The simulation in this article was performed in Environment and Climate changes Research Institute (ECRI) by using the CORMIX3 (Version 11. 0 GTD) modeling program. The required data for outfall effluent characteristics and geometry, ambient flow and geometry as well as water quality data at the beginning of the canal and at the proposed discharge location was collected during a short-term field study conducted by Water Management Research Institute (WMRI) in September 2020. Average wind speed was collected from the nearest available metrological station in 23-9-2020 which is available in website;
https://en.tutiempo.net/climate/09-2020/ws-623660.html.
Theoretical Background for Model
One of the mathematical models that were developed for submerged round buoyant jets is length-scale model. In this model, surface discharge flows can be divided up into different regimes each dominated by particular flow properties such as the initial momentum, the buoyancy flux, or the ambient cross flow (6).
CORMIX is one the length scale models, which is a rule-based mixing model for surface water that predicts mixing and dilution of several types of effluent into various water bodies (7). CORMIX contains about 80 generic flow classifications for submerged single port, multiport, and surface discharge sources (8).
CORMIX simulates the hydrodynamics of both near-field and far-field mixing zones. The mixing in the near-field is highly dependent on the discharge conditions, whereas it is dependent solely on the ambient conditions in the far-field (6).
Model Description
CORMIX model deduces which hydrodynamic method is best fit for each simulation by referring to what is known as a rule based expert system. CORMIX has four core hydrodynamic mixing zone simulation models to simulate diverse discharge situations. These hydrodynamic models are CORMIX1, CORMIX2, CORMIX3, and DHYDRO for single port, multiport, surface, and dense/sediment discharges, respectively. The model allows working with five different types of pollutants including conservative pollutants, where the parameter does not undergo any decay/growth process and non-conservative pollutants, where the parameter suffers decay of the first order decay or growth process, as well as for heated discharge, brine discharge and sediment discharge. In CORMIX, the interaction between the ambient conditions of the receiving body and the discharge characteristics govern the mixing behavior of any wastewater discharge. Regarding the calculation process, CORMIX assumes the receiving water body as rectangular cross-section (6) and (7). In addition, the discharge configurations in CORMIX3 are three types; flush, protruding, and coflowing.
Regarding the assistant tools, the CORMIX package has some post processing tools, including CorVue, which is an interactive 3-D visualization tool that displays mixing zone processes and the behavior of wastewater plumes. In addition, CORMIX has preprocessor tools for computation of data input including CorSpy, which is a tool for interactive 3D visualize, display and specification of outfall properties, including ambient (7).
Study Area
The investigated system (Figure 1) consists of (Mit Yazid canal) that represent the ambient water body and the outlet of a drain (Mehalet Rough pumping station) that dump the drainage water of Waslet Mehalet Rough drain into Mit Yazid canal (km 3.0 on the canal).
Mit Yazid canal is one of the main canals in the Middle Delta (Figure 2). It off-takes from Bahr Shibin canal (km 96.50). The canal is 63.0 km long and it is located within the administrative boundaries of Gharbiya and Kafr El Sheikh Governorates (71% of the total area is within Kafr El Sheikh). Mit Yazid main canal is feeding 60 branch canals, and it generally flows in a northern to north-western direction and ends immediately south of El Burullus Lake (9). One main characteristics of Mit Yazid canal is the spreading on municipal water stations along the canal, which requires maintaining the water quality in the canal within the standard values according to the Egyptian law for the Ministry of Water Resources and Irrigation, to protect the Nile River and Waterways from Pollution (law 48/1982- article No. 49) (10). The closest municipal station to Mehalet Rough pumping station is at km 6.2 on Mit Yazid canal.
Mehalet Rough pumping station is the outlet of Waslet Mehalet Rough drain that collected the drainage water from five drains; namely Tukh drain, El-Santah drain, Bilay drain, Samatai El-Ala drain and Mehalet Rough drain. Average effluent from the pumping station to Mit Yazid canal is 300,000 m3/day (9). The station has four electric pumping units with an average capacity of 2.50 m3/sec (Total capacity of the station is 10.0 m3/sec). Only two units are operated together with a total discharge of 5.0 m3/sec. The flow regime for the pump station outfall into Mit Yazid canal is surface discharge. According to CORMIX classification it is considered CORMIX3 configuration.
