diff --git a/autotest/test_parameters.py b/autotest/test_parameters.py
new file mode 100644
index 00000000..c8cb87e1
--- /dev/null
+++ b/autotest/test_parameters.py
@@ -0,0 +1,33 @@
+from pprint import pprint
+
+from numpy.testing import assert_equal
+
+from pywatershed.parameters import Parameters, PrmsParameters
+from pywatershed.base.parameters import _set_dict_read_write
+
+from utils import assert_dicts_equal
+
+
+def test_param_dd_param(domain):
+    # round trip from read-only to read-write to read-only
+    # use a PRMS Parameter file for now
+    domain_dir = domain["param_file"].parent
+    params = Parameters.from_netcdf(
+        domain_dir / "parameters_PRMSGroundwater.nc"
+    )
+    # These both copy by default
+    param_dd = params.to_dd()
+    params2 = Parameters(**param_dd.data)
+
+    assert_dicts_equal(params.data, params2.data)
+
+    param_dd.data_vars["gwflow_coef"] *= 4
+    params3 = Parameters(**param_dd.data)
+
+    try:
+        assert_dicts_equal(params.data, params3.data)
+        assert False
+    except AssertionError:
+        pass
+
+    return
diff --git a/autotest/utils.py b/autotest/utils.py
index 496d56d3..d6cd0037 100644
--- a/autotest/utils.py
+++ b/autotest/utils.py
@@ -1,3 +1,4 @@
+from types import MappingProxyType
 import numpy as np
 
 print_ans = False
@@ -41,3 +42,22 @@ def assert_or_print(
     # Always fail if printing answers
     assert not print_ans
     return
+
+
+def assert_dicts_equal(dic1, dic2):
+    assert set(dic1.keys()) == set(dic2.keys())
+
+    # add cases as needed
+    for kk, vv in dic1.items():
+        if isinstance(vv, (dict, MappingProxyType)):
+            assert_dicts_equal(dic1[kk], dic2[kk])
+        elif isinstance(vv, np.ndarray):
+            np.testing.assert_equal(dic1[kk], dic2[kk])
+        else:
+            if (
+                isinstance(vv, float)
+                and np.isnan(dic1[kk])
+                and np.isnan(dic2[kk])
+            ):
+                continue
+            assert dic1[kk] == dic2[kk]
diff --git a/environment.yml b/environment.yml
index 4de85c24..71d39656 100644
--- a/environment.yml
+++ b/environment.yml
@@ -49,5 +49,5 @@ dependencies:
       - flake8
       - git+https://github.com/modflowpy/flopy.git
       - jupyter_black
-      - modflow-devtools
+      - modflow-devtools < 1.0.0
       - pylint
diff --git a/pywatershed/base/parameters.py b/pywatershed/base/parameters.py
index 551ce99c..ed9ec9cf 100644
--- a/pywatershed/base/parameters.py
+++ b/pywatershed/base/parameters.py
@@ -1,3 +1,4 @@
+from copy import deepcopy
 from types import MappingProxyType
 from typing import Union
 
@@ -51,7 +52,16 @@ def __init__(
         metadata: dict = None,
         encoding: dict = None,
         validate: bool = True,
+        copy: bool = True,
     ) -> None:
+        if copy:
+            dims = deepcopy(dims)
+            coords = deepcopy(coords)
+            data_vars = deepcopy(data_vars)
+            metadata = deepcopy(metadata)
+            encoding = deepcopy(encoding)
+            validate = deepcopy(validate)
+
         super().__init__(
             dims=dims,
             coords=coords,
@@ -95,17 +105,16 @@ def get_dim_values(
             return {kk: self.dims[kk] for kk in keys}
 
     def to_xr_ds(self) -> xr.Dataset:
-        # must pass as dictionary not a mapping proxy: dict = mp | {}
         return dd_to_xr_ds(_set_dict_read_write(self.data))
 
     def to_nc4_ds(self, filename) -> None:
-        # must pass as dictionary not a mapping proxy: dict = mp | {}
         dd_to_nc4_ds(_set_dict_read_write(self.data), filename)
         return
 
-    def to_dd(self) -> DatasetDict:
-        # must pass as dictionary not a mapping proxy: dict = mp | {}
-        return DatasetDict(_set_dict_read_write(self.data))
+    def to_dd(self, copy=True) -> DatasetDict:
+        return DatasetDict.from_dict(
+            _set_dict_read_write(self.data), copy=copy
+        )
 
     @classmethod
     def merge(cls, *param_list, copy=True, del_global_src=True):
@@ -121,10 +130,12 @@ def merge(cls, *param_list, copy=True, del_global_src=True):
 def _set_dict_read_write(mp: MappingProxyType):
     dd = mp | {}
     for kk, vv in dd.items():
-        if isinstance(vv, MappingProxyType):
-            dd[kk] = _set_dict_read_write(dd[kk] | {})
+        if isinstance(vv, (dict, MappingProxyType)):
+            dd[kk] = _set_dict_read_write(vv)
         elif isinstance(vv, np.ndarray):
-            vv.flags.writeable = True
+            # copy is sufficient to make writeable
+            # https://numpy.org/doc/stable/reference/generated/numpy.copy.html
+            dd[kk] = dd[kk].copy()
 
     return dd
 
diff --git a/pywatershed/static/metadata/parameters.yaml b/pywatershed/static/metadata/parameters.yaml
index 93a8286f..82efe03f 100644
--- a/pywatershed/static/metadata/parameters.yaml
+++ b/pywatershed/static/metadata/parameters.yaml
@@ -2079,7 +2079,7 @@ ppt_zero_thresh:
   help: The minimum/zero threhold for precipitation
   maximum: 0.0
   minimum: 0.0
-  modules:
+  modules: None
   type: F
   units: inches
 precip_units:
@@ -3057,7 +3057,7 @@ stream_tave_init:
   help: Cold-start stream average stream temperature
   maximum: unbounded
   minimum: unbounded
-  modules:
+  modules: None
   type: F
   units: unknown
 subbasin_down: