Supplemental Tables.
Table S1. WASP hydraulic input parameters for each simulated stream segment under estimated
current burial conditions.
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
1
1
1
1
1
6
6
6
6
6
7
7
7
7
7
7
7
7
8
8
8
8
9
9
9
9
9
9
9
16
16
16
16
16
17
17
17
17
17
17
17
17
21
21
21
21
21
21
21
21
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Surface Area
Volume
Width
Depth
(m2)
881
881
881
881
881
1119
1119
1119
1119
1119
1153
1153
1153
1153
1153
1153
1153
1153
427
427
427
427
1188
1188
1188
1188
1188
1188
1188
1550
1550
1550
1550
1550
1577
1577
1577
1577
1577
1577
1577
1577
1668
1668
1668
1668
1668
1668
1668
1668
(m3)
598
598
598
598
598
910
910
910
910
910
958
958
958
958
958
958
958
958
168
168
168
168
1010
1010
1010
1010
1010
1010
1010
1613
1613
1613
1613
1613
1662
1662
1662
1662
1662
1662
1662
1662
1834
1834
1834
1834
1834
1834
1834
1834
(m)
(m)
4.41
4.41
4.41
4.41
4.41
5.60
5.60
5.60
5.60
5.60
5.76
5.76
5.76
5.76
5.76
5.76
5.76
5.76
2.14
2.14
2.14
2.14
5.94
5.94
5.94
5.94
5.94
5.94
5.94
7.75
7.75
7.75
7.75
7.75
7.88
7.88
7.88
7.88
7.88
7.88
7.88
7.88
8.34
8.34
8.34
8.34
8.34
8.34
8.34
8.34
Slope
0.68
0.68
0.68
0.68
0.68
0.81
0.81
0.81
0.81
0.81
0.83
0.83
0.83
0.83
0.83
0.83
0.83
0.83
0.39
0.39
0.39
0.39
0.85
0.85
0.85
0.85
0.85
0.85
0.85
1.04
1.04
1.04
1.04
1.04
1.05
1.05
1.05
1.05
1.05
1.05
1.05
1.05
1.10
1.10
1.10
1.10
1.10
1.10
1.10
1.10
0.006
0.007
0.003
0.003
0.006
0.004
0.006
0.007
0.003
0.003
0.002
0.000
0.000
0.000
0.000
0.000
0.000
0.027
0.011
0.015
0.006
0.006
0.007
0.005
0.006
0.002
0.003
0.006
0.000
0.000
0.000
0.000
0.004
0.003
0.006
0.003
0.004
0.017
0.001
0.001
0.004
0.004
0.003
0.004
0.005
0.006
0.002
0.001
0.000
0.000
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
22
22
22
22
22
22
22
23
23
24
24
24
25
25
25
25
25
25
28
28
28
28
28
28
28
28
28
28
29
29
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
31
32
32
Open
Open
Open
Open
Open
Buried
Buried
Buried
Buried
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
(m 2 )
(m 3 )
1688
1688
1688
1688
1688
1688
1688
1715
1715
1737
1737
1737
1769
1769
1769
1769
1769
1769
1910
1910
1910
1910
1910
1910
1910
1910
1910
1910
1918
1918
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1968
1985
1985
1873
1873
1873
1873
1873
1873
1873
1926
1926
1969
1969
1969
2034
2034
2034
2034
2034
2034
2329
2329
2329
2329
2329
2329
2329
2329
2329
2329
2345
2345
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2454
2491
2491
(m)
(m)
8.44
8.44
8.44
8.44
8.44
8.44
8.44
8.57
8.57
8.68
8.68
8.68
8.84
8.84
8.84
8.84
8.84
8.84
9.55
9.55
9.55
9.55
9.55
9.55
9.55
9.55
9.55
9.55
9.59
9.59
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.84
9.93
9.93
1.11
1.11
1.11
1.11
1.11
1.11
1.11
1.12
1.12
1.13
1.13
1.13
1.15
1.15
1.15
1.15
1.15
1.15
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.25
1.25
1.25
0.000
0.000
0.000
0.000
0.000
0.021
0.021
0.000
0.001
0.002
0.002
0.002
0.005
0.006
0.006
0.006
0.001
0.000
0.000
0.002
0.000
0.005
0.002
0.004
0.002
0.002
0.001
0.004
0.002
0.003
0.002
0.003
0.003
0.003
0.002
0.004
0.003
0.005
0.002
0.010
0.012
0.011
0.012
0.000
0.000
0.000
0.001
0.003
0.001
0.003
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
32
32
32
32
32
34
35
35
35
35
35
35
35
36
36
