Western Rwanda contains rugged terrain, aligned valleys, drainage anomalies, escarpments, and other linear geomorphic features that may reflect underlying geological structures. The region is associated with the Lake Kivu sector of the western branch of the East African Rift and with older basement and metasedimentary terrains belonging to the Kibaran and Karagwe-Ankole belts. Structural mapping in this setting, however, remains constrained by limited access to detailed, consistently mapped, and openly accessible geological and fault data.

1.2 Problem Statement

Structural mapping in Rwanda — and Western Province specifically, despite its position within the tectonically active western branch of the Albertine Rift — remains constrained by limited access to detailed, publicly available geological and fault maps. Conventional structural interpretation relies heavily on lithological control, which is often unavailable, outdated, or proprietary in data-scarce settings. This creates a gap for reconnaissance-level structural assessment in contexts where open elevation data exist but licensed geological data do not — a gap directly relevant to exploration screening, geohazard assessment, and infrastructure siting in the region.

The central problem addressed by this study is therefore not simply the absence of a fault map, but the absence of a reproducible procedure for distinguishing persistent, geologically plausible morpholineaments from non-tectonic or processing-related linear features derived from open elevation data.

1.3 Research Gap

Many DEM-based lineament studies present extraction results without adequately quantifying the sensitivity of results to DEM source and resolution, hillshade illumination direction, edge-detection parameters, the contribution of drainage and topographic grain, the possibility of anthropogenic and vegetation-related artefacts, and the uncertainty associated with interpreting a topographic lineament as a geological structure. This study improves on a simple extraction exercise by assessing the reproducibility and relative confidence of the mapped features.

1.4 Aim

To develop and evaluate a reproducible open-data workflow for mapping and ranking DEM-derived morpholineaments in Western Province, Rwanda, using geomorphometric, hydrological, seismic, geological, and land-cover evidence.

1.5 Scientific Question

Can digital elevation-derived lineaments be assigned meaningful structural confidence — in the absence of a lithological or licensed fault map — through cross-validation against independent, freely available datasets (seismicity, global active fault compilations, drainage network anomalies) and existing field geophysical data?

A secondary, more specific question: do the dominant lineament orientations extracted from the DEM in Western Province align with the structural trends reported in the literature for the Kibaran Belt fabric and the Albertine Rift's western branch?

1.6 Objectives

● 1. Derive a full geomorphometric parameter stack (slope, curvature, TRI, TPI, hydrology) for Western Province from open DEM data.

● 2. Extract DEM-based lineaments and characterize their orientation distribution (rose diagram, length-weighted).

● 3. Independently validate extracted lineaments using open seismicity records, the GEM Global Active Faults Database, and drainage-pattern anomalies (elbow bends, offsets).

● 4. Compare observed lineament orientations against published regional tectonic trends.

● 5. Synthesize results at district/sector level within Western Province to produce a reconnaissance-level structural indicator map, explicitly stating its limitations relative to field-verified geological mapping.

1.7 Working Hypotheses

Null hypothesis

The orientation, density, and spatial distribution of DEM-derived morpholineaments do not differ significantly from patterns expected from terrain geometry, drainage, anthropogenic features, and random spatial processes.

Alternative hypothesis

A subset of DEM-derived morpholineaments is persistent across independent data and processing methods and shows statistically or geomorphologically meaningful association with regional structural trends, drainage anomalies, seismicity, or mapped active faults.

1.8 Scope and Constraints

The study is limited to Western Province, Rwanda, comprising seven districts: Karongi, Ngororero, Nyabihu, Nyamasheke, Rubavu, Rusizi, and Rutsiro. Western Province was selected because it includes the Lake Kivu sector of the western branch of the East African Rift, rugged mountainous terrain, strong relief contrasts, and dense drainage — conditions well suited to investigating the relationship between topography, drainage, and possible structural control.

The project uses only openly available or already-held datasets and does not require licensed fault or lithology shapefiles. The study is limited to reconnaissance-level interpretation and does not attempt to produce a definitive geological fault map or replace field-based geological mapping. Field geophysical data (HVSR) already collected along the Vunga corridor are noted as a source of potential future cross-validation but are not incorporated into this version of the study.