A system for treating river sludge suitable for land with limited space
By carrying out solid-liquid separation and wetland treatment of muddy water in the river channel, the problem of river silt treatment under the condition of land scarcity has been solved, and resource recycling and ecological balance have been achieved.
Patent Information
- Application Number
- CN202521387503.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-03
- Publication Date
- 2026-08-25
- Estimated Expiration
- 2035-07-03
AI Technical Summary
Given the scarcity of land around urban waterways, traditional methods for treating river silt are difficult to implement. Furthermore, dried mud cakes are not solid waste but a resource, requiring effective means of resource utilization.
The slurry water is separated into mud cake and leachate using a pressure filtration process. The mud cake is backfilled into the shallow wetlands inside the river channel for resource recycling, and the leachate is purified and discharged after being treated by a combination of anaerobic-aerobic-anaerobic wetlands.
It has achieved efficient disposal and resource utilization of riverbed sediment, reduced carbon emissions, maintained regional ecological balance, and avoided the occupation of public land.
Smart Images
Figure CN224677900U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of ecological water treatment technology, and in particular to a river silt treatment system suitable for areas with limited land. Background Technology
[0002] The most common method for cleaning riverbed sediment is the "drain-flushing-drying" process: first, the river water is drained, then the sediment is flushed with a high-pressure water gun, and finally, the slurry is pumped out using a sludge pump and piled up in nearby open areas to dry. Disposing of the resulting mud cakes as solid waste involves complex approval processes and is costly; therefore, resource recycling is a more economical approach.
[0003] However, in cities, the areas surrounding river channels are mostly built-up areas or roads, making it difficult to find enough open space for silt drying. This makes the traditional "draining-flushing-drying" treatment model difficult to implement. Furthermore, the dried silt cake is not only not solid waste but also a resource, requiring effective resource utilization methods for local use. Therefore, in the process of riverbed silt removal, how to utilize the limited space around urban river channels to achieve both efficient disposal of riverbed silt and resource utilization requires the development of more land-saving and ecological measures. Summary of the Invention
[0004] To address the aforementioned problems, this application provides a river silt treatment system suitable for situations where land is scarce.
[0005] The system first flushes the riverbed sediment, and the slurry is then filtered to form mud cakes. These mud cakes are then backfilled into the shallow wetlands inside the river channel, making use of local materials. This is a resource recycling model that uses local materials and resources locally, which can reduce carbon emissions and maintain the regional ecological balance. During the filtration process, the leachate produced is purified by the treatment module and can be directly discharged into the river.
[0006] To achieve the above objectives, this application provides a river silt treatment system suitable for areas with limited land, comprising a first treatment module, a second treatment module, and a third treatment module, wherein the first treatment module is connected to the second treatment module and also to the third treatment module;
[0007] The first processing module is located inside the river channel;
[0008] The second processing module includes an inlet unit, a wetland unit, an outlet unit, and a control module. The inlet unit is connected to the first processing module. The inlet unit, wetland unit, and outlet unit are connected in sequence. The inlet unit and outlet unit are both signal-connected to the control module.
[0009] The third module is located on both sides inside the river channel and is used to purify rainwater.
[0010] More specifically, the first processing module includes a collection unit located at the tail end of the river channel and a processing unit for treating the mud and water within the collection unit, wherein the collection unit is enclosed; the processing unit separates the mud and water into mud cake and leachate.
[0011] More specifically, the wetland unit includes a first anaerobic wetland, an aerobic wetland, and a second anaerobic wetland arranged sequentially. The first anaerobic wetland is connected to the inlet unit, and the second anaerobic wetland is connected to the outlet unit. The inlet unit includes an inlet pump, an inlet manual valve, an inlet flow meter, and an inlet electric valve. The inlet pump draws leachate. The outlet unit includes an outlet manual valve, an outlet flow meter, and an outlet electric valve.
[0012] More specifically, the first anaerobic wetland includes a first shell and a first filter material disposed inside the first shell. A first inlet is provided at the bottom of the inlet side of the first shell, and a first outlet is provided at the top of the outlet side of the first shell.
[0013] More specifically, the aerobic wetland includes a second shell, a second filter media disposed within the shell, and an aeration structure disposed within the second filter media. A second inlet is disposed at the top of the water inlet side of the second shell, and a second outlet is disposed at the bottom of the water outlet side of the second shell. The second inlet is connected to the first outlet.