36
36
36
36
36
36
36
36
36
36
36
36
36
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
46
46
46
46
46
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Buried
Buried
Buried
Buried
Buried
Buried
Buried
Buried
(m 2 )
(m 3 )
1985
1985
1985
1985
1985
850
2108
2108
2108
2108
2108
2108
2108
2134
2134
2134
2134
2134
2134
2134
2134
2134
2134
2134
2134
2134
2134
2134
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2374
2374
2374
2374
2374
2491
2491
2491
2491
2491
561
2769
2769
2769
2769
2769
2769
2769
2828
2828
2828
2828
2828
2828
2828
2828
2828
2828
2828
2828
2828
2828
2828
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3411
3411
3411
3411
3411
(m)
9.93
9.93
9.93
9.93
9.93
4.25
10.54
10.54
10.54
10.54
10.54
10.54
10.54
10.67
10.67
10.67
10.67
10.67
10.67
10.67
10.67
10.67
10.67
10.67
10.67
10.67
10.67
10.67
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.87
11.87
11.87
11.87
11.87
(m)
1.25
1.25
1.25
1.25
1.25
0.66
1.31
1.31
1.31
1.31
1.31
1.31
1.31
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.33
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.44
1.44
1.44
1.44
1.44
0.000
0.005
0.014
0.004
0.005
0.004
0.007
0.005
0.008
0.010
0.007
0.011
0.001
0.018
0.018
0.003
0.021
0.008
0.002
0.021
0.019
0.015
0.011
0.013
0.008
0.008
0.009
0.007
0.010
0.008
0.010
0.000
0.000
0.000
0.000
0.000
0.003
0.006
0.005
0.006
0.039
0.006
0.000
0.003
0.025
0.004
0.005
0.001
0.017
0.002
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
46
46
46
50
50
50
50
50
50
50
50
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
5
5
5
4
4
4
5
5
5
Buried
Buried
Buried
Buried
Buried
Buried
Buried
Buried
Buried
Buried
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
2374
2374
2374
2510
2510
2510
2510
2510
2510
2510
2510
416
416
416
416
416
416
416
416
416
416
563
563
563
563
563
563
563
563
563
563
563
563
563
563
645
645
645
645
645
645
693
693
693
645
645
645
693
693
693
3411
3411
3411
3762
3762
3762
3762
3762
3762
3762
3762
160
160
160
160
160
160
160
160
160
160
272
272
272
272
272
272
272
272
272
272
272
272
272
272
346
346
346
346
346
346
392
392
392
346
346
346
392
392
392
(m)
11.87
11.87
11.87
12.55
12.55
12.55
12.55
12.55
12.55
12.55
12.55
2.08
2.08
2.08
2.08
2.08
2.08
2.08
2.08
2.08
2.08
2.81
2.81
2.81
2.81
2.81
2.81
2.81
2.81
2.81
2.81
2.81
2.81
2.81
2.81
3.23
3.23
3.23
3.23
3.23
3.23
3.47
3.47
3.47
3.23
3.23
3.23
3.47
3.47
3.47
(m)
1.44
1.44
1.44
1.50
1.50
1.50
1.50
1.50
1.50
1.50
1.50
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.54
0.54
0.54
0.54
0.54
0.54
0.57
0.57
0.57
0.54
0.54
0.54
0.57
0.57
0.57
0.002
0.002
0.001
0.000
0.002
0.007
0.013
0.002
0.001
0.001
0.001
0.025
0.019
0.013
0.019
0.021
0.010
0.029
0.000
0.017
0.027
0.026
0.016
0.017
0.014
0.012
0.008
0.008
0.009
0.011
0.009
0.013
0.007
0.009
0.010
0.008
0.009
0.013
0.009
0.012
0.005
0.009
0.005
0.007
0.032
0.026
0.023
0.031
0.026
0.021
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
5
6
6
6
6
6
7
7
7
8
8
8
8
8
9
9
9
10
10
10
10
10
10
10
10
10
10
10
10
11
11
11
11
11
11
11
11
11
11
11
11
12
12
12
12
13
13
13
13
13
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
693
1119
1119
1119
1119
1119
1153
1153
1153
427
427
427
427
427
1188
1188
1188
532
532
532
532
532
532
532
532
532
532
532
532
