Bhaskar Sailesh - Go ahead with your plan of study. For a mixed research design, there is no need for collecting your data from two samples. You can use both the quantitative and qualitative designs on the same sample and only the approach is different. By using mixed research method you can well understand tourists poor behaviour towards beach cleanliness as well as the challenges faced by local communities. You can validate your findings using quantitative and qualitative data sources and use qualitative data to explore quantitative findings.

One of the key issues in mixed methods research is the integration of the results. If you use two different methods to study two different questions, and thus have little integration, then this would be considered a weak example of mixed methods.

As mentioned by @DavidMorgan having two research questions could be problematic. Perhaps you could develop an overarching question within which the other parts fit? Or focus on just one of the two questions.

I agree with David L Morgan . You have to look back at your research questions. Are those two a part of a bigger question? How do these two questions connect with each other? I recommend you to first research a bit about what is mixed-methods and the types of mixed-methods. Once you understand those, you should be sure for yourself if your approach make sense. Here are some useful dois:

10.1016/B978-0-08-044894-7.00287-6

10.1007/s11577-017-0454-1

10.1016/b978-0-08-097086-8.10550-1

I agree with David Morgan, A. S. Cohen Miller and Son Nguyen. You need to make sure that you are integrating and "mixing" your data to truly call your work mixed methods. Although it is acceptable to use multiple sources and focus on quant and qual approaches for each source, you need to make sure you're integrating the data for it to be considered mixed. If you want to answer your research question using both of these methods and do not intend to mix the data, think of calling your study "multi method" as it could be a more accurate term. Elizabeth Creamer does a wonderful job describing the differences here (Book An Introduction to Fully Integrated Mixed Methods Research

It appears that you aim to address the same broad topic (beach cleanliness) from 2 different perspectives, that of tourists and that of local communities. Hence, you have 2 research questions: 1) Why do tourists adopt a poor behaviour towards beach cleanliness? 2) What are the challenges faced by local communities regarding beach cleanliness?

Regardless of the study design you chose to answer each of these questions (quantitative or qualitative), I think that it is more important to clarify whether it is reasonable to include both questions in the same research project.

In your case, I think that first you need to provide a strong link between the 2 questions.

For example, it may be reasonable to design your topic guide for the qualitative part (2nd question) based on the findings of the quantitative part(1st question), but you need to be explicit the link between these 2 stages. If this is accomplished, I think that this could be a mixed-methods study with a sequential design.

You can validate your findings using two approaches.No need of collecting data from two different samples.Agree with David L Morgan

In my opinion if i got your point, you are going to collect your data from different sources of information for deeper understanding. So you could triangulate the data sources and data collection tools. For example: using both qualitative and quantitative study with tourists to understand their behaviour towards beach cleanliness, which called (Mixed method). In addition you could use qualitative study with the mangers or the head-leaders at their different levels to examine the facilitators and barriers. You have to hint and catch your ideas according to your main objectives while formatting your guidelines.

Dalia Hyzam There is quite a lot of debate about what the term triangulation means, to the extent that the editors of the Journal of Mixed Methods Research will no longer accept papers that claim to use triangulation as their motivation. In particular, there is a major distinction between comparing the equivalence of the separate results from two independent studies, versus using one set of results to add to or complement another set of results.

So, I would recommend avoiding this terminology and instead concentrate on the goals of the research.

I think we cannot call it a mixed research method

You certainly can, but like everything, it is dependent on the topic, your research methodology for the quant & qual sampling, and the purpose for each—the quant and qual. Speaking in generalizations, you can collect data from two different samples if they represent the same population. This may work if you have a “broad stroke” approach to your study. However, mixed methods studies are often not that simple. Many times, these data are collected temporally, one before the other. For example, qualitative data can be collected from a sample in order to have a deeper, richer, more detailed explanation for why a certain quantitative trend is occurring. Or, quantitative data is collected in order to measure trends quantitatively, or quantitative relationships, or generalizability, based on survey questions drawn from qualitative inquiry resulting data or theory. This can go either way. In many cases, it is argued then that the qualitative sample should come from within the quantitative sample, while in others you use the qual data/theory to develop your quant study (hypotheses, survey questions, etc...). Ask yourself the question on what you’re trying to achieve with each, or with both together. Again, it depends on what you are trying to determine with your research. I would offer the advice that, if you do use separate samples, one of the most important things is being transparent about it, explaining why and how these samples were used, and explaining how this approach strengthens or limits (strengths and limitations) the research.

It is usually called "triangulation" - I refer to it as "multiple and convergent methods" - the emphasis is on the word "convergent"........you can have two different audiences/target groups (multiple), but you must use the same questions (convergent)!

Many researchers have tried to classify and classify different types of research methods, and each of them has proposed different types of this research method.

You refer to this source:

Creswell & Clark (2007), Designing and Conducting Mixed Methods Research.

Yes, you can use a combination of the two ( quantitative & qualitative .)

Yes, you can collect your quan and qual data from different samples but if the results cannot be integrated it will not be appropriate to call it mixed methods.