I want to thank the two reviewers for their profound and very extensive and constructive comments.
It might be that these profound reviews let the authors respond in a particular detailed and profound manner. I was particular impressed by the detailed explanations regarding the number of isotope analysis in previous runoff geneation studies and the response regarding the question of semi-aridity of the region.
I think the paper has a clear potential to be published. I propose to follow the reviewer's suggestions as the author's have clearly proposed, too. I would like to see in the final manuscript the table about the number of events analysed in previous tacer studies on runoff generation. In addition, I'd like to see the explanations regarding the semi-aridiy of this region.

Kind regards and good luck,

A. Bronstert

Dear Authors,

being the handling editor of this manuscript, I now have the task to decide how to proceed with this submission. This is actually not an easy task, having the revised version on the desk and two reviews from well experienced reviewers. Those two reviews come to the maximum possible opposing conclusions: “Reject” (Rev. 1) vs. “accept as it is” (Rev 2).
First, I add the explanations from Rev.#2, which he added as “confidential to the editor” (probably he just did this accidentally).
“I recommend the publication of the paper in its actual form. Despite my concern during the first review about the reduced amount of samples analysed has not been solved (the authors have the samples they have and they cannot have any more) I consider that the authors have done a very profound review following the comments of myself and the second referee and the paper has improved greatly, especially concerning the introduction and discussion sections. For this reason, I think that the paper deserves to be published in HESS as it is.”
Second, I try to understand and assess the rather negative review from Rev # 1:
1) Criticism of the climatic classification of the Kaap Catchment. It is argued that the catchment is not semi-arid but semi-humid. Well, there is no very crisp and unique definition of semi-aridity.
Therefore, I had a look in Schulze et al, 1997, which is an excellent display of South African Agrohydrology and –climatology (though not cited in the paper neither the rview !). This is rather good in accordance with your figure 2 (which I find well placed). From this I can derive that in any month the pot ET is higher than the Precip. Therefore, one may keep the term semi-aridity. Of course it is sub-tropical, but his is not of major relevance. There are many possible peculiarities of semi-arid climate, even if rainfall is as high as 1000 mm /year. However, one can also derive that the small scale spatial variability of rainfall is high in this region, probably due to the distinct topography of this are.
2) Questioning if the hydrology should be treated “as a humid system (at least during the wet season)”. Well, again, there is no overall accepted standard (and no need) for a clear and crisp differentiation between humid and arid hydrological systems. Actually, many (but not all) hydrological systems have both dry and humid characteristics. Therefore, I do not see why this study should be not considered as a study in a semi-arid environment. I have been participating in semi-arid research myself, with conditions of rainfall as high as 800mm and pET above 2500mm. Groundwater contribution to streamflow (more precise: two-way interactions of alluvial groundwater and channel water) was an important mechanism for streamflow generation, of course during the wet season and at the beginning of the dry season. I definitely agree with Rev#1 that the processes an (therefore the validity of the results) do differ between the dry and the wet season
3) Questioning if the relatively sharp increase in runoff (“quick flow”) can be triggered at least partly by groundwater exfiltration. In case there is a hydraulic shortcut (preferential flow) between alluvial groundwater / shallow groundwater and channel system (and infiltrating rainwater and the shallow groundwater) this is a possible mechanism. There is ample of literature who reports on such specific investigations.
4) “blurred definition of the component ‘shallow groundwater’”. I agree, if groundwater is considered to be a major contributing source to runoff. It would be good to describe the groundwater system more in detail.
Therefore, taking into account BOTH recommendations from Rev.#1 and rev.#2 and my own inspections, my conclusions to the authors are: Please prepare a 2nd revised version of this manuscript, where you
• elaborate more on the climate of this catchment. Can you show or produce (from your data) a kind of Walther-Lieth diagram for one or two climate stations in that area?
• Discuss more on the general (semi-arid?) hydrology of this area. Can you show a “typical” hydrograph of the KAAP river (mean runoff, variations)? How many days without runoff/year? Include a new paragraph on the value of groundwater contributions for runoff
• Do you have any indications for quickflow contributions via the groundwater (i.e. indications of hydraulic shortcuts from infiltration to the GW-surface and further ahead towards the Channel?
Mentioned References:
- Costa, A.C., Foerster, S., de Araújo, JC., Bronstert, A. (2013): Analysis of channel transmission losses in a dryland river reach in northeastern Brazil using stream flow series, groundwater level series and multi-temporal satellite data. Hydrological Processes, 27, 1046-1060.
- Schulze RE et al. (1997) South African atlas of agrohydrology and climatology. Water Research Commission, SA

Best regards, A. Bronstert (handling editor)

Dear colleagues,

thank you for your moderate revision of the paper. However, there are still some open questions which must be dealt with:
1. First open question concerns mainly to your conclusion that you detected a "shallow groundwater" contribution in your hydrograph analysis. You derive this conclusion on the increased potassium concentrations. Thus, the question is: how can you discriminate between surface runoff and shallow groundwater runoff. Potassium can be termed a trace for quickflow, including surface flow.
2. It would help a lot if you can add some more explanations on the groundwater situation there, both deep (or “normal") groundwater and shallow (alluvial, perched?) groundwater. Do you have any data from gw-observation wells? If yes, please include such data in the paper. If no, you need to consider the possibility that the K-concentrations may be due to surface runoff.
3. Finally, If groundwater contributions (both deep and shallow) are that important, it would help the better understanding of the regional conditions, if you discuss and discriminate the different processes during the wet and dry periods of the annuals cycle. If I understood your study correctly, your tracing was performed (only ?) in wet season events. E.g. these processes would be rather similar to the ones in humid regions (as rev. # 2 pointed in his comments). This would require that you make this clear in the conclusions (e.g. you analyse rainy season hydrology in a semi-arid climate, etc.) and that you may discuss (or speculate?) what processes might be of importance for dry runoff generation. Obviously there is runoff in the dry seasons, even if this is small.

I hope that this ongoing discussion helps to further improve the paper and remain with best regards,

Axel Bronstert (handling editor of this manuscript)

All's Well That Ends Well.
kind regards,
Axel Bronstert