531
531
531
531
531
531
531
531
531
531
531
531
371
371
371
371
624
624
624
624
624
392
910
910
910
910
910
958
958
958
168
168
168
168
168
1010
1010
1010
246
246
246
246
246
246
246
246
246
246
246
246
245
245
245
245
245
245
245
245
245
245
245
245
131
131
131
131
326
326
326
326
326
(m)
(m)
3.47
5.60
5.60
5.60
5.60
5.60
5.76
5.76
5.76
2.14
2.14
2.14
2.14
2.14
5.94
5.94
5.94
2.66
2.66
2.66
2.66
2.66
2.66
2.66
2.66
2.66
2.66
2.66
2.66
2.65
2.65
2.65
2.65
2.65
2.65
2.65
2.65
2.65
2.65
2.65
2.65
1.85
1.85
1.85
1.85
3.12
3.12
3.12
3.12
3.12
0.57
0.81
0.81
0.81
0.81
0.81
0.83
0.83
0.83
0.39
0.39
0.39
0.39
0.39
0.85
0.85
0.85
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.35
0.35
0.35
0.35
0.52
0.52
0.52
0.52
0.52
0.014
0.027
0.021
0.020
0.012
0.036
0.036
0.034
0.022
0.034
0.030
0.005
0.027
0.003
0.044
0.026
0.024
0.022
0.016
0.014
0.012
0.010
0.010
0.013
0.000
0.001
0.001
0.034
0.000
0.032
0.028
0.016
0.014
0.008
0.008
0.008
0.009
0.009
0.009
0.011
0.001
0.030
0.025
0.019
0.010
0.009
0.025
0.015
0.018
0.021
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
13
13
13
13
13
13
13
13
13
13
13
13
13
12
12
12
11
11
10
10
10
10
14
14
14
14
14
14
14
14
14
15
15
15
15
15
15
15
15
15
15
15
15
14
14
14
14
14
14
15
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Buried
Open
(m 2 )
(m 3 )
624
624
624
624
624
624
624
624
624
624
624
624
624
371
371
371
531
531
532
532
532
532
982
982
982
982
982
982
982
982
982
598
598
598
598
598
598
598
598
598
598
598
598
982
982
982
982
982
982
1082
326
326
326
326
326
326
326
326
326
326
326
326
326
131
131
131
245
245
246
246
246
246
723
723
723
723
723
723
723
723
723
303
303
303
303
303
303
303
303
303
303
303
303
723
723
723
723
723
723
857
(m)
(m)
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
1.85
1.85
1.85
2.65
2.65
2.66
2.66
2.66
2.66
4.91
4.91
4.91
4.91
4.91
4.91
4.91
4.91
4.91
2.99
2.99
2.99
2.99
2.99
2.99
2.99
2.99
2.99
2.99
2.99
2.99
4.91
4.91
4.91
4.91
4.91
4.91
5.41
0.52
0.52
0.52
0.52
0.52
0.52
0.52
0.52
0.52
0.52
0.52
0.52
0.52
0.35
0.35
0.35
0.46
0.46
0.46
0.46
0.46
0.46
0.74
0.74
0.74
0.74
0.74
0.74
0.74
0.74
0.74
0.51
0.51
0.51
0.51
0.51
0.51
0.51
0.51
0.51
0.51
0.51
0.51
0.74
0.74
0.74
0.74
0.74
0.74
0.79
0.008
0.009
0.009
0.010
0.006
0.013
0.010
0.007
0.009
0.010
0.005
0.015
0.012
0.000
0.011
0.010
0.003
0.004
0.002
0.003
0.004
0.005
0.006
0.007
0.005
0.012
0.014
0.000
0.003
0.013
0.012
0.005
0.004
0.004
0.004
0.004
0.003
0.004
0.005
0.001
0.000
0.004
0.058
0.022
0.021
0.019
0.021
0.023
0.028
0.010
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
15
15
15
15
15
15
15
15
16
16
16
16
17
17
17
17
17
17
17
17
17
18
18
18
18
18
18
18
18
18
18
18
18
18
19
19
20
20
20
20
20
18
19
19
19
19
20
20
20
21
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
1082
1082
1082
1082
1082
1082
1082
1082
1550
1550
1550
1550
1577
1577
1577
1577
1577
1577
1577
1577
1577
511
511
511
511
511
511
511
511
511
511
511
511
511
366
366
653
653
653
653
653
511
366
366
366
366
653
653
653
1668
857
857
857
857
857
857
857
857
1613
1613
1613
1613
1662
1662
1662
1662
1662
1662
1662
1662
1662
230
230
230
230
230
230
230
230
230
230
230
230
230
128
128
353
353
353
353
353
230
128
128
128
128
353
353
353
1834
(m)
(m)
5.41
5.41
5.41
5.41
5.41
5.41
