Rainfall Simulation to Estimate Potential Sediment Loadings to the Albuquerque North Diversion Channel

Runoff from high-intensity short-duration thunderstorms is a major hydrologic phenomenon in the southwestern United States. If the runoff is excessive, flooding with concurrent damages may result. Exacerbating the flood hazard is simultaneous sediment transport with the runoff water. When the sediment-laden flow enters a constructed channel it may exceed the water-only design capacity or the sediment in the flow may deposit to such an extent that the channel no longer can contain the water-only flow adequately. Either situation reduces the frequency or return period design flow which the constructed facilities can accommodate.

Estimating the amount and characteristics of the sediment being transported in the channels requires an understanding of the material reaching the channels from upslope sources. In this study, rainfall simulation was used to measure runoff and sediment yields from three sites in the drainage basin of the Albuquerque North Diversion Channel. Nine 1m x 3m plots were studied and simulated rainfall was applied under “dry” and “wet” antecedent soil moisture conditions for a total of 18 plot-runs. One plot was scraped bare at each of the three sites to simulate disturbance caused by clearing and construction activities. The other plots were sampled with the natural vegetation at the site intact.

Steady-state infiltration or loss rates ranged between 3 and 69 mm/hr (0.12 and 2.72 in/hr) for the dry runs and between 18 and 42 mm/hr (0.71 and 1.66 in/hr) for the wet run experiments. Sediment yield per area per unit of runoff can be used to estimate sediment loading to a channel once runoff is modeled. Study results indicate that a value of 50 kg/ha/mm of runoff (0.52 tons/acre/in of runoff~ is reasonable for undisturbed plots and that 300 kg/ha/mm (3.12 tons/acre/in) is reasonable for plots which were scraped bare of vegetation. The deposited sediments had median grain diameters comparable to the surface soils at the sites, but the gradation coefficients were lower for the sediments indicating that the finer particles were eroded preferentially from the plots. The ratio of deposited sediment yield to total sediment yield averaged 61%, with a wide range from 20% to 94%. Manning’s n values, as determined from hydrograph analyses, averaged 0.453 ml/3/s (geometric mean of 0.231 ml/3/s) with a very wide range. Study results should be very useful for hydrologists and erosion and sediment-transport modelers conducting drainage analyses in the Albuquerque area and other southwestern cities.