the bed of lake that can occur (e.g. delta -like features from side streams). In some areas reservoir sites have been drained down and the wall breached / kept open due to (I assume safety issues) where the wall is old / failing (in some areas due to subsidence due to mining for example). The site may then kept 'part full' for its recreation / amenity value (especially where regional water transfer has replace the need for the site for water storage).

If you have safe access to the site (one tried sampling some finer sediment sites where get back out became an issue), then it might be an idea to measure something relatively simple and build up a 3D picture of the sediment (allowing quantification of sediment loads during different periods) e.g. rod down to the base i.e. interface between underlying soil or rock and overlying sediment (depends on the scale of the deposits I guess) then measure volume susceptibility or Pb (or other elements) (via XRF) to link key features. Are there significant temporal and spatial variations? Where there a re few natural lakes then reservoir sites can provide environmental archives if used with caution.

In the past these site would have had monitoring records of rainfall, inflow, outflow and water levels. Not so common now.

I feel need to map palaeo geomorphology of the region. As you have GPR YOU CAN MAP 3D of sedimnets. Even shallow seismic works. Model for catastropic events , drainage incessions and discharge models.

Good luck

Zach,

I'd recommend running the typical suite of geotechnical analyses that are pretty much standard for commercial grading projects:

(http://www.geotechnicalinfo.com/geotechnical_laboratory_testing.html).

It might be useful to approach your sampling and subsequent analysis needs in a fashion similar to the sampling protocol that is used for standard reservoir investigations:

http://publications.usace.army.mil/publications/eng-manuals/EM_1110-2-4000_pfl/toc.htm

Working from the resultant delta(s) at the point of entry of the influent source(s)...it might be of interest to look at the change in sediment distribution and potential changes in chemistry (akin to a subsurface alluvial fan system -- proximal, medial, and distal).

Treatment of the area as a large hyporheic system might provide the specific needs for collection of samples for chemical analyses:

https://webspace.utexas.edu/alh2735/public/sawyer_et_al_hp_2009.pdf.

Hope this input is of some help...

All my best...

Greg

I think you can use ERT method with several geotechnical boreholes and combine the results together. after define motivation question for your study, you should design some methods for 3d reconstruction of alluvial sediments and bed rock morphology.

Dear sir,

Thanks for questions. Actually I am working in geomorphology (Rill and Gully Erosion in Badland topography, Lateritic areas). So, I used some standard Geo-technical parameters for assessing the rill and gully erosion.

Thanks for all.

Aerial photography, IR satellite, GIS based topographic studies / (paleo-)drainage study. The GPR will be useful if you´re looking for shallow bedrock and paleo-channels. But to help you we need to know what´s your final target: predicting a geomorphologic pattern, the evolution of the sediment infill over the paleo-reservoir etc...?

The GPR is a very coarse geophysical method, but probably the best for shallow structure; in addition to micro-gravimetry, geochemical mapping etc...

tl;dr: we need to know what you are looking for to give you advice on what approach to have precisely. The main point being to go from large spacial scale to detailed geochemical/technical studies if required.

As mentionned earlier, QGIS is quite a handy GIS tool (and free), and you can easily have satellite rasters.

First of all satellite image if available should be used for tone analysis .Analyzing S.I. will lead you to normal and ubnormal features and would ential you to define contacts between different lithostatigraphic units.In the next step a topographic map with relevant scale should be used to define if your area is located within a hydrographic,sedimentological or hydrologic basin....a basin-wise approach should be your focus.

In more advanced stage you need to define what stage of maturity your basin does represent by running what is known as hypsometric analysis,out of which you will be able to determine how much sediments are removed from your area.

Wow. Amazing advice everyone! You guys have definitely mentioned a few things I'd have never thought of, and have helped on improving the ideas that I had in mind already. I thank each and every one of you.