5.41
5.41
7.75
7.75
7.75
7.75
7.88
7.88
7.88
7.88
7.88
7.88
7.88
7.88
7.88
2.56
2.56
2.56
2.56
2.56
2.56
2.56
2.56
2.56
2.56
2.56
2.56
2.56
1.83
1.83
3.26
3.26
3.26
3.26
3.26
2.56
1.83
1.83
1.83
1.83
3.26
3.26
3.26
8.34
0.79
0.79
0.79
0.79
0.79
0.79
0.79
0.79
1.04
1.04
1.04
1.04
1.05
1.05
1.05
1.05
1.05
1.05
1.05
1.05
1.05
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.35
0.35
0.54
0.54
0.54
0.54
0.54
0.45
0.35
0.35
0.35
0.35
0.54
0.54
0.54
1.10
0.011
0.015
0.021
0.012
0.010
0.008
0.017
0.016
0.025
0.012
0.007
0.046
0.032
0.020
0.016
0.012
0.004
0.008
0.005
0.006
0.005
0.011
0.010
0.011
0.015
0.017
0.012
0.012
0.010
0.007
0.008
0.009
0.009
0.011
0.013
0.004
0.008
0.008
0.008
0.005
0.006
0.015
0.012
0.013
0.013
0.010
0.027
0.032
0.025
0.028
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
21
21
21
21
21
21
22
22
22
22
22
22
23
23
23
23
23
23
23
24
24
24
24
25
25
25
25
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
27
27
27
27
27
27
27
27
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
1668
1668
1668
1668
1668
1668
1688
1688
1688
1688
1688
1688
1715
1715
1715
1715
1715
1715
1715
1737
1737
1737
1737
1769
1769
1769
1769
558
558
558
558
558
558
558
558
558
558
558
558
558
558
558
855
855
855
855
855
855
855
855
1834
1834
1834
1834
1834
1834
1873
1873
1873
1873
1873
1873
1926
1926
1926
1926
1926
1926
1926
1969
1969
1969
1969
2034
2034
2034
2034
268
268
268
268
268
268
268
268
268
268
268
268
268
268
268
567
567
567
567
567
567
567
567
(m)
(m)
8.34
8.34
8.34
8.34
8.34
8.34
8.44
8.44
8.44
8.44
8.44
8.44
8.57
8.57
8.57
8.57
8.57
8.57
8.57
8.68
8.68
8.68
8.68
8.84
8.84
8.84
8.84
2.79
2.79
2.79
2.79
2.79
2.79
2.79
2.79
2.79
2.79
2.79
2.79
2.79
2.79
2.79
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
1.10
1.10
1.10
1.10
1.10
1.10
1.11
1.11
1.11
1.11
1.11
1.11
1.12
1.12
1.12
1.12
1.12
1.12
1.12
1.13
1.13
1.13
1.13
1.15
1.15
1.15
1.15
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.48
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.017
0.027
0.022
0.013
0.017
0.024
0.025
0.020
0.012
0.023
0.018
0.000
0.034
0.024
0.022
0.004
0.000
0.007
0.024
0.003
0.000
0.001
0.028
0.024
0.008
0.018
0.018
0.011
0.015
0.009
0.010
0.009
0.006
0.006
0.005
0.005
0.006
0.006
0.001
0.003
0.001
0.006
0.014
0.003
0.003
0.003
0.003
0.003
0.003
0.003
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
28
28
28
28
29
29
29
29
29
29
30
30
30
30
30
30
30
30
30
30
31
31
31
31
31
31
32
32
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
855
855
855
855
855
855
855
855
855
855
855
855
855
855
855
855
855
855
855
855
855
855
1910
1910
1910
1910
1918
1918
1918
1918
1918
1918
1961
1961
1961
1961
1961
1961
1961
1961
1961
1961
1968
1968
1968
1968
1968
1968
1985
1985
567
567
567
567
567
567
567
567
567
567
567
567
567
567
567
567
567
567
567
567
567
567
2329
2329
2329
2329
2345
2345
2345
2345
2345
2345
2439
2439
2439
2439
2439
2439
2439
2439
2439
2439
2454
2454
2454
2454
2454
2454
2491
2491
(m)
(m)
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
4.28
9.55
9.55
9.55
9.55
9.59
9.59
9.59
9.59
9.59
9.59
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.81
9.84
9.84
9.84
9.84
9.84
9.84
9.93
9.93
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.22
