Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering ConferenceShanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Investigation on Geomorphological Evolution in a Lagoon Dominated by Increasing Runoff
Jiadong Fan 1, Cuiping Kuang 1,*, Zhichao Dong 2,*, Xin Cong 1, Xuejian Han 1
1 College of Civil Engineering, Tongji University, Shanghai, China.
2 Tianjin Port Engineering Institute Co.,Ltd. of CCCC First Harbor Engineering Co.,Ltd, Tianjin, China.

Lagoon provides a great habit for wild animals, but it is also faced withthe risk of increasing runoff. In our recent research, we revealed thatrunoff dominates the water exchange in Qilihai Lagoon without any ice
cover (Kuang et al., 2020). Zhou et al. (2014) emphasized thatgeomorphological evolution is dominated by both runoff and tide. They
took the combined influence into account, and investigated that by athree-dimensional numerical model. The results indicated that runoff has
great effect on the development of tidal channel and ebb delta. Similarly,
Silvio (2010) investigated the long-term evolution of a tidal lagoon, andpointed out that the advective sediment transport is dominated by bothrunoff and ebb tide. In addition, runoff would intensify the erosion
capacity, and enhance the ebb-directed sediment transport in a fluviodeltaic system (Guo et al., 2015). Min et al. (2019) investigated thesediment transport caused from large runoff in Curonian Lagoon,Lithuania. Based on the numerical simulation, they revealed that extreme
storm events would bring about much more sediment output. Moreover,
the results of the long-term simulation showed that approximately 62%
sediment input from the upstream rivers would settle in the lagoon.

ABSTRACT
Nowadays, climate changes result in frequent heavy rainfall, andincreasing runoff would alter the initial equilibrium state of a lagoon. To
figure out the geomorphological evolution in Qilihai Lagoon caused
from increasing runoff, an ideal model is established for simulation. The
findings are as follows: 1) With increasing runoff, tidal creeks areenlarged in both width and length; 2) The tidal creeks would extend tothe river mouths once the runoff is over the record; 3) Enhancing widthof tidal creeks would combine the tidal creeks together; 4) The
deposition amount descends while the erosion amount increases withincreasing runoff.

KEY WORDS: Numerical modelling; runoff; geomorphologicalevolution; Qilihai Lagoon.

INTRODUCTION
Nowadays, with climate changes, extreme rainfall occurs more and more
frequently. The regional short-term heavy rainfall is likely to cause theflood in a water basin. The influence resulted from flood would affectthe downstream and the estuary. A lagoon system is usually generated ina semi-closed estuary and has great ecological benefits (Barbier et al.,2011). In previous study, Kim et al. (2002) found that both rainfall andurbanization would increase the annul runoff in the Indian River Lagoon
watershed, Florida. It is clear that, besides heavy rainfall, humanactivities also have influence on the hydrodynamic conditions to alagoon. For the development of coastal zone, human activities, involving
land reclamation (Breber et al., 2008; De Pippo et al., 2004), dredging(Taylor, 2012) and relocating estuary, would alter the initial equilibrium
state of a lagoon, and the new hydrodynamic condition would bringabout the geomorphological and ecological evolution. Fortunately,ecological restoration of lagoon provides an effective approach to protect
the coasts from deterioration (Leruste et al., 2016; De Wit et al., 2017;2020). In general, it costs approximately 20 years to restore theecological stability, but the previous influence is irreversible, so neitherhydrodynamic conditions nor geomorphological conditions would berestored to the initial (Spencer et al., 2017; Chen et al., 2020).

In this paper, we aim to figure out the influence of increasing runoff on
geomorphological evolution in a lagoon. Qilihai Lagoon would beselected as the subject for its typical geomorphology. For investigation,
an ideal model of Qilihai Lagoon would be established by MIKE21, setwith the simplified parameters according to the field survey. Then, an
appropriate range of increasing runoff would be set based on themaximum mean annual runoff for simulation by a single variable method.
Moreover, erosion amount, deposition amount and net erosion amountwould be focused for quantitative analysis. The findings would providea reference for predicting the evolution of a lagoon under increasing
runoff in the long term.

METHODOLOGY
Numerical Model
Nowadays, MIKE is widely used in researches on hydrodynamics,
sediment transport, particle tracking in coasts, estuaries and lakes (Lianget al., 2017; Soudi et al., 2019; Kuang et al., 2020). In this study, bothhydrodynamic module and sediment transport module in MIKE 21 FM
are utilized to simulate the geomorphological evolution of the ideal

As the largest lagoon in Northern China (Xing et al., 2019), Qilihai

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