Simulating a pumped pond – Fatal Error

[Andrew Brown]

Hello everyone,

so I’m attempting to model a small sediment/stormwater pond that will have a pond in it to remove water as it comes it (hooked up to a float switch to set it off). The pond is essentially a 2 m deep turkey’s nest. Essentially I have attempted to force RORB into roughly doing the calculations by adding in a reservoir with a set H-S and S-Q relationship. It is sometimes working, other times I’m getting Fatal errors where it appears RORB is struggling to interpolate.

How I spoofed pumping behavior is by setting the pump rate as the discharge value at 1.7 m depth (pond depth, 300 mm freeboard) and then subtracting 0.001 m3/s from that value until making the final jump to zero. Currently for this combination of S-Q and H-S it’s crashing for anything exceeding 0.293 m3/s.

S-Q and H-S is as follows:
1, .000, 22, Storage-discharge table (2 values x 22 lines)
0.000, 0.000,
330.146, 0.284,
668.751, 0.285,
1015.888, 0.286,
1371.633, 0.287,
1736.059, 0.288,
2109.240, 0.289,
2491.252, 0.290,
2882.169, 0.291,
3282.064, 0.292,
3691.013, 0.293,
4109.090, 0.294,
4536.368, 0.295,
4972.923, 0.296,
5418.829, 0.297,
5874.160, 0.298,
6338.991, 0.299,
6813.396, 0.300,
7297.449, 0.301,
7791.225, 0.302,
8294.798, 0.303,
50000.000, 0.304,
-99
C Elevation-storage relationship
1, 22, Elevation-storage table (2 values x 22 lines)
0.000, 0.000,
0.100, 330.150,
0.200, 668.750,
0.300, 1015.890,
0.400, 1371.630,
0.500, 1736.060,
0.600, 2109.240,
0.700, 2491.250,
0.800, 2882.170,
0.900, 3282.060,
1.000, 3691.010,
1.100, 4109.090,
1.200, 4536.370,
1.300, 4972.920,
1.400, 5418.830,
1.500, 5874.160,
1.600, 6338.990,
1.700, 6813.400,
1.800, 7297.450,
1.900, 7791.230,
2.000, 8294.800,
10.000, 50000.000,

Any ideas why it’s crashing and not allowing the reservoir to fill above 1 m of depth?

kind regards,

Andrew

[Benson Liu]

Hi Andrew,

It is a little hard to tell exactly why RORB is crashing, but I have encountered something similar to this before where RORB has trouble interpolating when the discharge is barely changing with increases in storage.

While this is a little clunky, what you can do is fudge the storage discharge relationship such that no water is exiting the storage at all and then insert an outflow/diversion upstream of the storage. With the diversion you specify a relationship between the water coming in and the water being “diverted”. This diversion you can set to 0.3 m³/s to simulate the pump. You can then set an inflow downstream of the storage so the pumped/diverted water then comes in downstream of storage. I believe doing this should get around the interpolation error. Let me know if you are still having problems.

Kind regards,

Benson

[Andrew Brown]

Hi Benson,

I somehow got around it by using a discharge curve that looked like this:
Depth Volume Discharge
0.00 0.000 0.000
0.10 132.644 0.099
1.70 3022.531 0.100
2.00 3731.545 0.101
12.00 50000.000 0.700

Which roughly goes with a pump switching on from a float switch. Over 2 m of depth the pond has overflowed o that’s why it jumps up on the last step. That worked for the majority of my runs though I just had one fail with this discharge curve when the flows exceeded 0.4 m3/s.

1, .000, 5, Storage-discharge table (2 values x 5 lines)
0.000, 0.000,
132.640, 0.399,
3022.530, 0.400,
3731.540, 0.401,
50000.000, 0.700,

I tried playing with the discharge numbers and eventually got it to run successfully after playing around with the values slightly to the following:
1, .000, 5, Storage-discharge table (2 values x 5 lines)
0.000, 0.000,
132.640, 0.398,
3022.530, 0.400,
3731.540, 0.405,
50000.000, 1.000,

I had considered using the inflow/outflow function but with this situation the pond is a contact water pond that will pump water to a disused open mine pit. As such the attenuation within the pond is very significant when it comes to the sizing of the pump. So bypassing the storage will likely not be suitable in this case.

kind regards,

Andrew

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