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.24
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.25
0.003
0.003
0.004
0.006
0.005
0.005
0.005
0.006
0.006
0.008
0.007
0.007
0.011
0.012
0.013
0.030
0.020
0.011
0.005
0.012
0.015
0.004
0.032
0.017
0.000
0.005
0.036
0.032
0.015
0.023
0.026
0.012
0.028
0.018
0.016
0.009
0.009
0.009
0.017
0.017
0.024
0.027
0.039
0.015
0.023
0.048
0.039
0.032
0.031
0.024
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
32
32
32
32
32
32
32
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
35
35
35
35
35
36
36
36
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
1985
1985
1985
1985
1985
1985
1985
584
584
584
584
584
584
584
584
584
584
584
584
584
584
584
584
584
584
850
850
850
850
850
850
850
850
850
850
850
850
850
850
850
850
850
2108
2108
2108
2108
2108
2134
2134
2134
2491
2491
2491
2491
2491
2491
2491
290
290
290
290
290
290
290
290
290
290
290
290
290
290
290
290
290
290
561
561
561
561
561
561
561
561
561
561
561
561
561
561
561
561
561
2769
2769
2769
2769
2769
2828
2828
2828
(m)
9.93
9.93
9.93
9.93
9.93
9.93
9.93
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
2.92
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
4.25
10.54
10.54
10.54
10.54
10.54
10.67
10.67
10.67
(m)
1.25
1.25
1.25
1.25
1.25
1.25
1.25
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
0.66
1.31
1.31
1.31
1.31
1.31
1.33
1.33
1.33
0.023
0.016
0.024
0.029
0.022
0.009
0.035
0.005
0.021
0.009
0.009
0.009
0.008
0.007
0.007
0.005
0.011
0.011
0.011
0.007
0.011
0.012
0.011
0.009
0.008
0.011
0.011
0.012
0.011
0.009
0.010
0.016
0.021
0.018
0.019
0.020
0.015
0.010
0.000
0.000
0.005
0.013
0.018
0.021
0.044
0.055
0.014
0.044
0.036
0.064
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
36
36
37
37
37
37
37
37
37
37
37
37
37
37
37
37
37
37
37
37
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
38
38
Open
Open
Buried
Buried
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
2134
2134
657
657
657
657
657
657
657
657
657
657
657
657
657
657
657
657
657
657
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
1112
310
310
2828
2828
357
357
357
357
357
357
357
357
357
357
357
357
357
357
357
357
357
357
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
899
96
96
(m)
10.67
10.67
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
3.29
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
5.56
1.55
1.55
(m)
1.33
1.33
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.54
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.81
0.31
0.31
0.058
0.055
0.014
0.010
0.007
0.025
0.016
0.018
0.010
0.014
0.017
0.018
0.015
0.007
0.008
0.004
0.004
0.004
0.004
0.003
0.005
0.005
0.002
0.004
0.003
0.006
0.004
0.004
0.005
0.010
0.011
0.012
0.012
0.007
0.022
0.019
0.021
0.013
0.017
0.016
0.010
0.017
0.013
0.008
0.016
0.009
0.010
0.009
0.033
0.024
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
38
38
38
39
39
39
39
40
40
40
40
40
40
39
41
41
41
41
41
41
41
42
42
42
42
42
42
42
42
42
42
42
42
41
41
41
41
43
43
43
43
43
43
43
43
43
44
44
44
44
Open
Open
Open
Open
Open
Open
Open
Buried
Buried
Buried
Open
Open
Open
Buried
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Buried
Open
Open
Open
Open
Buried
Buried
Buried
Buried
Open
Open
Open
Open
(m 2 )
(m 3 )
310
310
310
359
