## 3 Materials and Methods  
This study focuses on documenting and dividing the Quaternary braided river sedimentary architectural structure in the Songyuan region and establishing a three-dimensional sedimentary model based on elements to predict the structural characteristics of braided river systems. The study area is located in Dongdenglouku Village, Ningjiang District, Songyuan City, Jilin Province, in northeastern China. The Quaternary strata in the study area are selected because the sedimentary and paleoflow characteristics of the strata indicate that the braided rivers in the Matsubara region are typical coarse sand/gravel bedded deposits (planform) [8,28]. Within a small range of 4 km\({}^{2}\), a good number of sections show excellent exposure in different directions, ensuring that detailed fluvial architectures of the braided river can be captured in 3 dimensions. To achieve this goal, this study mainly adopted the hierarchical analysis approach, considering the sedimentary processes, scale, and temporal context [7,8,33,34], to conduct a detailed analysis of 10 sedimentary outcrop profiles exposed at four sites in the study area. All of the outcrops were photographed from the ground, and the architectural panels in this paper were constructed from merged photographs. A handheld global positioning system (GPS) device was used to determine the locations, strikes, and dips of sand bodies. The exposed stratigraphic profile of the study area was described and interpreted with a thickness of 8-15 m and a total length of 1800 m. Based on the characteristics of grain size and sedimentary structures, the lithofacies were divided following the classification standard of [PERSON] [37] (1978). Then, according to the observations of genetic facies associations and the recognition of key stratigraphic surfaces, different architectural elements were defined to complete the interpretation of the corresponding sedimentary environment [38,39], and the external geometric features and the contact combinations between the architectural elements were observed and measured in detail. Paleocurrent orientations were measured from unidirectional sedimentary structures, mainly trough and planar cross-bedding [3]. The hydrological data collected from the Second Songhua River Fuyu hydrological observation station (1955-2007) were applied to verify the climatic environment of the research area. Parameters such as the bankfull channel depth (d), mean bankfull channel depth (d\({}_{\text{m}}\)), and bankfull channel width (W\({}_{\text{b}}\)) are often used to quantitatively characterize the scale of ancient fluvial systems [5,25,40]. In this study, we measured the above parameters as well as the average bar thickness (d\({}_{\text{bm}}\)), maximum bar thickness (d\({}_{\text{bm}}\)), bar width (W\({}_{\text{bar}}\)), and single-channel width (W\({}_{\text{c}}\)) (Table 1). All measured thickness values considered the 10/9 correction for diagenetic compaction to compare with the empirical formula for modern rivers [5]. Meanwhile, for the measurement of the thickness of a single river channel and bar, considering the erosion after deposition, the highest point could be identified as the top interface of the sediment. Certainly, the case of relatively severe erosion was excluded from the measurement. The height from the deepest point at the channel bottom to the top of the deposit is d, and the distance between identifiable single-channel edges is measured as W\({}_{\text{c}}\). Generally, the shape of the channel is considered lenticular with a flat top, so the vertical height between the bottom boundary and top interface of the channel is measured every 0.5 m within the width of a single river, and the average value is then calculated to obtain d\({}_{\text{m}}\). The distance between identifiable bar edges is measured as W\({}_{\text{bar}}\).