The Role of Sustainable Land and Water Conservation Practices in Flood Mitigation ^†

Abstract

Promising Land and Water Conservation Practices (LWCPs) play a vital role in restraining floods and keeping the land productive. Floods are usually destructive and increase the risk of drowning, waterborne diseases, malnutrition, and multiple long-term knock-on effects. Similarly, the 2022 monsoon season has prompted the most severe flood in Pakistan. The main objective of this review is to highlight the importance of LWCPs as an adaptation strategy for flood mitigation. Moreover, different LWCPs are discussed concerning studies carried out in different regions and published in scientific journals, technical reports, and notes from experts. It was observed that both the in situ and ex situ LWCPs have a significant effect on reducing land degradation and flood control. Additionally, most of the reviewed studies showed a positive impact of LWCPs on agricultural productivity, primarily due to the retention of nutrients and moisture. Hence, land conservation practices including biological and agronomic measures (i.e., contour farming, conservation tillage, strip cropping, vegetation, etc.), and mechanical or engineering methods (i.e., check dams, bunding, ponds/reservoirs, etc.) are aimed at reducing the run-off velocity and mitigating the floods. The results of this study will encourage the stakeholders to adopt LWCPs to lessen flood hazards and uplift agricultural production by limiting the land degradation processes.

1. Introduction

Flooding is the most common natural disaster and can cause widespread devastation, resulting in loss of life and damage to infrastructure, and it can compromise medium-to-long-term health impacts. According to WHO (2022) [1] more than two billion people worldwide were affected by floods from 1998 to 2017, worldwide. Similarly, a devastating flood hit Pakistan during the 2022 monsoon rains and inundated thousands of hectares of agricultural land, drowned livestock, damaged infrastructure, and wiped out urban areas. The damage was particularly severe in southern Punjab and the Sindh and Balochistan provinces (Figure 1). Heavy and prolonged rainfalls, snow melts, and unmanaged watersheds are the main drivers of destructive floods. Two main factors regulate the flood, i.e., runoff depth and peak discharge [2]. Watershed management through promising LWCPs reduce runoff and sediment; this reduction is generally achieved by altering the runoff processes. The high-intensity runoff erodes the topsoil and contributes to the sedimentation of downstream reservoirs, consequently decreasing the live water storage of the reservoirs [3].

Figure 1. Detailed flood inundation map of southern Punjab, Sindh, and Balochistan (The image contains modified Copernicus Sentinel data (2022), processed by ESA, CC BY-SA 3.0 IGO—Source: [4]).

Soil erosion has been a critical issue and has induced numerous inflated environmental issues. Yousuf and Singh, (2019) [5] stated that different degradation mechanisms have degraded almost 52% of the total productive land. Moreover, due to the acute shortage of water [6,7,8], and under the emerging climate change scenarios [9], we must emphasize the expansion and adoption of effective measures for land and water conservation to mitigate floods.

Thus, mitigation against floods could be achieved by reducing the runoff intensity and by increasing the runoff lag time through standard LWCPs and flood protection measures. These practices include contour farming, conservation tillage, strip cropping, crop rotation, cover crops, water diversion channels, spillways (gully control), field outlets, terracing, spurs, check dams, and rainwater harvesting structures.

2. Land and Water Conservation Practices

LWCPs help to conserve water, reduce erosion, keep the land fertile, reduce runoff intensity, and mitigate devastating floods. Following are the two broader categories of LWCPs that can sustain the environment and enhance agricultural production.

