Study On The Interconnected River System Network In The Water Diversion Project From The North Canal To Langfang City

The distribution and connectivity pattern of river and lake systems affect the regional water resources allocation and the stability of ecological and environmental systems.Langfang has been exploiting underground water for years,which is seriously short of water resources,and uneven river runoff.The Xianghe reach of the North Canal is abundant in water,but the river in the urban area is severely cut off.In this paper,the North Canal-Yongding river of Langfang city is taken as the research area.Aiming at the current problems of extreme scarcity of water resources,unbalanced spatialtemporal distribution and insufficient ecological water using in the water system,three schemes of the interconnected river system network are proposed.The first scheme is to divert the main water conveyance channel in the water diversion project of the North Canal-Yongding river of Langfang city.The second scheme connects the inner ring channel of urban area on the basis of the first scheme,and the third scheme connects the outer ring channel of urban area on the basis of the second scheme.Finally,the recommended scheme of the interconnected river system network is obtained by comparing and analyzing the morphological characteristics,structural connectivity and hydraulic connectivity of water system,to realize the interconnection and interoperability of the main river systems of the North Canal-Yongding river regional water network in Langfang city.(1)Based on the graph theory,the water system connectivity of different schemes in the study area was quantitatively analyzed from the perspective of water system structure connectivity.Therefore,the third scheme has the best river confluence and the highest degree of network;the second scheme has the second river confluence and the second degree of network;and the first scheme has the worst river confluence and the lowest degree of network.(2)Based on the theory of water system hydrodynamics,1-D hydrodynamic mathematical models are established for three schemes respectively.From the perspective of water system hydraulic connectivity,hydrodynamic numerical simulation is carried out for different water system connection schemes in the study area,and the water depth,flow rate,flow rate and drainage capacity of the river are analyzed.All the connection schemes can realize the connection between the North Canal to Yongding River in Langfang city.Under the same upstream flow boundary,water exchange can be realized in all river sections of the connection schemes,and the water depth,flow rate and flow velocity are moderate.In the scheme,the water depth of each reach is similar,and the discharge meets the minimum ecological water quantity of each reach.The check of drainage capacity of Longhe River can meet the standard of once-in-50-year drainage.(3)Based on the evaluation theory of water system connectivity,10 evaluation indexes were selected from the three aspects of water system connectivity morphological characteristics,water system structure connectivity and water system hydraulic connectivity to construct an evaluation system of water system connectivity.The final evaluation results of each scheme are compared with the evaluation criteria of water system connectivity,and the connectivity effect of each scheme is obtained.The connectivity of the first scheme is extremely poor,the connectivity of the second scheme is poor,and the connectivity of the third scheme is good.Therefore,the third scheme is the recommended scheme.