The Effect of Soil Tillage Equipment on the Recharge Capacity of Infiltration Ponds

Round 1

Reviewer 1 Report

 

Comments for the paper entitled: The Effect of Soil Tillage Equipment on the Recharge

Capacity of Infiltration Ponds

 

This paper can be classified as a technical and informative. The quality of this paper can benefit an introduction and discussion on ponds infiltration rate in conjunction with the larger scale as well as environmental concerns.

Many important facts in the paper are mentioned without referring to a reference and/or without quantitative values.    

Introduction:

The introduction is well written and informative. However, quantitative data is missing as well as references for some of the facts and/or data that were mentioned.  

L42: “many years” – please be specific

L42-L53: this paragraph contains a lot of important information without any reference.

L74: “MAR” – was not defined

 L75-76: “significant decrease in the recharge capacity during the winter months was observed and in amounts that can explain much of the annual volume losses.”

Please quantify; from? to? and the amounts.

Materials and Methods

 L171: calculations of infiltration rate

Is the drop in water level between t-i and t-d is linear? If not, Eq. 1 is inaccurate.

Please add some measured data of water level as function of time from which you have calculated the infiltration rate.

You may want to use the “falling-head” equation that account for the exponential decay nature of the water level drop under falling head conditions. The falling head equation allows you to calculate the saturated hydraulic conductivity which is also what you are quantifying by Eq.1 if the water flow is under saturated conditions.  

Please improve the presentation of  Eq. 1 and Eq.2

L183: “Continuous infiltration rate” – please explain “Continuous”

Fig 4: statistical analysis is missing

Discussion

Throughout the paper and discussion it is not clear what the governing mechanism is: enhancing porosity or pore size? Faster drying, mixing the crust with dipper layers? In my opinion only the removal of the bio-crust cannot fully explain the results – since, as mentioned, it was done before .

Please discussed the potential effect of shorten drying phase and soil tillage on water quality.

Conclusions:

L273: “complete drying” – to what depth? How do you quantify the complete drying; did you measure the water content or matric potential in the soil profile?  

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

Author Response

Please see attached file

Author Response File: Author Response.docx

Reviewer 2 Report

The Yavne infiltration of the Shafdan effluent is world famous and a good example of the reuse of treated effluent. Writers describe to a large degree of detail the investigations aimed at determining the optimal soil tillage that removes the clogging or blockage of the infiltration basins and the results of these investigations. The operations are not scraping and removal of the crust or clogging material. In fact it is mixing of the filtered sediments (present in the treated effluent) with the subsoils’ sediments in the floor of the basins. The writers realize and describe that the blockage is complicated and depends on many aspects: effluent quality, drying periods, seasonal effects.

The deployed methods of soil tillage differ in working depth in the ground. Probably the depth of tillage determines the depth of the compacted layer. As a reader, it is unclear whether the positive effect of the subsoiler is not mainly or entirely due to the greater working depth. The filtered sediments present in the effluent in the long term accumulate in the processed top layer. Could it be that after a few years of applying the new method, its positive effect diminishes or even disappears? The paper would increase in value even more with a consideration of the effect in the long term.

Minor detail: the writers sometimes use the abbreviation MCM/year and sometimes Mm3/y. And it would help if it was clarified that in equation 2 the number 100 converts an infiltration rate of meters per hour into centimeters per hour.

Author Response

Please see attached file

Author Response File: Author Response.docx

Reviewer 3 Report

It would be useful to show data supporting the statement that recharge capacities had declined over the 2015-17 time period.   In line 64, it is stated that the role of the drying period is to "enable aeration of the soil and to maintain constant infiltration rates."  According to Reference 12 (Bouwer, 2002), drying of basins is to allow the clogging layer to dry, decompose, shrink and crack (page 130).  More explanation is warranted here.   In Line 81, the term non-academic operational reports is used.  This is a term I am not familiar with.  I suggest re-wording this sentence.   In Section 3.2, Soil Compaction, it is noted that there was a "compacted layer" at 30 cm depth.  Is this based on high measurements within a specific depth interval at 30 cm or based on reaching the maximum pressure of 200 psi at 30 cm?  After using the subsoiler, this "compacted layer" is extended to a depth of 50 cm.  Is it possible that the natural compaction of the sediments is 200 psi below the depth of disturbance?  I suggest additional data be presented here to understand how compaction is being defined and how it varies in the soil profile.  The way it reads now, the implication is that the heavy equipment and lack of drying between cycles formed a compacted layer. While this may be true, additional data needs to be presented to support this.  Building on the soil compaction section, Bouwer, 2002, on Page 129, discusses the potential of fine particles to migrate downward.  Is there any possibility that this mechanism is at work as well as compaction with heavy equipment?    Line 249 appears to really nail the problem due to conducting tillage operations when the basin sediments were not dry and even wet.  In Orange County, we take great pains to make sure the basins are completely dry, which can take 1-3 weeks, before they are disturbed.   Line 276.  Bouwer, 2002 recommends grading basins to be as smooth as possible before re-wetting. Orange County uses a motor grader to grade the bottoms of the basins before they are re-wetted.  This may be something to test.  The concern is that over the long term, the clogging materials are building up in the soil profile and being redistributed but will reach a critical mass and greatly reduce infiltration rates.  A site here in Southern California continuously discs the basins until they reach a point of no return.  They then over-excavate the upper 1-2 feet of sediment and clean it using a sand wash plant, place it back in the basin, and start the process over again. 

Line 93: grammar—change “then” to “than”

Line 99: specify/ add more detailed explanation of soil compaction processes

Lines 176-180: what is the historical/ baseline soil compaction throughout the basins? Provide more data/ figures here to better characterize compaction.

Line 259-261: add more explanation/ data to prove the statement.

 

Author Response

Please see attached file

Author Response File: Author Response.docx