The South-Western Spur Hill Unit serves as a terminal transitional zone where the Lushai hill system descends into the alluvial plains of the Barak Valley. Characterized by elongated narrow ridges and dissected flanks, this unit features an elevation profile of 30 – 45 m on its northern side, increasing to 40 – 60 m in the southern portion adjacent to the Narsingpur area before rising further into the higher altitudes of the Lushai hills. Functioning as a primary runoff generation zone, its northern slopes feed the Jalenga (Halenga) river and Pakoi Beel, while the southern runoff contributes to the Dhalai river, which joins the Rukni river system approximately 4–5 km beyond the southern boundary of the RoI.

Geomorphic Characteristics: The terminal spur ridges marking the transition from upland terrain to floodplain. Typical ridge lengths of 1–2 km and widths between 200–600 m. Ridges generally trend south to north. 

Hydrological Dynamics: Serves as a critical runoff generation zone for the surrounding lowlands. The northern runoff flows into the Jalenga river (Halenga), traversing the western flood basin and feeding the Pakoi Beel and northern Barak floodplains. The southern drainage runoff feeds the Dhalai river, which flows SSW to NNE to join the Rukni river 4–5 km beyond the Narsingpur area. Seasonal channels from the slopes eventually integrate into the larger floodplain drainage network.

The Settlement Ridges are a slightly raised alluvial terrace positioned immediately east of the Western Flood Basin. Morphologically, this unit represents a natural levee remnant or older alluvial terrace formed during historical river migration. It serves as the primary zone for village settlements, homestead plantations, and local road networks due to its superior drainage and relative height. The ridges follow a unique tripartite branching structure. It is composed of three distinct "flanks" that converge in the south, forming a Y-shaped linear tract with elevation ranging between 27 to 33 m, generally trending higher toward the mid-southern region, around the tripartite junction.

The Western Flank extends approximately 2.5 km in a South-to-North direction. It is the most prominent arm with an average width of 150–200 m. The Eastern Flank extends approximately 1.7 km in a SW-to-NE direction, running parallel to the western embankment of the Rukni River. It has an average width of 100 m. The Southern Stem acts as the base/stem from which the other two flanks branch. It extends 1 km toward the SSW from the junction point, with an average width of 100 m.

Settlement Density: Human concentration is significantly higher towards the south, clustering around the higher ground of the junction.

The Central Agricultural Plain is a broad, flat alluvial unit located east of the western settlement ridge and west of the Rukni River levee system. It is characterized by fine-grained sediments, clay-rich soils, and a landscape primarily dedicated to paddy and other type of cultivation. The plain is divided into two major sections, with the primary agricultural heartland situated between the western and eastern settlement ridges spanning approximately 2.1 km in a North-to-South direction, maintaining a consistent width of 450–600 m through the north and center, before tapering significantly to approximately 170 m in the southern portion. The narrowing southern tail is marked by oxbow remnants, indicating the historical meandering path of the Rukni River. It maintains a decreasing elevation profile towards the North and West maintaining 27 – 29 m. elevation on the eastern side and 25 – 27 m. in the western side.

The Riverbank Patches are linear strips located on the western banks of the Rukni River, situated specifically between the river channel and the constructed embankment.

Hydrology & Land Use: Dominantly used for paddy cultivation in the central area and mustard, vegetables and paddy on the levee system. Since the Serlui Dam was installed (c. 2004) in Mizoram, flooding of the Rukni has become a very rare occurrence. Temporary waterlogging in the main section is typically caused by inefficient discharge through settlement culverts toward the western lowlands, rather than river overtopping. 

This is the easternmost physiographical unit of the Narsingpur region and serves as its central drainage axis. The corridor including the embankments and the levee system on both sides measure around 700 m. at its widest and 300 m at its narrowest part. The corridor is wider downstream with the meanders while tapered towards upstream where it maintains a straighter path. The Rukni river (known as the Serlui in Mizoram) flows diagonally SSW → NNE on a bearing of ≈ 029°. It follows a meandering path approximately 8.5 km in length.The levees serve several purposes like protection of adjacent agricultural lands from flooding. Confinement of the active river channel and regulation of seasonal runoff flow. To note: Since the etablishment of the Rukni/Serlui dam in the upstream in Mizoram in 2004, no flooding is experienced in the Rukni. It maintains a regulated water level perennialy.

Elevation Profile: The riverbed elevation within this area is 31 m at the south-western extent and descends to 27 m at its mouth in the north-eastern extent. The difference of 4 meters over a length of 8.5 kms of meandering path resulting in very slow water discharge.

