How to obtain a job in Geology/Geography /oceanography/meteorology departments

You are an engineering graduate and you are eligible to apply for many openings in our country in various industries directly or indirectly related to your core qualification which is civil engineering. The disciplines like Geology, Geography, Meteorology etc are specific areas and for the students who have a degree in that can apply in departments and organisations related to that. So for you, the scope of applying to them will be limited to the civil engineering role in those departments in association with their main activity in the above-mentioned disciplines. That is one possibility of entering those organisations and later by acquiring additional qualifications in the niche areas one can try for a lateral shift in the same organisation. Many people have planned like that and have become successful in getting the job of their choice.
Right now you have one option and that is to acquire a specific diploma through some reputed online institute in the area of your interest and then apply for the posts where essential qualification is not mentioned as a degree in the specific areas that you have mentioned as your interest areas. There are many online agencies like Coursera, Unacademy, edX, Lynda, Udemy, Alison, MIT open courseware etc which impart training in various areas including the ones mentioned by you.
Another option which is a lengthy process but has its own merit is to go for a PG in the area of your interest and then apply for the executive cadre posts directly or through competitions and get a job in those departments and organisations in our country where the main area of their operation is linked to above subjects.
Just as an example, for Geology qualified person organisations like Reliance Industries, ONGC, Shell, Wipro, Cairn Energy etc are there for trying to pursue a job. Another example is that of Geography where organisations like Survey of India, Statistical and Map organisations, Institutes where cartographers are needed etc have scope for getting a job. Cartographer position is available in almost all the higher education colleges (UG and PG) in our country.

You are a civil engineering graduate. You want to work in Geology and Geography. Civil Engineering subject is related to some extent to Geology and Geography. One of my friends who completed his M.Sc in Geology later joined as a research scholar in the Civil Engineering department of IIT, Delhi and worked in the public health department and became a professor there. There are civil engineers who are working in ONGC and other companies where Geology is the main subject required.
There are organisations which deal with geology but will have openings for civil engineers also. ONGC is one such organisation. There are many openings for graduate engineers in this organisation and Civil engineers are also eligible for this. Similarly, the coal mining companies and other mining companies will also have openings for civil engineers even though their major operation area is geology and mining. Many cement factories will also have their mining activities and they will also recruit civil engineers. So try for a suitable post in any of the above fields so that you will have an interest in the work there.
There are many diploma courses available in the field of Geology and Geography. While trying for a job in the areas mentioned above, you can do a diploma course in Geology or Geography. That will enhance your chances to get a job in the related fields.
Civil engineers will have plenty of chances in Environmental sciences also. You can do a certificate course in this discipline and that will enhance your chances to get a job in your area of interest. All the mining companies will have their own environmental engineers.

Since you have already acquired the degree in Civil Engineering and this should suffice your purpose for absorption in the different departments in the private sectors apart from Public Undertakings such as ONGC, Coal India Ltd, Cement Industries etc.
while considering your prospects in the different organisations, you need to consider such organisations where there is the application of Geology as well in their organisations. ONGC and Coal India, NMDC can offer you such responsibilities provided you show your inclinations for such assignments.
ONGC and Coal India have their fields of mining, survey and forestry and such they would have immense benefits with such Civil Engineering Graduates having their interest on earth and science apart from their interest for mining explorations. All such assignments are related to Geology and depending upon the interest of the aspirants, they might be put in the Geological Departments so as to enhance their knowledge in Structural Geology, Mineralogy, Geomorphology etc. Your exposure in these areas could enhance your promotion prospects in the Geological Departments. While going through such Diploma Courses through your self studies would involve additional timings apart from getting your late recognition in this field. Hence you should think prudently how best your are encashing the present qualification with the exposure of Geography and Geology in the same organisation where there is the application of other fields such as Geography and Geology apart from Civil Engineering. While doing so, you are saving your time to understand these fields. Your value naturally enhances with your experience earned in this field.