Simulating sediment discharge at water treatment plants under different land use scenarios using cascade modelling with an expert-based erosion-runoff model and a deep neural network

Excessive sediment discharge in karstic regions can be highly disruptive to water treatment plants. It is essential for catchment stakeholders and drinking water suppliers to limit the impact of high sediment loads on potable water supply, but their strategic choices must be based on simulations integrating surface and groundwater transfers and taking into account possible changes in land use. Karstic environments are particularly challenging as they face a lack of accurate physical descriptions for the modelling process, and they can be particularly complex to predict due to the non-linearity of the processes generating sediment discharge. The aim of the study was to assess the sediment discharge variability at a water treatment plant according to multiple realistic land use scenarios. To reach that goal, we developed a new cascade modelling approach with an erosion-runoff geographic information system (GIS) model (WaterSed) and a deep neural network. The model was used in the Radicatel hydrogeological catchment (106 km2 in Normandy, France), where karstic spring water is extracted to a water treatment plant. The sediment discharge was simulated for five design storms under current land use and compared to four land use scenarios (baseline, ploughing up of grassland, eco-engineering, best farming practices, and coupling of eco-engineering/best farming practices). Daily rainfall time series and WaterSed modelling outputs extracted at connected sinkholes (positive dye tracing) were used as input data for the deep neural network model. The model structure was found by a classical trial-and-error procedure, and the model was trained on 2 significant hydrologic years. Evaluation on a test set showed a good performance of the model (NSE = 0.82), and the application of a monthly backward-chaining nested cross-validation revealed that the model is able to generalize on new datasets. Simulations made for the four land use scenarios suggested that ploughing up 33 % of grasslands would increase sediment discharge at the water treatment plant by 5 % on average. By contrast, eco-engineering and best farming practices will significantly reduce sediment discharge at the water treatment plant (respectively in the ranges of 10 %–44 % and 24 %–61 %). The coupling of these two strategies is the most efficient since it affects the hydro-sedimentary production and transfer processes (decreasing sediment discharge from 40 % to 80 %). The cascade modelling approach developed in this study offers interesting opportunities for sediment discharge prediction at karstic springs or water treatment plants under multiple land use scenarios. It also provides robust decision-making tools for land use planning and drinking water suppliers.

Dynamic Assessment of the Flood Risk at Basin Scale under Simulation of Land-Use Scenarios and Spatialization Technology of Factor

Climate change, population increase, and urban expansion have increased the risk of flooding. Therefore, accurately identifying future changing patterns in the flood risk is essential. For this purpose, this study elaborated a new framework for a basin scale that employs a future land-use simulation model, a factor spatialization technique, and a novel hybrid model for scenario-based flood risk assessment in 2030 and 2050. Three land-use scenarios (i.e., natural growth scenario, cropland protection scenario, and ecological protection scenario) were set and applied in Jinjiang Basin to explore the changes in future flood risk under these scenarios. The results indicate the different degrees of increase in flood risk that will occur in the three scenarios. Under the natural growth (NG) scenario, the city will expand rapidly with the growth of population and economy, and the total area with high and very high flood risk will increase by 371.30 km2 by 2050, as compared to 2020. However, under the ecological protection (EP) scenario, woodlands will be protected, and the growth in population, economy, and built-up lands will slow down with slightly increased risk of flooding. In this scenario, the total area with high and very high flood risk will increase by 113.75 km2 by 2050. Under the cropland protection (CP) scenario, the loss of croplands will have been effectively stopped, and the flood risk will not show a significant increase under this scenario, with an increase by only 90.96 km2 by 2050, similar to the EP scenario. Spatially, these increased flood risks mainly locate at the periphery of existing built-up lands, and the high-flood-risk zones are mainly distributed in the southeast of the Jinjiang Basin. The information about increasing flood risk determined by the framework provides insight into the spatio-temporal characteristics of future flood-prone areas, which facilitates reasonable flood mitigation measures to be developed at the most critical locations in the region.