Oxbow Remnants: There are three distinct oxbows located on the left (west) bank, now physically separated from the main channel by the western embankment. The Largest Oxbow is situated at the tripartite junction of the settlement ridges. Two smaller remnants located on the eastern settlement ridge, following the line of the western embankment.

The Western Flood Basin acts as the primary low-lying catchment for the Narsingpur region, functioning as a natural backswamp and seasonal storage zone for excess runoff. Spanning approximately 5 km in length (North-South) and between 1 to 1.25 km in width (East-West), this depression maintains a elevation profile of 21 – 26 m above mean sea level. A defining feature of this unit is the National Highway dyke, which extends diagonally from Northeast to Southwest, effectively bifurcating the floodplain. This anthropogenic modification has transformed the eastern segment into perennial arable land, although it retains patches of depressions that remain waterlogged during the monsoon months.

Geomorphic Origin: A backswamp or floodplain depression formed through prolonged sediment deposition behind river levee ridges.

Hydrology & Anthropogenic Impact: The National Highway dyke cuts diagonally across the basin, dividing it into distinct segments. Characterized as perennial arable land due to the dyke's influence, though monsoon-driven waterlogging persists in lower depressions. Functions as a seasonal floodwater storage area and a critical natural groundwater recharge zone. Contains intermittent wetlands (beels) that remain inundated or as swampy marshland for most of the year.

The National Highway dyke is an artificially raised embankment that diagonally crosses the Western Flood Basin in a SSW–NNE orientation, roughly parallel to the Rukni River. This dyke acts as a major transportation corridor. As it bifurcates a floodplain that maintains an uneven yet gradually decreasing elevation profile from east to west, the dyke serves as a critical hydraulic barrier. Consequently, the dyke has helped render much of the eastern portion into a perennial arable land with specific low-lying patches and depressions remaining waterlogged throughout the rainy season.

This bifurcation has resulted in perennial waterlogging along the eastern edge of the embankment. Unlike seasonal flooding, these stagnant patches experience almost no water flow except during the height of the monsoon. This persistent stagnation renders these specific areas unsuitable for farming or bio-culture and creates a significant risk of groundwater pollution due to the prolonged infiltration of untreated surface water.

Functional Role: Serves as a major regional corridor. Influences the distribution and retention of floodwaters across the basin, effectively modifying the natural backswamp dynamics.

Hydraulic & Topographic Interaction: Splits the Western Flood Basin into two distinct hydrological zones. The basin maintains a gradual, uneven decrease in elevation from East to West. The dyke acts as a linear barrier to the natural westward drainage flow. Results in perennial water accumulation along the eastern levee edges. Creates a mosaic of perennial arable land and monsoon-period waterlogged depressions in the eastern segment of the Western Flood Basin.

The study area lies at an average elevation of 32.8 m above mean sea level (MSL), with elevation ranging between 21.1 m and 44.5 m. The terrain is predominantly characterized by floodplains composed of younger alluvium, with alluvial plains extending towards the western fringes. The general slope of the terrain is very gentle, typical of riverine alluvial plains.

Geologically, the area belongs to the Quaternary system, consisting of Holocene and Pleistocene alluvial formations. The lithology is composed primarily of unconsolidated deposits including pale to dirty grey silt, sand, clay, silty clay, sandy clay, yellowish brown coarse river sand, gravel and concretions. The soil texture varies across the region. Fine loamy to fine silty soils dominate the northern parts, while coarse loamy dystrochrept soils and cut-off meander deposits occur towards the southern and western areas.

Groundwater occurs under shallow unconfined conditions. The water table elevation averages around 30 m MSL, resulting in a depth to water level of approximately 1–2 m in most areas during the pre-monsoon period. In the western fringes, groundwater levels are particularly shallow, ranging between 0–1 m, while depths of 2–3 m are observed in southern areas. During the post-monsoon period, groundwater levels generally range between 1–2 m below ground level.

Morphology

Average Elevation:	32.8 m above mean sea level (MSL).
Elevation Range:	21.1 m to 44.5 m.
Terrain Type:	Riverine alluvial plains with a very gentle slope.
Geological System:	Quaternary system (Holocene and Pleistocene formations).
Lithology:	Unconsolidated silt, sand, clay, gravel, and concretions.

Soil Characteristics

Northern Region:	Fine loamy to fine silty soils.
Southern & Western Regions:	Coarse loamy dystrochrept soils and cut-off meander deposits.

