Knowledge of sedimentation is required to determine the possible damages, amount of sedimentation in reservoir and erosion of watersheds.
In Karaj River erosion locations and sediment transport is an important factor in its watershed planning. In this paper modes of sediment formation and transportation, sediment and water flow interrelations and sediment variation of Karaj River are investigated and results are given.
The Karaj Cathment area is a part of the Alborz Chain. At a number of points in the upstream of the reservoir, steep ephemeral streams enter into the main river, and rather fans being formed as the heavy load main stream.
The typical of suspended-sediment transport curves can be apporoximated by the power relation:Q=LQn. 757 samples are plotted on the logarithmic graph paper as shown in figure 1, and its regression curve is as follows: Q = 0.37 Q244 in which Qs = suspoended - sediment discharge in tons per day, Q = water Discharge in m3/s., and L = a factor which can be taken a.s an index of relative erodibility. The exponent n is the slope of the curve on logarithmic paper measured in units of logarithmic cycles.
The annual suspended - sediment transport estimated from the mean daily discharge during the water years 1068 - 1976. From these eight samples, the regression curve is obtained by taking the annual suspended - sediment runoff in thousand tons p.a. as Y, and the annual water runoff in McM p.a. as X, (Fig. 2).
Characteristic curves for different types of storms can be defined and a composite sediment transport curve evolved.For example,the variation of sediment concentration for a particular rate of storm runoff hydrograph on Karaj River is shown in figure 4. Also figure 3 indicates the sediment variations for the year 1970 -71.
Eight years of suspended sediment measurements existed from the gauging station at Sira, but flow records for the Karaj River were available for longer period of time. Flow and suspended - sediment load were plotted against each other on a log paper for the years where both records were available. From this, an approximate relationship between flow and suspended sediment load was found. This relationship was used to estimate the suspended load for the years where only flow records existed. As a result nineteen years mean monthly suspended — sediment and flow of Karaj River are shown in figure
5.
)