[0014] More specifically, the second filter media is configured as a first aeration zone, a second aeration zone, and a non-aeration zone. The first aeration zone is close to the inlet side, the non-aeration zone is close to the outlet side, and the second aeration zone is located between the first aeration zone and the non-aeration zone. There are two layers of aeration in the first aeration zone, one layer of aeration in the second aeration zone, and no aeration in the non-aeration zone.
[0015] More specifically, the second anaerobic wetland includes a third shell, a third filter media disposed within the third shell, and a baffle assembly disposed within the third filter media. A third inlet is provided at the bottom of the inlet side of the third shell, and a third outlet is provided at the top of the outlet side of the third shell. The third inlet is connected to the second outlet, and the third outlet is connected to the outlet unit.
[0016] More specifically, the baffle assembly includes a first baffle plate group and a second baffle plate group. The end of the first baffle plate group away from the second baffle plate group is flush with the bottom of the third filter material, and the end of the second baffle plate group away from the first baffle plate group is flush with the top of the third filter material. The first baffle plate group and the second baffle plate group are arranged alternately.
[0017] More specifically, the first baffle group includes a plurality of uniformly arranged first baffles, and the second baffle group also includes a plurality of uniformly arranged second baffles. A second baffle is arranged between every two adjacent first baffles, and a first baffle is arranged between every two adjacent second baffles.
[0018] More specifically, the third processing module is set as a shallow wetland, and the mud cake is transported to the shallow wetland.
[0019] The beneficial effects of a river sludge treatment system suitable for land-constrained river channels are as follows: During process design, riverbed sludge is collected within a cofferdam area inside the river channel, with the cofferdam's bottom angled. This avoids occupying external river resources and allows for rapid collection and extraction of the sludge. In the second treatment module's process design, a combination of a first anaerobic wetland, an aerobic wetland, and a second anaerobic wetland effectively removes nitrogen from the leachate. The aerobic wetland effectively removes carbon, while phosphorus is removed through the adsorption of the ecological filter media. The piping design of the second treatment module incorporates combinations of low-inlet-high-outlet, high-inlet-low-outlet, and low-inlet-high-outlet configurations, maximizing the production efficiency of the anaerobic-aerobic-anaerobic process. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the overall structure of this utility model;
[0021] Figure 2 This is a schematic diagram of the structure of the second processing module of this utility model;
[0022] Figure 3 This is a schematic diagram of the first anaerobic wetland structure of this utility model;
[0023] Figure 4 This is a schematic diagram of the aerobic wetland structure of this utility model;
[0024] Figure 5 This is a schematic diagram of the second anaerobic wetland structure of this utility model;
[0025] Figure 6 This is a schematic diagram of the third processing module structure of this utility model;
[0026] Figure 7 This is a schematic diagram of the river channel structure of this utility model;
[0027] In the diagram: 1. River channel; 2. First treatment module; 3. Second treatment module; 30. Inlet pump; 31. Inlet manual valve; 32. Inlet flow meter; 33. Inlet electric valve; 34. Outlet manual valve; 35. Outlet flow meter; 36. Outlet electric valve; 37. First anaerobic wetland; 371. First shell; 372. First filter media; 373. First inlet pipe; 374. First outlet pipe; 38. Aerobic wetland; 381 382. Second shell; 383. Second filter media; 384. Aeration structure; 385. Second outlet pipe; 39. Second anaerobic wetland; 396. Third shell; 397. Third filter media; 398. Third outlet pipe; 399. First baffle plate; 390. Second baffle plate; 4. Third treatment module; 41. Fixed pile; 42. Mud cake; 43. Coarse sand and gravel; 44. Wetland plants; 5. Rainwater outlet; 6. Riverbank; →, Water flow direction; Direction of mud cake conveying. Detailed Implementation
[0028] A river silt treatment system suitable for land-constrained areas, such as Figures 1-7 As shown, it includes a first processing module 2, a second processing module 3 and a third processing module 4. The first processing module 2 is connected to the second processing module 3 and the third processing module 4 are connected to each other.