359
359
359
498
498
498
498
498
498
359
634
634
634
634
634
634
634
525
525
525
525
525
525
525
525
525
525
525
525
634
634
634
634
701
701
701
701
701
701
701
701
701
1112
1112
1112
1112
96
96
96
124
124
124
124
219
219
219
219
219
219
124
336
336
336
336
336
336
336
240
240
240
240
240
240
240
240
240
240
240
240
336
336
336
336
400
400
400
400
400
400
400
400
400
899
899
899
899
(m)
(m)
1.55
1.55
1.55
1.80
1.80
1.80
1.80
2.49
2.49
2.49
2.49
2.49
2.49
1.80
3.17
3.17
3.17
3.17
3.17
3.17
3.17
2.62
2.62
2.62
2.62
2.62
2.62
2.62
2.62
2.62
2.62
2.62
2.62
3.17
3.17
3.17
3.17
3.50
3.50
3.50
3.50
3.50
3.50
3.50
3.50
3.50
5.56
5.56
5.56
5.56
0.31
0.31
0.31
0.34
0.34
0.34
0.34
0.44
0.44
0.44
0.44
0.44
0.44
0.34
0.53
0.53
0.53
0.53
0.53
0.53
0.53
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.46
0.53
0.53
0.53
0.53
0.57
0.57
0.57
0.57
0.57
0.57
0.57
0.57
0.57
0.81
0.81
0.81
0.81
0.008
0.000
0.001
0.009
0.023
0.019
0.009
0.035
0.033
0.018
0.000
0.018
0.011
0.008
0.025
0.026
0.023
0.020
0.003
0.010
0.028
0.025
0.009
0.009
0.010
0.009
0.008
0.002
0.025
0.006
0.004
0.004
0.000
0.017
0.012
0.020
0.013
0.009
0.005
0.004
0.005
0.005
0.026
0.012
0.008
0.008
0.012
0.013
0.016
0.018
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
44
44
44
44
44
44
44
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
46
46
46
46
46
46
46
46
46
46
46
46
47
47
47
47
47
47
47
47
47
47
47
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Open
Open
Open
Open
Buried
Buried
Buried
Buried
Buried
Buried
Open
Open
Buried
Open
Open
Buried
Buried
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
1112
1112
1112
1112
1112
1112
1112
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2357
2374
2374
2374
2374
2374
2374
2374
2374
2374
2374
2374
2374
793
793
793
793
793
793
793
793
793
793
793
899
899
899
899
899
899
899
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3368
3411
3411
3411
3411
3411
3411
3411
3411
3411
3411
3411
3411
497
497
497
497
497
497
497
497
497
497
497
(m)
5.56
5.56
5.56
5.56
5.56
5.56
5.56
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.78
11.87
11.87
11.87
11.87
11.87
11.87
11.87
11.87
11.87
11.87
11.87
11.87
3.97
3.97
3.97
3.97
3.97
3.97
3.97
3.97
3.97
3.97
3.97
(m)
0.81
0.81
0.81
0.81
0.81
0.81
0.81
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.43
1.44
1.44
1.44
1.44
1.44
1.44
1.44
1.44
1.44
1.44
1.44
1.44
0.63
0.63
0.63
0.63
0.63
0.63
0.63
0.63
0.63
0.63
0.63
0.019
0.025
0.027
0.023
0.025
0.025
0.003
0.013
0.015
0.011
0.010
0.009
0.011
0.003
0.053
0.021
0.029
0.031
0.024
0.016
0.070
0.026
0.024
0.032
0.043
0.077
0.126
0.025
0.031
0.028
0.003
0.002
0.025
0.041
0.020
0.036
0.018
0.072
0.034
0.046
0.032
0.021
0.025
0.025
0.015
0.002
0.000
0.000
0.032
0.000
Table S1. WASP hydraulic input parameters for each simulated stream segment under the estimated current
conditions (i.e., the intial model simulation). All stream segment lengths are 200 m. Bottom roughness =
0.04 for open channels; 0.005 for buried channels. This is one of the variables that controls variations in
water velocity (and thereby residence times). Uptake Rate Constant = 0.00543 min -1 for open channels;
0.00121 min-1 for buried channels. *See Fig. S1 for the subbasin location in Gywnns Falls Watershed.
