diff --git a/marquette/conf/config.yaml b/marquette/conf/config.yaml
index 5694c15..4fb2600 100644
--- a/marquette/conf/config.yaml
+++ b/marquette/conf/config.yaml
@@ -1,6 +1,6 @@
 name: MERIT
 data_path: /projects/mhpi/data/${name}
-zone: 73
+zone: 74
 create_edges:
   buffer: 0.3334
   dx: 2000
@@ -19,7 +19,7 @@ create_N:
 create_TMs:
   MERIT:
     save_sparse: True
-    TM: ${data_path}/zarr/TMs/MERIT_FLOWLINES_${zone}
+    TM: ${data_path}/zarr/TMs/sparse_MERIT_FLOWLINES_${zone}
     shp_files: ${data_path}/raw/basins/cat_pfaf_${zone}_MERIT_Hydro_v07_Basins_v01_bugfix1.shp
 create_streamflow:
   version: merit_conus_v3.0
diff --git a/marquette/merit/_TM_calculations.py b/marquette/merit/_TM_calculations.py
index 8c845cc..537868a 100644
--- a/marquette/merit/_TM_calculations.py
+++ b/marquette/merit/_TM_calculations.py
@@ -1,6 +1,7 @@
 import logging
 from pathlib import Path
 
+import binsparse
 import geopandas as gpd
 import matplotlib.pyplot as plt
 import numpy as np
@@ -8,6 +9,7 @@
 import xarray as xr
 import zarr
 from omegaconf import DictConfig
+from scipy import sparse
 from tqdm import tqdm
 
 log = logging.getLogger(__name__)
@@ -56,6 +58,85 @@ def create_HUC_MERIT_TM(
     xr_dataset.to_zarr(zarr_path, mode="w")
 
