Keywords

1 Introduction

The water level difference is large between the upstream and downstream of navigation-power junction in the mountainous river. And the terrain on both banks is also complex. Usually the ship lock has the characteristics of high water head and large variation of navigable water level in mountainous area. The water-saving ship lock can not only save the water consumption of the ship lock, but also reduce the working head of each stage, which is conducive to solving the hydraulic problems of the high head ship lock. Therefore, it has been applied to several ship locks in China (Liu and Xuan 2019; Zhu and Xuan 2019). Baise ship lock in Guangxi is a typical case that adopts this water-saving scheme.

Baise water control project in Guangxi is located in the upper reaches of Youjiang River. It is a junction that focuses on flood control and has comprehensive utilization functions such as power generation, irrigation, navigation and water supply. The navigation buildings are arranged separately from the main buildings of the dam. They are located in Nalu ditch on the left bank of the main dam of the hydro project, including ship lock, intermediate channel and ship lift from upstream to downstream. The total length of the navigation route is about 4384 m. The total maximum navigation head of Baise hydro project is 113.6 m and the maximum design head of the ship lock is 25.0 m.

The effective dimension of Baise ship lock is 130 m × 12 m × 4.7 m (length × width × threshold depth). The designed ship types are 2 × 500t fleet and 1000t single ship. The upstream and downstream characteristic water levels of the lock during water saving operation are as follows: (1) The water level of upstream reservoir is 228.0 m to 214.0 m with the variation of 14.0 m. (2) The water level of downstream intermediate channel is 203.2 m to 203.0 m with the variation of 0.2 m.

2 Layout of the Water Saving Pools and Water Level Calculation

2.1 Construction Scheme of the Water Saving Pools

In combination with the project layout conditions, ship lock scale, operating head and navigation capacity requirements, it is determined that Baise ship lock is equipped with two-stage water saving pools through calculations and analyses. The topographic features of Baise ship lock site are low in the middle and high on both banks. Therefore, the water saving pools adopt decentralized layout scheme. And the high and low pools are respectively arranged on the left and right sides of the lock chamber. In order to make full use of the topographic conditions on both banks and reduce the amount of excavation and backfilling, the section shape of both pools is designed to be the new trapezoidal section form that is shown in Fig. 1.

Fig. 1.
figure 1

Typical cross section of the water saving pools and lock chamber

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2.2 Characteristic Water Level of the Pools

The classification of water level is very important for the operation of water saving ship lock. And many studies have been carried out by relevant scholars (Yang et al. 2021; Li and Xu 2020; He et al. 2020).

In this paper, the dynamic water valve closing mode is adopted in order to save water filling and emptying time. And there is a small amount of residual head between the pool and the chamber when the valves have been closed completely. Under the design condition with 0.15 m residual head, the characteristic water levels during water filling and emptying processes are calculated and analyzed for the trapezoidal section water saving pool scheme. The results are shown in Table 1 and Table 2. And Fig. 2 shows the initial and the end water levels of the water saving pools under three typical water level combinations. We can see that the characteristic water levels in the pools are obviously different because of the large variation range of the water level in upstream.

Table 1. Characteristic water levels during water filling from pools to chamber (unit: m)
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Table 2. Characteristic water levels during water emptying from chamber to pools (unit: m)
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Fig. 2.
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The initial and end water levels of the poos under three typical water level combinations

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3 Layout of Filling and Emptying System

3.1 Type of the Filling and Emptying System

Under the design maximum head of 25.0 m, when the ship lock adopts the water saving operation mode, the initial water head between the lock chamber and the pool is 10.09 m, and the initial water head between the lock chamber and the upstream or downstream approach channel is 10.24 m. The designed total water filling or emptying time should be no more than 16 min. Through the analysis of data indicators, it is found that the hydraulic index of the ship lock is high.

According to “Design Code for Filling and Emptying System of Shiplocks” (JTJ306-2001), it is calculated that the type discrimination coefficient of filling and emptying system is 1.87. So the distributed type should be selected. Furthermore, combined with the structural form of the chamber, lock bottom long-culvert filling and emptying system is adopted after comprehensive analyses.

3.2 Layout of the Filling and Emptying System

According to the research and calculation results, the section size of the culvert at the valves is 2.0 m wide and 3.0 m high. It can save water filling & emptying time and facilitate the operation management and maintenance of the ship lock that the culverts of the lock heads and the pools have the same control section in size.

The section size of the lock bottom culvert is 5.2 m wide and 3.0 m high. And 22 outlet branch holes are arranged on each side of the bottom culvert. The orifice size is 0.4 m wide and 0.9 m high. And the length of all the side branch holes is 1.2 m. In order to ensure the smooth flow and reduce the shape resistance of the branch holes, both ends of the inlet and outlet of the holes are rounded on three sides with a radius of 0.25 m. The center distance of adjacent holes is 4.0 m. In this way, the total length of chamber outlet section is 88.0 m, accounting for 67.7% of the effective length of lock chamber.

Two energy dissipation open ditches are arranged along the length direction of the lock chamber outside the outlet holes. The width of the open ditch is 2.2 m and the height of the retaining sill is 3.0 m. In order to guide the water flow to the middle of the chamber, the upper part of the open ditch is inclined to the center of the chamber according to the slope of 1:1.

Three inlet holes are arranged in each side culvert of the upper lock head. Each inlet hole is 3.0 m wide and 3.0 m high. The submerged water depth of the inlet holes is from 26.2 m to 12.2 m.

