Low value of sedi_export as compared to usle_total

Hi all,
I am using the SDR model in an area where the dominated LULCs are forest, fallow and crop land. I am getting very low sedi_export value (about 0.3 Million ton ) as compared to usle_total (about 9 Million ton) . I have considered C values for forest, fallow and crop land as 0.001, 0.18 and 0.2 respectively and have considered P values as 0.5 for urban area and 1 for rest LULCs. I have checked the SDR value and found  maximum value as 0.21 and mean value as 0.04 which is very low. I think, the value of sediment_export is low due to low value of SDR if I am right. Any suggestion of how to increase the sedi_export (i.e. increase SDR if I am right) will be highly appreciated.

Thanks in advance.

Manas

Comments

  • PerrinePerrine Moderator, NatCap Staff
    Hi Manas, 

    Good thinking, it looks like it's the low SDR value that causes the low sed_export value. What this means it that of the soil eroded on the pixel (usle), only a small proportion reaches the stream.

    To change this proportion, you can use the calibration factors: k_b and IC_0. You can see the effect of a change in these factors in Figure 3 of the User's guide. From experience, we typically change one at a time (starting with k_b). Increasing k_b should increase the sed_export for low values. 
    Of note, changing k_b won't change the ranking of pixels in the watershed (i.e. the "hotspots" will remain hotspots) but it will shift all values up or down to match local knowledge.

    Best,

    Perrine

  • manasmanas Member
    Hi Perrine,
    Thank you very much for your response. Yes, I have changed the sed_export by increasing the K_b values and have noticed SDR is simultaneously increasing keeping IC_0 as 0.5. But in my study area the value of IC_0 varies from -1.0988 to -10.1607 with a mean of -5.636. I have noticed that a decrement in IC_0 value from 0.5,will increase the sed_export. but how taking IC_0 value as 0.5 is logical when it ranges from -1.0988 to -10.1607. Please help if my thinking is contentious.

    Thanks in advance.
    Manas
  • PerrinePerrine Moderator, NatCap Staff
    Hi Manas, 

    You are right, both k_b and IC_0. Unfortunately, it's still challenging to know a priori which one should vary to calibrate the model. 

    Again, referring to Figure 3, k_b and IC_0 have distinct effects on the SDR values:
    * changing k_b will increase or decrease the relative difference between the low-delivery and high-delivery areas; 
    * changing IC_0 will shift the whole distribution, without increase the contrast between low- and high-delivery areas.

    Without other information on the sediment dynamics in an area, we usually recommend changing k_b only; but there's no theoretical reason why you shouldn't change IC_0 too.

    Best,

    Perrine
  • manasmanas Member
    Hi Perrine,
    Thank you very much for your response. Now I am more interested in this model.

    Thanks.
    Manas
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