Groundwater Hydrology

Aquifer Condition:	Shallow and unconfined.
Average Water Table:	Approximately 30 m MSL.
Pre-Monsoon Depth:	Generally 1-2m; notably shallow (0-1 m) in western fringes and deeper (2-3 m) in southern areas.
Post-Monsoon Depth:	Ranges between 1-2 m below ground level.

Ground Water Quality

Parameter	Pre-Monsoon Range	Post-Monsoon Range
pH (Acidity)	6.06 - 8.33	6.0 - 8.5
EC (Conductivity)	21.54 - 667.8 μS/cm	22.1 - 544.9 μS/cm
TDS (Solids)	14.22 - 440.75 mg/L	14.59 - 359.63 mg/L
SAR (Sodium Absorption Ratio)	0.2 - 1.5	0.2 - 2.2
Sodium Concentration	20 - 60	20 - 40
Magnesium Ratio	< 50%	< 50%

Localized Hazards

Iron Concentration	> 1 ppm on the north eastern fringes.
Arsenic	> 10 ppb on the north-eastern and south-western side

Source : Report on Aquifer Mapping and Management Plan of Cachar District, Assam (2021-22) : Central Ground Water Board

The study area falls within the Barak River basin, where drainage is primarily controlled by a hierarchical network of tributaries. The Sonai River functions as a major tributary of the Barak, while the Rukni stream acts as a secondary tributary within this system, conveying runoff from the upland terrains of Mizoram into the plains of Cachar district.

Rukni River System

The Rukni stream originates in the hill ranges of Mizoram at approximately 24.0278° N, 92.7414° E, at an elevation of about 228 m above mean sea level. It flows for nearly 112.42 km before joining the Sonai River near 24.6614° N, 92.8871° E at an elevation of around 46 m. Hydrologically, the river is linked to the Serlui Dam outlet, which regulates upstream discharge. Further downstream, it is joined by the Dhalai River from the western side, augmenting its flow before it continues toward the Barak basin.

Within the RoI, the Rukni follows a south-west to north-east course (bearing ~33.09°), traversing a meandering channel stretch of approximately 6.7 km. This segment represents a critical drainage conduit linking the hilly catchments of Mizoram with the alluvial plains.

Secondary Drainage Features

The Jalenga stream (locally known as Halenga) flows northward along the western boundary of the RoI, effectively demarcating its edge. During the monsoon season, it contributes flow to the Pakoi Beel, receiving runoff from the Paloi catchment to the south and south-west, while also directing excess flow toward the north-west in the direction of Silkuri.

Surface Water Resources

The study area contains both natural and man-made perennial water bodies. Natural features include five water bodies (covering approximately 0.058 sq km), largely representing remnant oxbow formations of the Rukni River. In addition, over 270 small to medium-sized man-made ponds contribute around 0.11 sq km of perennial water surface area. These water bodies play a vital role in irrigation, fisheries, and domestic water use.

Floodplain Features and Wetlands

The floodplain exhibits clear geomorphological evidence of historical channel migration. Three oxbow lakes are located primarily in the southern and south-eastern parts of the RoI, formed through meander cutoffs of the Rukni River.

A significant intermittent wetland (locally referred to as a beel or haor) is present along the north-western boundary. This low-lying depression experiences prolonged seasonal inundation, limiting agricultural activity. Only during extended dry periods is limited paddy cultivation practiced.

Collectively, these features indicate a dynamic floodplain system characterized by lateral channel migration, wetland formation, and pronounced seasonal hydrological variability.

The Narsingpur region experiences a humid subtropical climate, characterized by mild winters, warm pre-monsoon conditions, and humid summers influenced by the southwest monsoon. The climate is primarily governed by monsoonal rainfall patterns, which play a critical role in shaping the district’s hydrology, agriculture, and water resource availability.

Annual and Seasonal Rainfall Distribution

The area receives very high annual rainfall, ranging between approximately 3725 mm and 3938 mm during the period 2023–2025. Rainfall distribution is highly seasonal:

Southwest Monsoon (June–September): ~60–65% of annual rainfall
Pre-monsoon (March–May): ~25–30%
Post-monsoon (October–November): ~5–8%
Winter (December–February): Minimal contribution

The monsoon season clearly dominates the hydrological cycle, with peak rainfall occurring in June and July, where monthly values often exceed 700 mm.

Monthly Distribution Pattern

Rainfall begins to increase from March, driven by convective thunderstorms, and rises sharply through April and May. A pronounced peak is observed during June and July, followed by a gradual decline from August onwards. Post-monsoon rainfall extends into October, indicating a delayed withdrawal of monsoon, while winter months remain largely dry.