[0029] The first processing module 2 includes a collection unit located at the tail of the river channel 1. The water flow direction of the river channel 1 is towards the tail of the river channel 1, that is, all the water in the river channel 1 will eventually flow to the collection unit at the tail of the river channel 1. In order to treat the bottom sediment of the river channel 1, the bottom sediment of the river channel 1 is first flushed. Therefore, the flushing direction in the river channel 1 is also towards the tail of the river channel 1. The mud and water generated by flushing flows towards the collection area at the tail of the river channel 1 and is stored in the collection unit.
[0030] The collection unit can be any structure capable of both water intake and storage. In this design, the collection unit is a cofferdam, used to contain the muddy water. The sides of the cofferdam are sealed to prevent the muddy water from flowing downstream of river channel 1. A water pump is installed inside the cofferdam to extract the muddy water. For better collection and discharge, the bottom of the cofferdam area is sloped, gradually decreasing in height with the direction of water flow. Furthermore, the bottom of the cofferdam area is set at an angle following the direction of river channel 1, with the angle selectable within the range of 15°-30°.
[0031] The mud and water stored in the collection area need to be dried, so a treatment unit is set up in the collection area to treat the mud and water in the cofferdam. The treatment unit performs solid-liquid separation on the mud and water in the collection area. The mud cake 42 separated from the solid and liquid is transferred to the third treatment module 4, and the leachate separated from the solid and liquid is transported to the second treatment module 3. Furthermore, a mud cake collection area and a leachate collection area are set up. The mud cake 42 separated by the treatment unit can be placed in the mud cake collection area or directly transported to the third treatment module 4. The leachate can be stored in the leachate treatment area. The treatment unit can not only quickly treat the silt in the river, but also avoid occupying public land and avoid the problem of insufficient public land for drying silt. The treatment unit can be set as any structure that can operate on the mud and water. In this solution, the treatment unit is set as a filter press for solid-liquid separation of mud and water. The filter press can adjust the water volume and extraction speed of the leachate.
[0032] The filter press separates the mud slurry into dry mud cake 42 and leachate. The dry mud cake 42 can be directly reused, while the leachate is transported to the second processing module 3 for purification.
[0033] The second processing module 3 includes an inlet unit, a wetland unit, an outlet unit, and a control module. The control module automatically controls the inlet and outlet water flow. The inlet unit delivers the leachate to the wetland unit, and the outlet unit sends the treated purified water out of the wetland unit. Several wetland units can be configured, connected in parallel. Each wetland unit includes a first anaerobic wetland 37, an aerobic wetland 38, and a second anaerobic wetland 39 arranged sequentially. The inlet unit includes an inlet water pump 30, an inlet manual valve 31, an inlet flow meter 32, and an inlet electric valve 33 connected together. The outlet unit includes an outlet manual valve 34, an outlet flow meter 35, and an outlet electric valve 36 connected together.
[0034] The inlet unit is connected to the leachate collection area. The leachate in the collection area enters the wetland unit for purification through the inlet unit. The outlet of the leachate collection area is higher than the inlet of the wetland unit, allowing the leachate to be transported to the wetland unit without power. When the leachate volume is sufficient, it is directly transported from the leachate collection area to the wetland unit without power. However, when the leachate volume in the collection area is low, the leachate is transported to the wetland unit by the inlet pump 30 located in the leachate treatment area. The control unit controls the inlet pump 30 to extract the leachate from the leachate treatment area. The control module controls the inlet electric valve 33 to open, and the leachate enters the first anaerobic wetland 37 for purification. The inlet flow meter 32 detects the inlet flow rate and transmits the signal to the control module. The control module records the inlet flow rate and adjusts the pumping speed of the inlet pump 30 or the opening of the inlet electric valve 33 according to the flow rate of the inlet flow meter 32 to control the inlet volume. The manual inlet valve 31 is normally open. It should only be manually adjusted to the closed state when the system is under maintenance.
[0035] When multiple wetland units are set up, each wetland unit is equipped with an electric inlet valve 33 at its inlet end, but only one set of inlet pump 30, manual inlet valve 31 and inlet flow meter 32 can be set up.