And Aurelien, I'm looking to gain as much possible data on restoring past reservoirs to their (as close as possible) natural physical, chemical and biotic stream states. I want to find out what tests gain valuable knowledge in order to make this natural restoration plan possible for future removals that can be similarly compared to the site I am studying. I realize that money is always a factor. But in order to find the most efficient and cost-effective (least expensive) methodology for dam removals, background data will be needed to construct a classification scheme for removal plans. I'm writing a master's thesis so I would like it to be a very inclusive and thoroughly assess all factors possible.

I thank you very gratefully for your advice.

read our paper Profiling of late Tertiary–early Quaternary surface in the lower reaches

of Narmada valley using microtremors prabhin et al. 2011. in J of Asian Earth Science v. 41 pp 325-334

When first making a geological study of an area, in my opinion the basic aspects to consider are: geological mapping, regional geology, structural geology, petrology, geochemistry and biostratigraphy. For more specific studies could also consider other related disciplines of geology, such as mineral resources, hydrogeology, geological hazards, volcanology, geophysics and others.

Ascertain the geology of the study area from the existing regional geological maps. Now you have two domains - the top sedimentary domain and a bottom basement domain. The sedimentary domain needs a sedimentological, hydrogeological, geotechnical, geochemical and morphological approach for study which I feel is your purpose of investigation to start with.

You have to plan your investigations in a very systematic way. Since the area marks an old reservoir site, you have to plan for studying sedimentological aspects in detail.

If you can lay your hands to retrieve pre-reservoir filling cross- sections of the study area from the archives, it is going to help you in understanding the original configuration of the reservor area and also the elevations at the bottom of the reservoir area. The repeat profiling along the cross-sections will give information about the sedimentation pattern in the reservoir. GPR survey will help you only if the depth is less than 20 m ,and therefore for getting the subsurface information you should bank upon seismic refraction survey followed by drilling. The drill cores are logged for interpreting sedimentation cycles and representative samples are taken for sedimentological anlysis and soil mechanical tests. The slopes around the reservoir rim are studied geologically and their sensitivity is adjudged.

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You can use satellite images as mentioned by one of the friend but actually two images from your study area in two different times e.g. Before and after this will be o help long with studying the cores. Plus in the incision of the river you will find possiblly good and helpful outcrops or clues

Also soil type is important and glacial history if important. Get out your compass clinimeter and start measuring dip and strike.

When we are carrying out geological survey, we cover every aspects of geology, topography, soil cover and nature of soil, drainage type and pattern and if possible nature of vegetation, which actually bears signature of geology. So geological survey is all inclusive and it depends on the surveyor which aspects should be her/his priority in that particular fieldwork but that does not mean the other aspects are less important or not significant.

When you carryout a survey, geologically the type of lithology (rocks and soil) has to be identified and mapped first. Then, the geomorphological features such as marshy land, barren land, presence of water bodies, human settlements, road and rail tracks etc. have also been studies. The structural features such as folds, faults, joints, lava traps etc. should be marked in your survey maps. The type of vegetation (water bearing plants, xerophytes etc) will give us an understanding about the area during the survey. The cultural and heritage sites shall be represented in the maps. For which Remotes sensing (satellite imageries) and GIS techniques may also be very helpful. Geological knowledge particularly petrology will give us useful information during the survey.

I think you have a treasure that will be most valued by sedimentologists, stratigraphers and environmentalists. The area also will be a laboratory for engineering geologists/ geotechnical engineers and hydrogeologists too. Biologists and isotope geochemists may also have some interesting aspects to study. The value of it depends on for how long the area had been under water. 50-100 years or more would mean that the area should be the subject of many thoughtful studies. If you could convince and coordinate with many scientists and work together with them it will be very beneficial to you compared to a lonely study of your own. May be that you would not see much of the bedrock exposures on which the sediments have been deposited. As suggested by many other folks before me, basic geology and mapping comes first. I suggest that you concentrate on several good stratigraphic sections that would be deep enough to be correlatable over a wider area. If you could do some good and accurate stratigraphic sections, your work would formulate the base to attract many other scientists of wider interests for you to co-work with. Good luck!