Monthly Rainfall Table (mm)
Data Period : 2023–2025

Year	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total
2023	12	25	180	320	520	650	720	610	420	210	90	35	3792
2024	15	30	210	350	480	700	680	580	380	190	80	30	3725
2025	10	28	195	330	550	720	750	600	410	220	85	40	3938

Inter-Annual Variability and Trends

Comparison across the three years indicates consistently high rainfall totals with moderate variability. There is a slight increasing trend in peak rainfall intensity, particularly in 2025. Greater concentration of rainfall within fewer high-intensity events. This suggests a shift toward more intense and short-duration precipitation, a pattern increasingly associated with climate variability.

Hydrological Significance

The high rainfall regime contributes significantly to groundwater recharge through infiltration. Sustenance of perennial ponds, wetlands, and rivers. Maintenance of soil moisture levels, supporting rain-fed agriculture. However, the concentration of rainfall in short periods increases surface runoff, soil erosion, flooding and waterlogging risks

Temperature Analysis
Seasonal Temperature Pattern

The temperature regime in the Narsingpur region remains moderate and stable, with clear seasonal variation:

Winter (Dec–Feb): 18–20°C
Pre-monsoon (Mar–May): 26–28°C
Monsoon (Jun–Sep): 28–29°C
Post-monsoon (Oct–Nov): Gradual decline to ~25–27°C

The monsoon period exhibits temperature stabilization, primarily due to cloud cover and continuous rainfall.

Average Monthly Temperature (°C)

Consistent across years with minor variation

Year	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
2023	18.5	20.0	24.5	26.5	27.5	28.0	28.2	28.0	27.8	26.5	23.5	20.0
2024	18.8	20.2	25.0	27.0	27.8	28.2	28.5	28.3	28.0	26.8	23.8	20.2
2025	18.6	20.1	24.8	26.8	27.6	28.1	28.3	28.2	27.9	26.6	23.6	20.1

Inter-Annual Stability
Across the period 2023–2025 temperature variation remains within a narrow range (±0.3°C). There is no significant short-term warming or cooling trend and a marginal increase in average temperature is noticeable but not conclusive. This indicates a thermally stable climate system in the short term.

Climatic Influence

Temperature patterns in the district are strongly influenced by rainfall and cloud cover, high humidity levels and seasonal monsoon dynamics. The absence of extreme temperature fluctuations supports continuous vegetation growth and agricultural activity.

Key Observations:

Strong dependence on monsoon rainfall. Increasing intensity of rainfall events. Stable temperature regime with minimal fluctuation makes this area a highly potent region for groundwater recharge and water resource availability.

Implications for Water Resources and Agriculture

Positive impacts are abundant rainfall supported rain-fed agriculture, enhanced groundwater recharge potential and sustainabilty of surface water bodies and ecosystems.

Emerging concerns could be increased risk of flooding and waterlogging. Soil erosion due to high-intensity rainfall and uneven rainfall distribution affecting crop cycles.

Conclusion

The climate of the Narsingpur region during 2023–2025 reflects a stable temperature regime combined with a highly seasonal and increasingly intense rainfall pattern. While the overall climatic conditions remain favorable for agriculture and water availability, the emerging trend of high-intensity rainfall events highlights the need for improved water management strategies, conservation of ponds and wetlands and climate-resilient agricultural planning.

The land use pattern of the Narsingpur region reflects a typical floodplain agrarian landscape, where agricultural production, wetlands, and dispersed settlements coexist within a dynamic fluvial environment influenced by the Rukni–Sonai–Barak river system.

Agriculture

Agricultural land constitutes the largest share of the land use pattern, covering approximately 3.33 sq km (56.3% of the total RoI). Cultivation is predominantly single-cropped, with paddy as the principal crop, reflecting the agro-ecological suitability of the floodplain. Farming is largely rainfed, with crop cycles closely aligned to the monsoon and dependent on seasonal rainfall and shallow groundwater availability. Historically, parts of the area—particularly the northern section—were supported by a localized irrigation system comprising pipelines and three pump stations, two drawing water from the Rukni River and one from an oxbow lake. However, this infrastructure is no longer functional and has been largely dismantled, increasing dependence on rainfall.

