Predicting Discharge and Sediment flux of the Po River, Italy since the Last Glacial Maximum

Abstract

HydroTrend numerically simulates the flux of water and sediment delivered to the coastal ocean on a daily timescale, based on drainage-basin and climate characteristics. The model predicts how a river may have behaved in the geological past, provided that appropriate assumptions are made regarding past climate and drainage-basin properties.HydroTrend is applied to simulate a high-resolution discharge and sediment flux record for the Po River in Italy since the Last Glacial Maximum (LGM). A validation experiment of 12 years duration under present conditions shows a high correlation (r 2 = 0.72) with 12 years observed daily discharge. Monthly variations in simulated Po River discharge and sediment discharge for this same time period show an even closer agreement (r 2 = 0.97) with the observed data.Community Climate System models (CCSM) indicate that during the LGM the Po drainage-basin climate was much colder and drier than at present. The drainage basin itself was much larger due to a lower sea level. The Bølling period is shown to be an exceptional period in our model study, with significantly higher discharges and sediment loads, as glacier ablation was more dominant.HydroTrend simulations predict an average suspended sediment flux of 46.6 Mt yr −1 and an average bedload of 0.83 Mt yr −1 for the Po River during the Late Pleistocene (21-10 cal. kyr BP). This is ∼75% greater than in the Holocene (10-0 cal. kyr BP), where simulations indicate a suspended sediment flux of 26.7 Mt yr −1 and a bedload of 0.53 Mt yr −1 . The Würm Stadial simulations tend to show the highest suspendedsediment concentrations. However, when considering sediment yield where load is normalized to unit area (mass per square kilometre per time), simulations indicate slightly higher yield for the Holocene as compared with the Late Pleistocene, respectively 336 t km −2 yr −1 versus 283 t km −2 yr −1 , due to an increase in Holocene precipitation. Despite the overall lower yields during the Pleistocene, the model indicates that glacial influence is a dominant factor on the total sediment flux to the ocean.

Tectonic and climatic controls on knickpoint retreat rates and landscape response times

“…Analysis of sediment cores from ∼30 ka to present for the Lago di Mezzano and Lago Grande di Monticchio (which lie to the north and south of the study area, respectively) are consistent with a regionally significant cold and wet phase from 30 ka to 23.5 ka [ Ramrath et al , 1999], although precipitation was probably lowered at the LGM peak by ∼20% [ Jost et al , 2005]. Hydrological models for the Po River, northern Apennines, also support increased run‐off throughout this time period driven by spring melt of glaciers [ Kettner and Syvitski , 2008]. Moreover, sharply decreased infiltration due to the periglacial frozen ground conditions in the underlying carbonate bedrock has also been suggested during these glacial periods [ Giraudi and Frezzotti , 1997; Bogaart et al , 2003; Tucker et al , 2011], with the mean temperature of the coldest month being <−10°C at the LGM [ Allen et al , 2000].…”

Inferring denudation variations from the sediment record; an example of the last glacial cycle record of the Golo Basin and watershed, East Corsica, western Mediterranean sea

“…40 and 20 ka likely highlight this pattern of glaciers fluctuations in the Central Mediterranean area. Similar results by modelling of the Pô source to sink system shows that glacial processes are a dominant factor controlling the sediment flux to the ocean (Kettner and Syvitski, ).…”

Numerical modeling of cohesive sediments dynamics in estuaries: Part I—Description of the model and simulations in the Po River Estuary

“…At first, the initial temperature T 0 = 22.5 • C and zero sediment and salt concentration were set in the entire modeled area as, respectively, the initial sediment concentration and salinity (see [42]). An equilibrium distribution is achieved after about one-month simulation, and these values were re-applied as initial sediment, temperature and salinity to predict seabed evolution.…”

“…The axis of PRE is east longitude 12.05 • and north latitude 44 • 96667. The 75 000 km 2 river catchment of the Po is bounded at the North by the Alps with peaks over 4500 m, and at the south-west by the Apennines mountain chain with peaks generally less than 2000 m (more than a third of the drainage area (30 800 km 2 ) can be considered mountainous) [42]. It is the longest Italian river and goes through many important Italian towns, including Turin and (indirectly) Milan.…”

“…There is hardly any top set aggradation, most of sediment load is funneled to the offshore, about 16×10 6 tonnes/year, causing a high rate of fore-set propagation into the shallow northern part of Adriatic sea, while bed-load contributes only 2.5-5% of the total sediment output and high SSC. The monthly suspended sediment load was measured for the main distributary channels during six years field study [42], and may reach 300-400 mg/l in the main river stream (Panaro-Pilla) and in Tolle branch, while it is around 150-300 mg/l in secondary distributaries at South-Pilla and South-Tolle (see Figure 4). …”