*4.1.2 Prediction of erosion indicators and soil losses using physically-based erosion models*

Until recently, some highly sophisticated erosion models were adapted and tested in predicting EG and classical gully erosion processes around the Mubi region. Several works by [24, 32] evaluated the efficiencies of some foreign physically-based erosion models such as EGEM, RUSLE-2, and WEPP models, and were compared with some earlier tested empirical and mathematical equations in the same Mubi region.

In addition, [11] computed soil erosion on a watershed using a Kriging interpolation technique in ArcGIS software 10.3 model. On the other hand, the works of [9, 20, 26, 30, 44], reported some suitable conservation measures for erosion controls around the Mubi area, but without quantitative information.

**Table 6** presents the reports of earlier predicted soil losses using the Revised Universal Soil Loss Equation (RUSLE-2) in ArcGIS software [11, 12], as well as the empirical, EGEM and WEPP models in the Mubi region [24, 32, 45]. Results from the different prediction tools used in the Mubi area reported an average soil loss of 3.52 tons/ha/year from a watershed area covering 148.43 km2 using the RUSLE-2 software at Mubi-South LGA. Earlier works by [24] that tested an EGEM software technology recorded an average soil loss of between 0.37 and 1.37 tons/ha/year. at Mubi-South, and still found a relatively lower range of 0.50 - 1.15 tons/ha/year. of soil loss at Mubi-North LGA. The wide difference between the RUSLE-2 and EGEM predictions within the neighboring erosion sites accounted for the RUSLE-2


#### **Table 4.**

*Some reported hydrological and physicochemical properties of soils of the Mubi Region.*

as having over predictions compared to the EGEM outputs. This was perhaps due to the larger area coverage by the RUSLE-2 during the research, compared to the EGEM applied to EG erosion channels with smaller sizes. However, future trials and revalidation of RUSLE-2, and other technologies are strongly recommended towards developing suitable conservation alternatives in the Mubi region. Further trials by [32, 45] involving EGEM, WEPP, and empirical models show that the


*Evaluation of Soil Erosion and Its Prediction Protocols around the Hilly Areas of Mubi Region… DOI: http://dx.doi.org/10.5772/intechopen.100477*

#### **Table 5.**

*Annual soil loss observed at some gully erosion sites in the Mubi area.*

observed erosion strongly correlated with the empirical (r2 = 0.67) than with both EGEM (r2 = 0.57) and the WEPP (r2 = 0.53) models. The results suggest opportunities for adaptability of even the more sophisticated foreign models around the Mubi region, and therefore, the need for further trials of other efficient erosion models towards the selection of more realistic and/or suitable tool for erosion management around the Mubi region.

#### **4.2 Economic implications of soil erosion in the Mubi region**

Although volumes of research works on economic implications of soil erosion exist elsewhere, the Mubi region is still facing a dearth of information on such an agenda in monetary terms, apart from the few research results reported by [46]. There are still no other published records of economic analysis on soil erosion devastations in the Mubi region.

**Table 7** presents the results of some analyzed economic implications of soil and soil nutrient losses observed at 4 farm locations in the Mubi area in 2003 and 2004. The estimated weights of soils and their inherent nitrogen (N), phosphorus (P), and potassium (K) losses were quantified at costs within the range of \$305 and \$5698 for the study sites in both years. The gross cost of the nutrient loss over the 2 years was as high as \$19,377, considering the small-sized erosion channels. Although, these values seem to fall within considerable limits, nutrient losses in larger erosion channels might be very disturbing and prohibitive.


*Keywords: RUSLE = revised universal soil loss equation, EGEM = ephemeral gully erosion, WEPP = water erosion prediction project, LGA = local government area. Adapted from [11, 32].*

#### **Table 6.**

*Predicted soil loss estimates from ephemeral gully (EG) features using some adapted physically-based erosion models in the Mubi region.*

The results in **Table 8** presents a similar economic analysis of the quantity of soil loss by gully erosion as reported by [46] in the same Mubi region. However, such economic analysis on erosion-related researches has not yet been reported, apart from those reported by [46]. The results show that locations such as the Muvur site with wider and/or deeper gullies recorded larger soil removals with proportionate


*Evaluation of Soil Erosion and Its Prediction Protocols around the Hilly Areas of Mubi Region… DOI: http://dx.doi.org/10.5772/intechopen.100477*

> **Table 7.**

*Soil and nutrient loss and their cost estimates per hectare per annum (2003–2004).*


*Keywords: (1) equivalent weight of tipper load (156 T) = 6160 kg, (2) unit cost of a tipper load = \$40. Adapted from [46].*

#### **Table 8.**

*Soil loss and cost estimates.*

economic losses, while other locations with the narrowest and/or shallowest channels such as the Gella site, had lesser soil and associated economic losses. The gross cost of soil loss (\$19,377) was over twice the cost of nutrient loss (\$34,840) during the 2 study seasons. These soil and nutrient loss cost estimates (\$54,217) appear very high and prohibitive, if converted into the Nigerian local currency (N20,060,290). This is an amount that could pay off 1 month salary bills of about 50 professors in the Nigerian Universities.

### **4.3 Erosion management practices adopted around the Mubi region**

The erosion features in the Mubi region have also received considerable management efforts from farmers, residents, government officials, and environmental scientists over the years. **Table 9** presents some of the management measures adopted at some villages across the Mubi region [10, 32]. The report details the major soil degradation sources adopted conservation practices, and their corresponding impacts on arable agriculture around the Mubi region. The major soil degradation sources include soil erosion such as sheet, rill, and gully, Sloughing along gullies, impeded drainages, and soil exhaustion. The majority of the gullies and stream bank erosion features have been controlled over time with such as stone lines/bunds, sandbag lines, vegetative barriers, earthencontour bunds, and hillside-terraces. In addition, soil exhaustion caused by continuous cropping and selective plant nutrient uptakes, have been remedied with the application of organic manure, and some other soil-enriching mulching practices to restore soil quality after erosion damages. These measures have shown some proven protection of soil surfaces against the menacing effects of such as gullying, siltation problems, and channelized erosion spread in the Mubi region.

A handful of researchers such as [10, 11, 17, 18, 20, 26–28, 30, 31] suggested several, but varying soil erosion control options for implementation around the Mubi region. According to [30, 31], overgrazing, deforestation, and indiscriminate bush burning that leaves the soils bare during dry seasons up to the onsets of rainfalls makes the soils more vulnerable to surface destructions at the slightest impacts of rain splash, rills, or gullying activities in the region.


**Table 9.** *Field and conservation practices for controlling erosion processes around the Mubi region.*

#### *Evaluation of Soil Erosion and Its Prediction Protocols around the Hilly Areas of Mubi Region… DOI: http://dx.doi.org/10.5772/intechopen.100477*