[0036] The first anaerobic wetland 37 needs to maintain an anaerobic state. The first anaerobic wetland 37 is designed to operate with full water during operation, and the first anaerobic wetland 37 is configured with a bottom inlet and top outlet structure. The first anaerobic wetland 37 includes a first shell 371 and a first filter media 372 disposed within the first shell 371. A first inlet is disposed at the bottom of the inlet side of the first shell 371, and a first inlet pipe 373 is disposed on the first inlet. The inlet unit is disposed on the first inlet pipe 373 to control whether leachate enters and the inlet flow rate. A first outlet is disposed at the top of the outlet side of the first shell 371, and a first outlet pipe 374 is disposed on the first outlet. The water purified in the first anaerobic wetland 37 enters the aerobic wetland 38 through the first outlet pipe 374.
[0037] In actual production, the leachate produced by the filter press has a low oxygen content. Taking advantage of this characteristic, the first wetland in the wetland unit is designated as the first anaerobic wetland 37, primarily for nitrogen and phosphorus removal. During leachate transport, contact with air is minimized to maintain a low oxygen content. Therefore, in the treatment process, the leachate first enters the anaerobic environment, preferentially passing through which some NO2- and NO3- are converted to N2, thus removing some NO2- and NO3-. In the structural design of the treatment process, a bottom-inlet and top-outlet design is used to minimize leachate contact with air during transport and reaction. Phosphorus is mainly removed through adsorption by the ecological filter media.
[0038] The aerobic wetland 38 is a vertical flow wetland, with water entering from the top and exiting from the bottom. The aerobic wetland 38 includes a second shell 381, a second filter media 382 disposed within the second shell 381, and an aeration structure 383 disposed within the second filter media 382. The water level in the aerobic wetland 38 is lower than the height of the second filter media 382. A second inlet is located at the top of the water inlet side of the second shell 381, and a first outlet pipe 374 is connected to the second inlet. A second outlet is located at the bottom of the water outlet side of the second shell 381, and a second outlet pipe 384 is installed on the second outlet. The filtered water from the aerobic wetland 38 is transported to the second anaerobic wetland 39 through the second outlet pipe 384. The aerobic wetland 38 can effectively remove carbon, while phosphorus can be removed through the adsorption of the ecological filter media.
[0039] In actual production, the aerobic wetland 38 requires a large amount of oxygen, while the oxygen content of the water coming from the first anaerobic wetland 37 is low. Therefore, the first anaerobic wetland 37 adopts an upward effluent method, which increases the chance of the effluent from the first anaerobic wetland 37 coming into contact with air. Furthermore, an aeration structure 383 needs to be set up to oxygenate the wetland and the incoming water. At the same time, after the incoming water enters the aerobic wetland 38, a large amount of oxygen needs to be replenished quickly. Therefore, a trapezoidal aeration system is set up in the aerobic wetland 38, with the aeration rate increasing closer to the incoming water end. Furthermore, the aerobic wetland 38 is vertically divided into three areas along the horizontal direction, which are sequentially set as a first aeration zone, a second aeration zone, and a non-aeration zone. The first aeration zone is close to the inlet side, the non-aeration zone is close to the outlet side, and the second aeration zone is set between the first aeration zone and the non-aeration zone. Two layers of aeration are set in the first aeration zone, one layer of aeration is set in the second aeration zone, and no aeration is set in the non-aeration zone.
[0040] The aeration structure 383 is configured with several aeration discs. Two aeration discs are located in the first aeration zone, arranged vertically to allow for rapid oxygen replenishment of the incoming water from the first anaerobic wetland 37. One aeration disc is located at the bottom of the second aeration zone. Since less oxygen is needed by the time the incoming water reaches the second aeration zone, only one aeration disc is used. However, the aeration disc in the second aeration zone can be the same as the one located below in the first aeration zone. This larger disc covers both aeration zones. No aeration discs are used in non-aeration zones because the next module after the aerobic wetland 38 is an anaerobic wetland; therefore, aeration is stopped before the water enters the anaerobic wetland to allow it to acclimatize to the anaerobic environment. Each of the aeration discs can be individually connected to an air inlet pipe, or they can be connected to a single air inlet pipe for unified air intake.