BEBERAPA SKENARIO PENGGUNAAN LAHAN UNTUK PERBAIKAN KONDISI HIDROLOGI DI DAERAH ALIRAN SUNGAI CIDURIAN (Land use scenarios for hydrological conditions improvement in Cidurian Watershed)

Daerah Aliran Sungai (DAS) Cidurian merupakan salah satu DAS di Pulau Jawa dengan kategori sebagai DAS yang dipulihkan. Kinerja DAS Cidurian secara umum dari hulu sampai dengan hilir termasuk dalam klasifikasi kategori buruk. Penelitian ini bertujuan untuk 1) mengkaji karakteristik hidrologi DAS Cidurian menggunakan model hidrologi SWAT; 2) mengkaji kinerja hidrologi berdasarkan skenario simulasi yang disusun; dan 3) menyusun strategi keberhasilan Rehabilitasi Hutan dan Lahan pada DAS Cidurian berdasarkan skenario terbaik. Berbagai skenario penggunaan lahan dan pengelolaannya diujicobakan menggunakan model SWAT (Soil and Water Assessment Tool) untuk menduga dampak penerapannya terhadap karakteristik hidrologi pada DAS Cidurian. Skenario yang diaplikasikan adalah sebagai berikut: 1) Implementasi RTRW (Rencana Tata Ruang Wilayah) Provinsi Banten dan Jawa Barat; 2) Implementasi Rehabilitasi Hutan dan Lahan dengan penanaman penanaman vegetative dan; 3). Implementasi Rehabilitasi Hutan dan Lahan penanaman vegetatif dan Konservasi Tanah dan Air secara vegetatif dan sipil teknis. Kalibrasi dan validasi dari model menunjukkan kategori memuaskan dengan nilai NSE (Nash-Sutcliffe Efficiency) 0,53 dan 0,50. Semua skenario menunjukkan peningkatan respon hidrologi dibandingkan dengan kondisi eksisting tahun 2020. Ketiganya memberikan respon limpasan permukaaan dan hasil sedimen yang menurun serta aliran lateral dan aliran dasar yang meningkat. Semua skenario ini menurunkan nilai Koefisien Aliran Tahunan (KAT) dan Koefisien Regim Aliran (KRA). Skenario penerapan kombinasi Rehabilitasi Hutan dan Lahan penanaman vegetatif dan Konservasi Tanah dan Air menjadi skenario terbaik dengan nilai KAT 0,27 (kategori rendah) dan KRA 22,40 (kategori rendah).

Response of Runoff to Extreme Land Use Change in the Permafrost Region of Northeastern China

To study the response of runoff to extreme changes in land use, the Soil and Water Assessment Tool (SWAT) model was used to construct historical, extreme, and future scenarios for several major landscape types in a permafrost region of northeastern China. The results show that the SWAT model is applicable in the Tahe River Basin; forestlands, shrublands, wetlands, and grasslands are the main land-use types in this basin, and the transfers among them from 1980–2015 have impacted runoff by less than 5%. Under extreme land use-change scenarios, the simulated runoff decreased from grasslands, to wetlands, shrublands, and finally, forestlands. The conversion of extreme land-use scenarios produces different hydrological effects. When forestland is converted to grassland, runoff increases by 25.32%, when forestland is converted to wetland, runoff increases by 13.34%, and the conversion of shrubland to forestland reduces runoff by 13.25%. In addition, the sensitivity of runoff to different land-use changes was much greater during flood seasons than in dry seasons. Compared to the reference year of 2015, the annual simulated runoff under the two future land-use scenarios (shrublands to forestlands and shrublands to wetland) was less. Also, both future land-use scenarios showed effects to decrease flooding and increased dryness, This study provided important insight into the integrated management of land use and water resources in the Tahe River Basin and the permafrost region of northeastern China.