diff --git a/swmmanywhere/swmm_text_tools.py b/swmmanywhere/swmm_text_tools.py
new file mode 100644
index 00000000..1a3e1d37
--- /dev/null
+++ b/swmmanywhere/swmm_text_tools.py
@@ -0,0 +1,83 @@
+# -*- coding: utf-8 -*-
+"""Created 2024-01-22.
+
+@author: Barnaby Dobson
+"""
+import re
+
+import numpy as np
+
+
+def overwrite_section(data: np.ndarray,
+                      fid: str, 
+                      section: str):
+    """Overwrite a section of a SWMM .inp file with new data.
+
+    Args:
+        data (np.ndarray): Data array to be written to the SWMM .inp file.
+        fid (str): File path to the SWMM .inp file.
+        section (str): Section of the SWMM .inp file to be overwritten.
+    """
+    # Read the existing SWMM .inp file
+    with open(fid, 'r') as infile:
+        lines = infile.readlines()
+    
+    # Create a flag to indicate whether we are within the target section
+    within_target_section = False
+    
+    # Iterate through the lines and make modifications as needed
+    with open(fid, 'w') as outfile:
+        for ix, line in enumerate(lines):
+        
+            if line.strip() == section:
+                within_target_section = True
+                outfile.write(line)  # Write the start section header
+                
+                # Write headers
+                i = 1
+                while lines[ix + i][0] == ';':
+                    outfile.write(lines[ix + i]) # Write column headers
+                    i+=1
+                    
+                example_line = lines[ix + i]
+                print('example_line {1}: {0}'
+                      .format(example_line.replace('\n',''), section))
+                print('note - this line must have at least as many column')
+                print('entries as all other rows in this section\n')
+                pattern = r'(\s+)'
+    
+                # Find all matches of the pattern in the input line
+                matches = re.findall(pattern, example_line)
+                
+                # Calculate the space counts by taking the length of each match 
+                space_counts = [len(x) + len(y) for x,y in
+                                 zip(matches, example_line.split())]
+                if len(space_counts) == 0:
+                    if data.shape[0] == 0:
+                        pass
+                    else:
+                        print('no template for data?')
+                else:
+                    space_counts[-1] -= 1
+                    new_text = ''
+                    if data is not None:
+                        for i, row in enumerate(data):
+                            if section != '[CONTROLS]':
+                                formatted_row = [
+                                    '{0:<{1}}'.format(x, 
+                                                      max(y, len(str(x)) + 1)) 
+                                    for x, y in zip(row, space_counts)
+                                ]
+                                new_line = '{0}\n'\
+                                    .format(''.join(formatted_row))
+                                new_text += new_line
+                            else:
+                                new_text = row
+        
+                    outfile.write(new_text)  # Write the new content
+                    outfile.write('\n')
+            elif re.search(r'\[.*?\]', line):
+                within_target_section = False
+                outfile.write(line)  # Write the end section header
+            elif not within_target_section:
+                outfile.write(line)  # Write lines outside the target section
\ No newline at end of file
diff --git a/tests/test_swmm_text_tools.py b/tests/test_swmm_text_tools.py
new file mode 100644
index 00000000..a62d7541
--- /dev/null
+++ b/tests/test_swmm_text_tools.py
@@ -0,0 +1,28 @@
+import os
+import shutil
+
+from swmmanywhere import swmm_text_tools as stt
+
+
+def test_overwrite_section():
+    """Test the overwrite_section function."""
+    # Copy the example file to a temporary file
+    fid = os.path.join(os.path.dirname(os.path.abspath(__file__)),
+                       '..',
+                        'swmmanywhere',
+                        'defs',
+                        'basic_drainage_all_bits.inp')
+    temp_fid = 'temp.inp'
+    shutil.copy(fid, temp_fid)
+    try:
+        data = [["1","1","1","1.166","100","500","0.5","0","empty"],
+                ["2","1","1","1.1","100","500","0.5","0","empty"],
+                ["subca_3","1","1","2","100","400","0.5","0","empty"]]
+        
+        section = '[SUBCATCHMENTS]'
+        stt.overwrite_section(data, temp_fid, section)
+        with open(temp_fid, 'r') as file:
+            content = file.read()
+        assert 'subca_3' in content
+    finally:
+        os.remove(temp_fid)
\ No newline at end of file