Segment Subbasin* Burial Type Surface Area
Volume
Width
Depth
Slope
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
47
47
47
47
47
49
49
49
49
50
50
47
48
48
48
48
49
49
49
49
50
50
50
50
50
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Buried
Buried
Buried
Buried
Open
Open
Open
Open
Open
Open
Open
Open
Open
(m 2 )
(m 3 )
793
793
793
793
793
858
858
858
858
2510
2510
793
677
677
677
677
858
858
858
858
2510
2510
2510
2510
2510
497
497
497
497
497
571
571
571
571
3762
3762
497
376
376
376
376
571
571
571
571
3762
3762
3762
3762
3762
(m)
3.97
3.97
3.97
3.97
3.97
4.29
4.29
4.29
4.29
12.55
12.55
3.97
3.39
3.39
3.39
3.39
4.29
4.29
4.29
4.29
12.55
12.55
12.55
12.55
12.55
(m)
0.63
0.63
0.63
0.63
0.63
0.67
0.67
0.67
0.67
1.50
1.50
0.63
0.56
0.56
0.56
0.56
0.67
0.67
0.67
0.67
1.50
1.50
1.50
1.50
1.50
0.000
0.000
0.000
0.035
0.008
0.007
0.007
0.017
0.032
0.019
0.038
0.043
0.039
0.041
0.022
0.023
0.013
0.011
0.010
0.003
0.007
0.013
0.012
0.001
0.013
1. WASP modeling methods
2.1 Stream Network
As a first step in the scenario simulations, we delineated the watershed and stream segments as input
data to WASP. We used a 1:24000 NHD stream network as the base data layer. We manually digitized
storm drains greater than or equal to 0.8 m wide (equal to or greater than the approximate median pipe
size in the watershed) and 200 m long (the length of WASP modeling segments), based on the Baltimore
County Storm Drain layer issued from Baltimore County, Maryland, Office of Information Technology.
We merged the storm drain layer with the NHD layer to create a modeling stream network for Gwynns
Falls Watershed (FS03). We subdivided the stream network into 200m long WASP modeling segments to
create a uniform network for the watershed-scale simulations. This length falls near the median of the
stream reaches measured in the study and resulted in 675 stream modeling segments. We identified
buried streams as the digitized storm drain segments in addition to the NHD stream network segments
identified as artificial paths or path connectors. Because WASP can receive a maximum of 50
streamflow inputs as boundary conditions across a river network, simplification of the network in this
large watershed was required. This resulted in the removal of several low order streams throughout the
watershed, which may result in conservative estimates of the influence of low order streams on
downstream NO3- export.
2.2 WASP Model
Our goal was to conduct watershed-scale WASP simulations as an exploratory modeling exercise to
estimate the relative change in watershed NO3- export in response to various stream burial scenarios.
Our approach used a simplified representation of the Gwynns Falls Watershed combined with model
parameter values that were directly measured, estimated, or extracted from the literature. Therefore,
we did not aim to conduct rigorous model calibration; we developed a model based on estimated
current conditions from which we could assess relative changes to nitrate under different levels of
urbanization and stream burial in the watershed.
WASP is a flexible dynamic, differential mass-balance modeling framework used to simulate the
fate and transport of a variety of contaminants in surface water systems. WASP been applied for a
variety of research and regulatory questions [Knightes et al., 2009; Lin et al., 2011] and has recently
been integrated into a modeling system for environmental assessments [Johnston et al., 2011]. Here,
we use WASP7 (referred to as WASP), an enhancement to the original WASP model [R.B. Ambrose Jr,
1987; Robert B. Ambrose Jr, 1988], without additional modifications to the code. The WASP model
simulates water volume and velocity in each segment using the kinematic wave option, and simulates
NO3- concentration in each segment. Detailed equations for the WASP model can be found elsewhere
[R.B. Ambrose Jr, 1987; Robert B. Ambrose Jr, 1988].
