# Impact of the Revetment on the Seashore in the Region of Babie Doly (KM 93.6-93.9), Poland
## 3 Results
### Shore Protection along KM 93.6-93.9  
Pursuant to the Act of 25 September 2015 amending the Act on establishing the long-term Coastal Protection Programme (\"Program ochrony brzegow morskich\"; Dz.U. of 23 October 2015, item 1700), the shore stretch from Oksywie to Mechelinki (KM 89.1-96.6) is protected by beach nourishment and hard coastal protection structures. The functioning of revetments along this section--including the rubble revetment within the shore stretch of KM 93.6-93.9--is therefore in compliance with the recommendations of the aforementioned Act. However, none of the documents of the shoreline development records held by IBW PAN (Institute of Hydro-Engineering of Polish Academy of Sciences, Gdansk, Poland) contains information on the described revetment. Furthermore, according to the materials available at IBW PAN, the theoretical shoreline defined according to the Coastal Protection Programme, runs in the landward part of the top of a local small coastal cliff (Figure 12). This would mean that the rubble revetment in question is not included in the register of the shore protection structures kept by the Maritime Office in Gdynia. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & \multicolumn{2}{c}{**Chainage**} & \multirow{2}{*}{**Crest Elevation**} & \multirow{2}{*}{**Construction Time**} \\  & **Beginning [KM]** & **End [KM]** & & & & **Structure** \\  & & & & & & **[m a.s.l. ]** & **Time** \\ \hline \multirow{4}{*}{5.} & \multirow{4}{*}{89.89} & \multirow{4}{*}{90.19} & \multirow{4}{*}{0.30} & \multicolumn{4}{c}{Stone embankment on the slope covered with a reinforced concrete slab with a slope of ca. 1: 3.5; the whole structure supported on the seaward side by a tight wooden palisade} \\  & & & & & & \\ \cline{1-1}  
For a very long time, until 2018, the coastal cliff in this area and its hinterland belonged to a large closed military area (which included, i.a., the navy airfield). It is very likely that the structure was erected by the army on a tight budget, without any prior analysis of local conditions or a technical design, and without the consent of relevant civil authorities of the public administration, including the Maritime Office. This type of situation mainly took place in the 1980s, when, due to a lack of sufficient financial resources, such solutions were used to temporarily protect the shore against erosion. In subsequent years, these structures were removed or modernised by the Maritime Office in Gdynia. The authors of this study are not aware of any such structures (apart from the analysed stretch of shore) to be currently found on the coast under the jurisdiction of the Maritime Office in Gdynia. Figure 11: Torpedo station put into service in 1942. The blue arrow indicates the approximate location of KM 93.6–93.9. Regardless of the genesis of the structure in question and its low aesthetic value, the intuitive premises that led to its construction were legitimate. Furthermore, its sloping riprap construction--in contrast to vertical revetments--facilitates the sea wave energy dissipation and reflects waves to a small extent only, which does not result in the formation of a standing wave or intense scouring of sand in the foreground of the structure. As already mentioned above, the analysed area is characterised by longshore sediment transport with a long-term direction from south to north. This results in extensive erosion processes along KM 93.6-93.9, and, therefore, the need for anti-erosion protection of the shore is indisputable. In this context, the revetment is highly effective in preventing coastal erosion. The removal of the revetment, e.g., for aesthetic reasons, will result in coastal abrasion at this location, posing a threat to the safety of buildings situated in the immediate vicinity.