[0041] The second anaerobic wetland 39 is also an anaerobic wetland, operating fully filled with water, with water entering from the bottom and exiting from the top. Since the oxygen content needs to be gradually reduced in this section, the size of the second anaerobic wetland 39 is larger than that of the first anaerobic wetland 37 and also larger than that of the aerobic wetland 38; furthermore, the size of the second anaerobic wetland 39 is equal to or greater than the sum of the sizes of the first anaerobic wetland 37 and the aerobic wetland 38. The second anaerobic wetland 39 includes a third shell 391, a third filter media 392 disposed within the third shell 391, and a baffle assembly disposed within the third filter media 392. A third inlet is provided at the bottom of the inlet side of the third shell 391, and the second outlet pipe 384 is connected to the third inlet. A third outlet is provided at the top of the outlet side of the third shell 391, and a third outlet pipe 393 is disposed on the third outlet. The outlet unit is disposed on the third outlet pipe 393.
[0042] The third filter media 392 comprises filter media, rice husks, and industrial sugar to supplement carbon (C) and help convert NO2- or NO3- in the leachate into N2 as much as possible, while effectively removing organic matter contained in the leachate itself; the proportion of industrial sugar is less than that of filter media and rice husks.
[0043] To ensure an extended flow path for the incoming water within the second anaerobic wetland 39, thereby improving the removal efficiency of NO2- or NO3- in the aerobic wetland 38, the second anaerobic wetland 39 is configured as a baffle system. The baffle assembly includes a first baffle plate group and a second baffle plate group. The first baffle plate group includes several uniformly arranged first baffle plates 394, and the second baffle plate group also includes several uniformly arranged second baffle plates 395. The end of the first baffle plate group furthest from the second baffle plate group is flush with the bottom of the third filter media 392, and the end of the second baffle plate group furthest from the first baffle plate group is flush with the top of the third filter media 392. A second baffle plate 395 is positioned between every two adjacent first baffle plates 394, and a first baffle plate 394 is positioned between every adjacent second baffle plates 395, arranged in an alternating pattern. This allows the leachate to form a baffle flow within the second anaerobic wetland 39, removing nitrogen and consuming oxygen.
[0044] If the purified effluent filtered from the second anaerobic wetland 39 meets the discharge requirements, it is directly discharged into the external river for use. If it does not meet the requirements, it is re-entered into the wetland unit for treatment until it meets the requirements.
[0045] Under normal circumstances, one set of wetland units is sufficient. If there is a lot of mud and water in the river channel 1, two or more sets of wetland units can be set up for treatment.
[0046] The water outlet unit is installed on the third water outlet pipe 393, and the electric water outlet valve 36 is controlled by a control module. Data from the inlet flow meter 32 and the outlet flow meter 35 are transmitted back to the control module, which adjusts the water outlet speed and detects any malfunctions in the wetland unit based on the data from the outlet flow meter 35. The manual water outlet valve 34 is not used under normal circumstances; it is only opened or closed manually during system maintenance.
[0047] The second processing module 3 is movable.
[0048] The third processing module 4 is set as a shallow wetland. The silt in the river channel 1 is dried into mud cakes 42 and then returned to the river channel 1 for reuse. At this time, shallow wetlands are set on both sides of the river channel 1. In order to avoid occupying the position of the riverbank 6, the shallow wetland is set in the river channel 1 and extends along the direction of the river channel 1.
[0049] The shallow wetland includes fixed piles 41 installed in the river channel 1. Several fixed piles 41 are arranged sequentially in the river channel 1, forming a wetland space between the fixed piles 41 and the edge of the river channel 1. At the bottom of the wetland space, dry mud cakes 42, which are filtered out by a filter press, are laid. Since the mud cakes 42 are the original silt in the river channel 1, they can be used directly. Coarse sand and gravel 43 are laid on top of the mud cakes 42, and wetland plants 44 are planted on the coarse sand and gravel 43. Under normal circumstances, the height of the shallow wetland is higher than the normal water level of the river in the river channel 1. However, during the flood season, the water level in the river channel 1 will be level with the height of the shallow wetland. The mud cakes 42 are not submerged in the river water all year round. The shallow wetland provides purification for the water entering the river.
[0050] A number of rainwater outlets 5 are provided on the riverbank 6. The rainwater outlets 5 are evenly distributed along the riverbank line. The position of the riverbank 6 is higher than that of the shallow wetland. Therefore, the position of the rainwater outlets 5 is also higher than that of the shallow wetland. The water flowing out of the rainwater outlets 5 first enters the shallow wetland. The shallow wetland purifies the water flowing in from the rainwater outlets 5. The purified water finally flows into the river channel 1.