We simulated in-stream NO3- uptake as a first order decay rate (k; min-1, see equation 1)
estimated from measured data at both the Cincinnati and Baltimore sites. We applied one uptake rate
to buried streams (0.00121 min-1) and one to open streams (0.00543 min-1). Based upon measured
conditions during the 2011 sampling season, velocity (m d-1) in buried streams was approximately 3.5
times greater than that in open channels. We adjusted stream modeling segment velocities in the WASP
model to approximate this trend by modifying the Manning’s roughness coefficient. Based upon these
simulations, we applied a final roughness coefficient for buried (Manning’s = 0.005) and open
(Manning’s = 0.04) streams.
Because the WASP model structure allows a maximum of 50 stream flows as boundary
conditions for river systems, we divided the watershed into 50 sub-basins (FS02), each receiving daily
streamflow and NO3- concentration inputs. We input uniform average daily summer base flows (m3 s-1)
estimated for the 21 June through 22 September 2011 period, the year that summer uptake rates were
measured, based on the records from the closest downstream USGS stream gage to each sub-basin
(FS03). We calculated average percent baseflow from the streamflow records using the 2006 version of
Baseflow Program [Arnold and Allen, 1999; Arnold et al., 1995] and scaled the results using an area to
discharge ratio for each sub-basin. We estimated a single average summer NO3- concentration from
three of the four USGS station records. We averaged NO3- concentrations for the summer periods of
2000-2009 (N = 127 to 156, depending on the stream gage), which covered a range of hydrological
conditions at each gage, but exhibited limited variation in average NO3- concentrations. Because of the
shorter period of record at the fourth gage, Dead Run at Franklintown, Maryland (USGS 01589330), we
used average summer NO3- concentration data in the Dead Run Watershed from Pennino et al. [Pennino
et al., 2014]. We applied these NO3- concentrations as boundary conditions for each of the 50 subbasins
based upon values estimated at the stream gage within the closest downstream proximity.
WASP requires estimates of multiple hydraulic variables for each modeled stream segment. We
estimated widths and depths for each stream segment in the sub-basins using standard regional
regression equations from techniques used in the Grid Based Mercury Model (see below) [Dai et al.,
2005]. We modified the width regression equation based upon measurements in the watershed during
summer 2008 (S. Kaushal, unpublished data, 2013). We estimated slopes for each modeling segment by
extracting elevation data at each segment’s upstream and downstream point using Spatial Analyst in
ArcGIS 9.3.1 (ESRI, Redlands, California) and calculating the difference in distance (a constant 200 m)
and elevation between the points. The full set of WASP stream segment hydraulic input parameters are
listed in Table S1.
Our simulation approach required several assumptions and simplifications. First, WASP
simulates varying depths for each stream segment using the continuity equation for the mass of water
and based on roughness coefficients and stream widths. However, to best generalize measurements of
uptake across the watershed, we did not simulate variations in uptake rates with depth. Other
potentially important features of the system that were not modeled include hydrologic exchanges
between the channel, floodplain, and subsurface waters [Helton et al., 2011].
2.3 Stream Burial Scenarios
We used the following stream burial scenarios to assess changes in NO3- export at the watershed outlet:
(1) Increasing the proportion of the stream network that was buried by 5% increments. Burial was
evenly distributed across the 200 m stream segments; (2) Concentrated burial that reflects potential
suburban development (all 85 segments in suburban subbasins (FS03); 1700 m buried, or 12.2% of the
total stream network length), and (3) Concentrated burial that reflects urban development along the
lower watershed mainstem (85 segments in urban subbasins (FS03) for a total of 1700 m of buried
stream channel, same length used for the suburban scenario).
We also conducted two simulations to determine whether modeled changes in NO3- export
were a result of changes in N-removal rates due to burial, changes in hydrology resulting from burial, or
a combination of the two. We held uptake rates constant and modified stream velocity via variations in
the Manning’s roughness coefficient for the 50 subbasins in the first scenario and held hydrologic inputs
constant and varied N-uptake rates in the second scenario. We based stream velocity and uptake rates
upon whether the stream was buried or open.
2.4 WASP stream segment geomorphology calculations
Width (m) = 1.7# * Drainage area (km2) 0.3916##
(3)
# = original coefficient was 2.933 (from Dai et al. [Dai et al., 2005]); final coefficient (1.7) was adjusted
based on measurements from summer 2008 (S Kaushal, unpublished data)
## = estimated using techniques from Dai et al. [Dai et al., 2005]
Depth (m) = 0.33# * Drainage area (km2) 0.2964##
(4)
## = estimated using techniques from Dai et al. [Dai et al., 2005]
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