 
+def format_pairs(gage_output: dict):
+    pairs = []
+    for comid, edge_id in zip(gage_output["comid_idx"], gage_output["edge_id_idx"]):
+        for edge in edge_id:
+            # Check if upstream is a list (multiple connections)
+            if isinstance(edge, list):
+                for _id in edge:
+                    # Replace None with np.NaN for consistency
+                    if _id is None:
+                        _id = np.NaN
+                    pairs.append((comid, _id))
+            else:
+                # Handle single connection (not a list)
+                if edge is None:
+                    edge = np.NaN
+                pairs.append((comid, edge))
+
+    return pairs
+
+
+def create_coo_data(sparse_matrix, root: zarr.Group):
+    """
+    Creates coordinate format (COO) data from river graph output for a specific gage.
+
+    This function processes the river graph data (specifically the 'ds' and 'up' arrays)
+    to create a list of pairs representing connections in the graph. These pairs are then
+    stored in a Zarr dataset within a group specific to a gage, identified by 'padded_gage_id'.
+
+    Parameters:
+    gage_output: The output from a river graph traversal, containing 'ds' and 'up' keys.
+    padded_gage_id (str): The identifier for the gage, used to create a specific group in Zarr.
+    root (zarr.Group): The root Zarr group where the dataset will be stored.
+
+    """
+    values = sparse_matrix["values"]
+    pairs = format_pairs(sparse_matrix)
+
+    # Create a Zarr dataset for this specific gage
+    root.create_dataset("pairs", data=np.array(pairs), chunks=(10000,), dtype="int32")
+    root.array("values", data=np.array(values), chunks=(10000,), dtype="float32")
+
+
+def create_sparse_MERIT_FLOW_TM(
+    cfg: DictConfig, edges: zarr.hierarchy.Group
+) -> zarr.hierarchy.Group:
+    """
+    Creating a sparse TM that maps MERIT basins to their reaches. Flow predictions are distributed
+    based on reach length/ total merit reach length
+    :param cfg:
+    :param edges:
+    :param huc_to_merit_TM:
+    :return:
+    """
+    log.info("Using Edge COMIDs for TM")
+    COMIDs = np.unique(edges.merit_basin[:])  # already sorted
+    gage_coo_root = zarr.open_group(Path(cfg.create_TMs.MERIT.TM), mode="a")
+    merit_basin = edges.merit_basin[:]
+    river_graph_len = edges.len[:]
+    river_graph = {"values": [], "comid_idx": [], "edge_id_idx": []}
+    for comid_idx, basin_id in enumerate(
+        tqdm(
+            COMIDs,
+            desc="Creating a sparse TM Mapping MERIT basins to their edges",
+            ncols=140,
+            ascii=True,
+        )
+    ):
+        col_indices = np.where(merit_basin == basin_id)[0]
+        total_length = np.sum(river_graph_len[col_indices])
+        if total_length == 0:
+            print("Basin not found:", basin_id)
+            continue
+        proportions = river_graph_len[col_indices] / total_length
+        river_graph["comid_idx"].append(comid_idx)
+        river_graph["edge_id_idx"].append(col_indices.tolist())
+        river_graph["values"].extend(proportions.tolist())
+    create_coo_data(river_graph, gage_coo_root)
+
+
 def create_MERIT_FLOW_TM(
     cfg: DictConfig, edges: zarr.hierarchy.Group
 ) -> zarr.hierarchy.Group:
@@ -113,19 +194,27 @@ def create_MERIT_FLOW_TM(
         for idx, proportion in zip(indices, proportions):
             column_index = np.where(river_graph_ids == river_graph_ids[idx])[0][0]
             data_np[i][column_index] = proportion
-    data_array = xr.DataArray(
-        data=data_np,
-        dims=["COMID", "EDGEID"],  # Explicitly naming the dimensions
-        coords={"COMID": COMIDs, "EDGEID": river_graph_ids},  # Adding coordinates
-    )
-    xr_dataset = xr.Dataset(
-        data_vars={"TM": data_array},
-        attrs={"description": "MERIT -> Edge Transition Matrix"},
-    )
-    log.info("Writing MERIT TM to zarr store")
-    zarr_path = Path(cfg.create_TMs.MERIT.TM)
-    xr_dataset.to_zarr(zarr_path, mode="w")
-    # zarr_hierarchy = zarr.open_group(Path(cfg.create_TMs.MERIT.TM), mode="r")
+    
+    if cfg.create_TMs.MERIT.save_sparse:
+        log.info("Writing to sparse matrix")
+        gage_coo_root = zarr.open_group(Path(cfg.create_TMs.MERIT.TM), mode="a")
+        matrix = sparse.csr_matrix(data_np)
+        binsparse.write(gage_coo_root, "TM", matrix)
+        log.info("Sparse matrix written")
+    else:
+        data_array = xr.DataArray(
+            data=data_np,
+            dims=["COMID", "EDGEID"],  # Explicitly naming the dimensions
+            coords={"COMID": COMIDs, "EDGEID": river_graph_ids},  # Adding coordinates
+        )
+        xr_dataset = xr.Dataset(
+            data_vars={"TM": data_array},
+            attrs={"description": "MERIT -> Edge Transition Matrix"},
+        )
+        log.info("Writing MERIT TM to zarr store")
+        zarr_path = Path(cfg.create_TMs.MERIT.TM)
+        xr_dataset.to_zarr(zarr_path, mode="w")
+        # zarr_hierarchy = zarr.open_group(Path(cfg.create_TMs.MERIT.TM), mode="r")
 
 
 def join_geospatial_data(cfg: DictConfig) -> gpd.GeoDataFrame:
diff --git a/marquette/merit/create.py b/marquette/merit/create.py
index 8fe5095..c6da455 100644
--- a/marquette/merit/create.py
+++ b/marquette/merit/create.py
@@ -31,6 +31,7 @@
 from marquette.merit._TM_calculations import (
     create_HUC_MERIT_TM,
     create_MERIT_FLOW_TM,
+    # create_sparse_MERIT_FLOW_TM,
     join_geospatial_data,
 )
 
@@ -237,4 +238,7 @@ def create_TMs(cfg: DictConfig, edges: zarr.Group) -> None:
         log.info("MERIT -> FLOWLINE data already exists in zarr format")
     else:
         log.info("Creating MERIT -> FLOWLINE TM")
+        # if cfg.create_TMs.MERIT.save_sparse:
+        #     create_sparse_MERIT_FLOW_TM(cfg, edges)
+        # else:
         create_MERIT_FLOW_TM(cfg, edges)
diff --git a/requirements.txt b/requirements.txt
index 5db2daa..fdb9120 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,4 @@
+git+https://github.com/ivirshup/binsparse-python.git@main
 dask[complete]
 polars
 dask-expr