Collected Data
Collected data included the geometry, the configuration and the flow characteristics of the ambient and the pumping station.
The ambient data
Figure (3) presents the cross section of Mit Yazid canal at km 3.0 (close to the outlet of Mehalet Rough pumping station).
From the figure, the bed level is around 2.80 m and the bed width is around 40.0 m. Average water level in September 2020 (simulation time) was 5.18 m, and therefore, the water depth for the ambient was 2.38 m. The flow rate in the canal during the studied period was 70.8 m3/s. Based on the studied in WMRI, Manning coefficient for Mit Yazid canal is 0.03.
Pumping station data
Mehalet Rough pumping station is located at the left bank of Mit Yazid canal. The configuration structure for pumping station is flush with the bank. The horizontal angle of discharge (sigma angle-σ) with the canal is 53 degree (figure 4).
Water quality data
The Egyptian water quality standard provides conditions for fresh water and for the agriculture drainage water before discharging into fresh water.
For the fresh water (Mit Yazid canal), BOD should not exceed 6.0 ppm and TDS should not exceed 500 ppm. Based on field measurements, BOD and TDS values in Mit Yazid canal upstream the study were 2 ppm and 265 ppm respectively (table 1).
For the agriculture drainage water (Mehalet Rough) BOD should not exceed 10.0 ppm and TDS should not exceed 500 ppm (law 48/1982- article No. 64) (10). Based on field measurements, BOD and TDS values in Mehalet Rough drain was 19 ppm and 589 respectively (table 1).
The discharge channel geometry for CORMIX3
Figure (5) presents the specifications required for CORMIX3. These specifications include location of the nearest bank, ambient depth near the surface discharge channel entry (HD), discharge channel width (B0) of the rectangular channel, discharge channel depth (H0), actual receiving water depth at the channel entry (HD0), bottom slope (SLOPE) in the receiving water body in the vicinity of the discharge channel, and horizontal angle of discharge (SIGMA) is the angle of the surface shoreline discharge channel with respect to the downstream bank.
Table (1)
Discharge and water quality values for the ambient and the outfall
Ambient/outfall
|
Flow rate (m3/s)
|
BOD (ppm)
|
TDS (ppm)
|
BOD Excess above the ambient
|
Excess TDS above the ambient
|
Ambient background
|
outfall
|
Ambient background
|
outfall
|
Mit Yazid canal
|
70.8
|
2
|
----
|
265
|
----
|
------
|
------
|
Pump Station
|
5
|
------
|
19
|
------
|
598
|
17
|
333
|
In the immediate area of the discharge, the actual depth of the receiving water, HD, may be somewhat different from the average ambient depth, Ha. The bottom of the channel may be sloping away from the discharge bank at an angle θ, beginning with the depth immediately in front of the discharge channel, HDO.
Input Data
There are three types of input data that are required for using the CORMIX model; Environmental ambient data, effluent data, and disposal type information as subaquatic emissary data. The collected data in this article for discharge type (CORMIX3 model) was presented in table (2).
Table (2)
Environmental, Effluent and Subaquatic emissary data
Parameter
|
Value
|
Environmental data
|
Cross-section
|
bounded
|
Flow rate - (m3/s)
|
70.8
|
Average depth (HA) (m)
|
2.38
|
Ambient depth near the surface discharge channel entry (HD) - (m)
|
3.1
|
Actual receiving water depth at the channel entry (HD0) - (m)
|
0.75
|
Bottom slope – (degree)
|
37.89
|
Manning coefficient
|
0.03
|
Distance between ambient banks (BS-width) - (m)
|
55
|
Temperature – (°C)
|
29.8
|
Average wind speed (m/sec(
|
4.94
|
Effluent data
|
Flow rate - (m3/s)
|
5
|
Temperature – (°C)
|
29.8
|
Subaquatic emissary data
|
Discharge channel depth (H0) - (m)
|
0.75
|
Location of the nearest bank (i.e. left or right)
|
left
|
Discharge channel width (B0) - (m)
|
10
|
Horizontal angle of discharge (sigma angle) – (degree)
|
53
|