Considering that the downstream of the ship lock is connected with the intermediate channel and the ship lift, in order to meet the safety requirements of the ship lift, the water level fluctuation of the intermediate channel is limited. Therefore, for weakening the fluctuation in downstream approach channel and intermediate channel caused by the unsteady flow during lock emptying, an innovative layout of water outlet is proposed. Specifically, the outlet of the left culvert is arranged in the lower lock head and the right one is arranged in the downstream approach channel, with a spacing of 60.0 m. The outlet type is top branch holes of the energy dissipation chamber. Two stilling sills are set in the energy dissipation chamber to adjust the flow distribution and flow pattern in the holes and downstream approach channel. Moreover, the problem of uniform outflow will be also solved while emptying through single side culvert.

The outlet section at the top of the culverts of the pools is 4.0 m long and 2.0 m wide. And it is expanded around with a radius of 1.0 m to form a horn shaped outlet, which is connected with the bottom elevation of the water saving pool.

Table 3 shows the characteristic sectional areas of the filling and emptying system. The overall layout is shown in Fig. 3.

Table 3. The characteristic sectional areas of the filling and emptying system
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Fig. 3.
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Overall layout of the filling and emptying system

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4 Physical Model Test

4.1 Physical Model

According to the gravity similarity criterion, the overall physical model of the filling and emptying system of the ship lock with trapezoidal section pools is designed and established. The geometric scale between the model and the prototype is 1:20. The scope of the model includes the upstream and downstream reservoirs, lock chamber, the upper and lower lock heads, a full set of filling and emptying system, two water saving pools and some upstream and downstream approach channels, which is shown in Fig. 4.

Fig. 4.
figure 4

The overall physical model of filling and emptying system of ship lock with trapezoidal section pools

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Fig. 5.
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Flow pattern of downstream approach channel

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4.2 Hydraulic Characteristics

Through the physical model test, the hydraulic characteristic values of the ship lock under different operating conditions are obtained in Table 4. All hydraulic indexes meet the code requirements and the average filling and emptying time meets the design requirement. The discharge coefficient is 0.772 while lock filling from upstream, 0.701 emptying to downstream, 0.801 filling from pools and 0.722 emptying to pools. The results show that the hydraulic performance is superior. The theoretical water saving rate of the ship lock is 54.9% to 59.0% when the upstream water level changes between 214.0 m to 228.0 m.

The minimum pressure is 4.34 m water column during water filling process, which appears behind the water filling valve of the low pool. And it is 1.95 m during water emptying process, which appears behind the water emptying valve beside the lower lock head. So the culvert pressure conditions can meet the safety requirements of lock operation.

It is observed in the test that the innovative layout of the downstream outlet plays a certain role in weakening the water level fluctuation caused by watering emptying. The fluctuation is small in downstream approach channel and the outlet flow is evenly distributed along the transverse direction. The flow pattern of downstream approach channel is shown in Fig. 5.

Table 4. Hydraulic characteristic values under different operating conditions
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4.3 Berthing Conditions in Lock Chamber

The mooring force characteristics of 2 × 500t fleet and 1000t single ship in lock chamber are measured while water filling. Among them, the 1000t single ship berths at three typical positions: the upper, the middle and the lower part of the lock chamber. It can fully reflect the berthing conditions in this way.

Figure 6 shows the change process of mooring force of fleet and single ship in lock chamber under typical operating conditions. For 228 m–203 m water level combination condition, the maximum longitudinal mooring force of 2 × 500t fleet is 14.33 kN to 16.50 kN and the maximum transverse mooring force is 4.98 kN to 7.45 kN when the opening time of the pool valves is 1 min to 2 min. The maximum longitudinal and transverse mooring forces of the 1000t ship with a draft of 2.9 m are 11.19 kN to 21.23 kN and 4.56 kN to 10.60 kN respectively. The maximum mooring force of the ship is less than the allowable value of the code, and there is a certain surplus. The results indicate that the flow energy dissipation in lock chamber is good and the flow distribution is relatively uniform.

Fig. 6.
figure 6

The change process of mooring force of fleet and single ship in lock chamber

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4.4 Valve Operating Mode

According to the hydraulic characteristics, the culvert pressure conditions, the ship berthing conditions in lock chamber and the flow conditions in downstream approach channel, based on comprehensive analyses, the valve operating modes are recommended as follows: (1) The opening time of valves for water saving pools is 2.0 min, the remaining head is 1.5 m when they begin to close, and the closing time is 1.0 min; (2) The opening time of valves at the upper lock head is 2 min, and it is 3 min intermittently at the lower lock head. See Fig. 7 for details.

Fig. 7.
figure 7

Recommended valve operating modes

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5 Conclusions

In view of the characteristics of large water level drop, complex topography on both banks, high lock head and large variation of navigable water level of navigation-power junction in mountainous rivers, a two-stage new trapezoidal section water saving pool scheme of ship lock is studied and proposed. It can make full use of mountainous terrain conditions and reduce excavation and backfilling. On this basis, the water level classification of the ship lock is calculated, and the type and specific layout of filling and emptying system are studied and determined. The innovative scheme of decentralized layout of downstream outlets can meet the requirements of downstream intermediate channel flow conditions.

Through the physical model test, the hydraulic characteristics, culvert pressure characteristics, ship berthing conditions and key hydraulic indexes of the water saving ship lock are studied, and the operation modes of the valves are recommended.

The research shows that the hydraulic performance of the filling and emptying system is superior, and the hydraulic indexes and flow conditions under the recommended valve opening mode meet the requirements of the safe operation of the ship lock. The scheme of trapezoidal section water saving pools proposed in the study is reasonable and feasible in hydraulics. Within the range of design water level variation, the theoretical water saving rate of the ship lock is 54.9%–59.0%.