*2.4. Sediment Rating Curves*

The SRC method is based on an empirical relationship between the discharge and the sediment concentration/load. Likewise, the collected suspended sediment concentration samples were converted into suspended sediment load (SSL) in t/day and related to their corresponding discharges in m3/s to develop the rating curves, encompassing low and high flow conditions. Additionally, 10% bed load was added to the suspended load as recommended by [10]. Total load equations (Equations (1) and (2)) are expressed in the form QT =aQb, where QT is sediment discharge in t/day; Q is water discharge in m3/s; and a and b are constants as solved on page 15 of [3]. They were entered as upper boundary conditions in the model and depicted graphically in Figure 4.

$$Q\_T = 1.686 \times 10^{-4} \,\mathrm{Q}^{2.627}, \text{ for } Q \text{ >} = 481 \text{ m}^3/\text{s} \tag{1}$$

$$Q\_T = 4.474 \times 10^{-32} Q^{12.868}, \text{ for } Q < 481 \text{ m}^3/\text{s} \tag{2}$$

where *QT* = total load (suspended + bed load) in t/day with respect to flow discharge Q in m3/s.

**Figure 4.** Sediment rating curve.

The annual load calculated by SRC was 212 million tons (Mt). The calculated monthly loads are shown in Table 3 and Figure 5. As can be seen, most of the sediment transport processes took place in the summer months. Against 84% of the annual flow, 98% of the sediment load transport occurred from May–September.

**Figure 5.** Monthly sediment load at Besham Qila with sediment rating curves (SRC).


