A Study of Sediment Budget of the Yellow River Delta: The Case of Diaokohe Lobe

Abstract

Sediment dispersal at the river mouths has been an important topic in the fields of geomorphology and hydraulics for a long time and estimating sediment budget of the deltas is a principal method for quantifying the sediment dispersal system at many river mouths. Many reports about sediment dispersal at the Yellow River mouth have been given previously using this method. However, since the dry bulk density of deposits in the delta and the boundaries set for calculating the volumes of deposits did not receive a proper treatment, big discrepancy existed between estimates of sediment budgets of the delta provided by the previous studies.Considering the effects of grain size composition, burial depth, and exposure conditions on the dry bulk density of deposits and based on abundant data about the dry bulk density of deposits in the delta, this study defined the dry bulk densities for the deposits in the delta plain and buried delta front deposits, buried prodelta, exposed subaqueous prodelta, and newly deposited top 1 m layers on the delta front. Combining the constructed models of dry bulk density for different depositional settings with the results of analyzing the sedimentary framework of the delta, sediment budgets at Diaokouhe lobe of the Yellow River delta were calculated. The foot of the delta front slope was set as the outer margin of area for defining the sediment budgets. This margin is of geomorphologic significance and is easy to be located on the surface of delta recorded by the bathymetric data. Results show that sediment deposited in the delta plain and front of the Diaokouhe lobe over the period from 1965 to 1974 was about 7.10×10 9 tons, accounting for 73.5% of the incoming sediment. Errors resulting from ignoring clay layers in the deposits on delta plain and front, consolidation of soft layers underlying delta deposits, and deviations in records of the incoming sediment were proved to be about 2.6% for the percentage of sediment deposited in the delta, suggesting the higher reliability of the sediment budgets given by this study. From the mass and volume of sediments deposited in the Diaokouhe lobe over the period of 1965 -1974, a mean dry bulk density of 1.36 g/cm 3 was acquired. On account of the dominance of silt in the deposits of the delta, it seems to be an appropriate approximation of the mean dry bulk density for the deposits in the other lobes of the delta.

以往在黃河三角洲沉積量的估算中 ,對沉積物干容重和計算邊界等問題不夠重視 ,導致計算結果存在明顯出入。本項研究通過廣泛收集資料和大量采樣分析得到了多種沉積環境下沉積物干容重的計算模型 ,結合三角洲沉積結構分析和利用地形測量數據 ,計算了黃河口釣口河流路時期亞三角洲不同時期的沉積量。其中 196 5年至 1974年間釣口河亞三角洲前緣坡腳以內的總淤積量為 71. 0億t。其平均干容重為 1. 36g/cm3。這一干容重用于估算其它亞三角洲沉積量不會造成明顯誤差。認為忽略三角洲下松軟沉積層的壓實沉降、三角洲平原相和前緣相中粘性土與非粘性土干容重的差別以及來沙量的測量誤差對計算結果影響較小。