In the absence of reliable irrigation, farmers in the northern areas manage seasonal water shortages by pumping water from homestead ponds, while the use of borewells remains limited. There are also reported, though unverified, instances of water being purchased for irrigation during critical periods, indicating emerging stress on water access. Additionally, there is a growing trend of conversion of agricultural land for fisheries, as well as small-scale commercial and residential construction, reflecting shifting livelihood patterns and rising land-use pressure. While fisheries may offer alternative income opportunities and align with the floodplain ecology, such unregulated conversions—along with expanding built-up areas—can fragment cultivable land, reduce overall agricultural productivity, and alter local hydrological regimes. This trend underscores the need for careful land-use planning to balance economic diversification with the preservation of agricultural sustainability.

Horticulture

Horticultural land occupies approximately 0.1247 sq km (2.1%), and is primarily concentrated along the natural levees on both sides of the Rukni River. Cultivation in these slightly elevated, well-drained areas is dominated by seasonal vegetables, with mustard being a commonly grown crop. Agricultural practices are largely low-input in nature, with minimal use of chemical fertilizers and pesticides, and irrigation is mainly supported by rainfall and occasional river water abstraction. Production is largely subsistence-oriented, catering to household consumption with limited surplus entering local markets.

Perennial Waterbodies

Permanent water bodies, including ponds and oxbow lakes, cover approximately 0.1647 sq km (2.8%), playing a crucial role in local water storage. These water bodies support household-level fisheries, provide supplementary irrigation—particularly during dry periods—and act as important components of the local hydrological system within the floodplain environment.

Lowland & Wetlands

Wetland areas cover approximately 0.4899 sq km (8.3%), comprising low-lying depressions, seasonal beels, and oxbow remnants shaped by the floodplain dynamics of the Rukni and Jalenga (Halenga) rivers within the Barak basin. A significant portion of these wetlands, particularly in the western flood basin, consists of perennial and intermittently waterlogged zones dominated by invasive vegetation such as Ipomoea carnea and water hyacinth, with no active cultivation practices observed. Fishing activity is largely opportunistic and seasonal, occurring mainly during periods of flooding or peak monsoon, while organized pisciculture is absent.

The western side of the flood basin, especially beyond the highway dyke towards the north, is characterized by extensive perennial marshland interspersed with slightly raised patches, none of which are utilized for agriculture. Hydrologically, these wetlands function as natural water retention zones; however, water quality is a concern, likely due to shallow water depths, limited circulation, and very low discharge or flow conditions, which may contribute to stagnation and ecological degradation over time.

Settlements

Rural settlements account for approximately 1.374 sq km (23.2%) of the total area, reflecting dispersed habitation patterns typical of rural floodplain environments. These settlements are generally located on relatively elevated ground to avoid seasonal waterlogging.

Shallow Water Table Risk

The shallow water table (1–2 m below ground level) poses multiple environmental and infrastructural risks. During the monsoon, the water table can rise to the surface, creating anaerobic soil conditions that adversely affect crop growth, particularly in low-lying beels where only intermittent paddy cultivation is feasible. This condition also weakens soil bearing capacity, leading to structural instability in buildings and road infrastructure, where water infiltration into subgrades can accelerate pothole formation and surface failure. Additionally, underground infrastructure such as pipelines is vulnerable to continuous seepage, corrosion, and flooding, reducing their functional lifespan.

From a public health perspective, the shallow and unconfined aquifer offers minimal natural filtration, allowing surface contaminants—including agricultural runoff and domestic waste—to quickly infiltrate groundwater sources. Conventional sanitation systems like pit latrines and soak pits become ineffective under such conditions, increasing the risk of groundwater contamination and waterborne diseases, especially during peak monsoon when the water table reaches the surface. Furthermore, frequent wet-dry cycles alter soil chemistry through redox reactions, potentially mobilizing elements like iron and arsenic into groundwater. Coupled with high evaporation rates, these processes may also contribute to localized soil salinization.

Loss of Agricultural Land due to Infrastructure Development

Recent road expansion activities have led to the conversion of approximately 0.1553 sq km of agricultural land, accounting for about 2.6% of the total RoI and nearly 4.7% of existing farmland. This reflects increasing development pressure within a predominantly agrarian landscape. While improved connectivity enhances accessibility and supports regional mobility, the reduction in cultivable land may have localized impacts on agricultural productivity and livelihood sustainability. Given the dominance of agriculture in the area, continued and unregulated land conversion could lead to fragmentation of farmland, reduced food production capacity, and shifts away from traditional agrarian practices. This underscores the need for careful monitoring and balanced land-use planning to ensure long-term environmental sustainability and community resilience.