2.1. Agronomical or Biological Practices

These practices are usually in-situ and reduce the impact of raindrops by protecting the soil surface, and improving the infiltration rate, resulting in less runoff generation and soil loss due to erosion. Vegetation or cover crops are one of the agronomic practices to tackle soil erosion and reduce the runoff intensity. All of the agricultural operations starting from plowing, making ridges and furrows, planting, inter-cultural, etc. are performed along contours, called contour farming. These operations hinder the runoff and reduce its velocity, which in turn reduces soil loss. Moreover, the runoff intensity also depends on the selection of crops, the substantial biomass, the widespread rooting system, and the dense canopy cover; these parameters reduce the erosive impact of rainfall and hinder the runoff [10]. The close-growing and dense cover crops are the best for controlling the erosion process, i.e., groundnut, cowpea, grams, etc. Similarly, other agronomical or biological practices are listed in Table 1.

Table 1. Some findings from the literature regarding land and water conservation practices.

LWCPs		Main Findings	Reference
Agronomical/Biological measures
	Grassed waterway	Decreases runoff coefficient and reduces nutrients loss	[11]
	Conservation tillage	Reduces runoff, improves infiltration rate, and reduces evaporation loss	[5]
	Strip cropping	Reduces the runoff velocity, increases the time of concentration, conserves soil moisture, and increases crop production	[5]
	Land configuration methods (i.e., bed- and ridge-furrow)	Reduces runoff and soil and nutrient loss, conserves soil moisture, and higher gain in productivity and profitability	[5,10]
	Agroforestry measures	Reduces soil erosion by up to 10%, reduces runoff, and increases water infiltration	[10]
Mechanical/Engineering methods
	Terracing	Reduces runoff velocity, improves infiltration, and controls soil erosion	[5,12]
	Field outlet	Safe disposal of rainwater from one field to another	---
	Water diversion channel	Divert runoff water and control runoff losses	[10]
	Spillway	Disposes of runoff water safely and reclaims severely eroded gullies	-
	Bunding (i.e., contour bunding, graded bunding, and peripheral bunds)	Conserves soil moisture, disposes of excess runoff water safely, and reduces erosion	[10]
	Contour trenching	Reduces runoff velocity and conserves soil moisture	[5,10]

2.2. Mechanical or Engineering Methods

Mechanical measures or engineering methods of soil and water conservation are mainly designed to alter the land slope, lessen the runoff velocity and sedimentation, and safely transport the runoff water from the upstream to the downstream side. Small rainwater harvesting ponds and dams are suitable for plugging gullies and controlling erosion and thus reducing runoff velocity. Similarly, check dams are also built across gullies to confront the velocity of intense runoff. Moreover, preventing a flood from turning into a calamity is a fundamental goal of a check dam system. Wang et al. (2021) [13] also reported that check dams significantly increase runoff infiltration and effectively mitigate flood processes. The importance of other mechanical/engineering methods is listed in Table 1.

3. Discussion

The LWCPs play a significant role in controlling erosive runoff by reducing the flow velocity; moreover, these practices enhance the time of concentration, thus increasing the infiltration and crop production. Moreover, strip copping had an effective role in regulating surface runoff and floods. Check dams are one of the prominent measures of mechanical/engineering methods, reducing the flood peak and flood volume and thus mitigating the floods [5].

Globally, check dams are used to control soil and water erosion, reduce runoff velocity, and improve infiltration. Wang et al. (2021) [13] reported that runoff lag times significantly increased by constructing check dams. Similarly, the construction of small dams also obstructs the runoff and discourages the flood processes [5]. Hence, LWCPs significantly reduce soil erosion, trap silt, reduce runoff velocity by hindering flowing water, and evade the risk of floods by changing local geomorphology, thus maintaining environmental sustainability.

4. Conclusions

LWCPs are imperative in controlling land degradation, reducing runoff velocity, and thus mitigating the risk of devastating floods. Moreover, these practices increase infiltration and in situ moisture conservation, improve soil and water quality, and in turn effectively enhance overall farm production. Therefore, the holistic adoption of these practices at watershed levels is crucial for flood mitigation, ecosystem protection, and sustaining agricultural productivity. Moreover, new policies regarding regional land and water conservation must be framed, keeping in view the damages perceived from the recent floods, and the post-assessment of these policies must be followed to increase efficiency.