Claims
1. A river silt treatment system suitable for areas with limited land, characterized in that: It includes a first processing module (2), a second processing module (3) and a third processing module (4). The first processing module (2) is connected to the second processing module (3) and the first processing module (2) is also connected to the third processing module (4). The first processing module (2) is set in the river channel (1) and is used to collect and process the mud and water in the river channel (1); The second processing module (3) includes an inlet unit, a wetland unit, an outlet unit, and a control module. The inlet unit is connected to the first processing module (2). The inlet unit, the wetland unit, and the outlet unit are connected in sequence. The inlet unit and the outlet unit are both signal-connected to the control module. The third processing module (4) is located on both sides inside the river channel (1) and is used to purify rainwater.
2. The river silt treatment system according to claim 1, characterized in that: The first processing module (2) includes a collection unit located at the tail end of the river channel (1) and a processing unit for treating the mud and water in the collection unit. The collection unit is enclosed. The processing unit separates the mud and water into mud cake (42) and leachate.
3. The river silt treatment system suitable for land-constrained areas according to claim 2, characterized in that: The wetland unit includes a first anaerobic wetland (37), an aerobic wetland (38), and a second anaerobic wetland (39) arranged sequentially. The first anaerobic wetland (37) is connected to the influent unit, and the second anaerobic wetland (39) is connected to the effluent unit. The water inlet unit includes a water inlet pump (30), a manual water inlet valve (31), a water inlet flow meter (32), and a water inlet electric valve (33). The water inlet pump (30) draws leachate and delivers it to the first anaerobic wetland (37). The water outlet unit includes a manual water outlet valve (34), a water outlet flow meter (35), and a power water outlet valve (36).
4. The river silt treatment system suitable for land-constrained areas according to claim 3, characterized in that: The first anaerobic wetland (37) includes a first shell (371) and a first filter material (372) disposed in the first shell (371). A first inlet is provided at the bottom of the water inlet side of the first shell (371), and a first outlet is provided at the top of the water outlet side of the first shell (371).
5. The river silt treatment system according to claim 4, characterized in that: The aerobic wetland (38) includes a second shell (381), a second filter media (382) disposed in the shell, and an aeration structure (383) disposed in the second filter media (382). A second inlet is provided at the top of the water inlet side of the second shell (381), and a second outlet is provided at the bottom of the water outlet side of the second shell (381). The second inlet is connected to the first outlet.
6. The river silt treatment system according to claim 5, characterized in that: The second filter media (382) is configured as a first aeration zone, a second aeration zone and a non-aeration zone. The first aeration zone is close to the inlet side and the non-aeration zone is close to the outlet side. The second aeration zone is located between the first aeration zone and the non-aeration zone. Two layers of aeration are provided in the first aeration zone and one layer of aeration are provided in the second aeration zone.
7. The river silt treatment system according to claim 5, characterized in that: The second anaerobic wetland (39) includes a third shell (391), a third filter media (392) disposed in the third shell (391), and a baffle assembly disposed in the third filter media (392). A third water inlet is provided at the bottom of the water inlet side of the third shell (391), and a third water outlet is provided at the top of the water outlet side of the third shell (391). The third water inlet is connected to the second water outlet, and the third water outlet is connected to the water outlet unit.
8. The river silt treatment system according to claim 7, characterized in that: The baffle assembly includes a first baffle plate group and a second baffle plate group. The end of the first baffle plate group away from the second baffle plate group is flush with the bottom of the third filter material (392), and the end of the second baffle plate group away from the first baffle plate group is flush with the top of the third filter material (392). The first baffle plate group and the second baffle plate group are arranged alternately.
9. The river silt treatment system according to claim 8, characterized in that: The first baffle group includes a plurality of uniformly arranged first baffles (394), and the second baffle group also includes a plurality of uniformly arranged second baffles (395). A second baffle (395) is arranged between each pair of adjacent first baffles (394), and a first baffle (394) is arranged between each pair of adjacent second baffles (395).
10. The river silt treatment system according to claim 2, characterized in that: The third processing module (4) is set as a shallow wetland, and the mud cake (42) is transported to the shallow wetland.